Military Depots: The Navy Needs Improved Planning to Address Persistent Aircraft Maintenance Delays While Air Force Maintenance Has Generally Been Timely

Three Air Force and three Navy aviation depots maintain critical fixed-wing aviation platforms, such as the KC-135 aerial refuelers and F/A-18 fighters. The ability of these depots to complete maintenance on time directly affects military readiness because delays reduce the time aircraft are available for operations and training.

Senate Report 115-262, accompanying a bill for the Fiscal Year 2019 National Defense Authorization Act, contained provisions that GAO examine the Department of Defense's (DOD) aviation depots. GAO's report evaluates the extent to which 1) the Air Force and Navy aviation depots completed selected fixed-wing aircraft maintenance on time from fiscal year 2014 through 2019, and 2) the Air Force and Navy accurately planned for depot maintenance requirements from fiscal year 2014 through 2019 and addressed any associated challenges.

GAO selected a non-generalizable sample of 18 Air Force and 18 Navy fixed-wing aircraft types; analyzed maintenance and planning data for fiscal year 2014 through 2019; and interviewed service officials.

The Air Force and Navy varied in the extent that they completed depot maintenance on time for selected fixed-wing aircraft in fiscal years 2014 through 2019. Specifically, GAO's analysis of aggregate maintenance data found that:

Air Force depots completed aircraft maintenance on time or early in 5 of 6 years, with percentages for on-time or early-completion maintenance ranging from 78 to 90 percent.

Navy depots completed aircraft maintenance late for each of the 6 years, with percentages for on-time or early-completion maintenance ranging from 45 to 63 percent. Navy fixed-wing aircraft have spent over 62,000 more days in maintenance than expected since fiscal year 2014.

The Air Force generally has accurately planned for depot maintenance requirements for selected fixed-wing aircraft during fiscal year 2014 through 2019, but the Navy has not. Both services have initiatives underway to improve planning for aviation depot maintenance; however, GAO identified planning challenges that the Navy has not fully addressed:

The Navy has not effectively used historical data to analyze turnaround time—total days planned for depot maintenance periods—and established accurate planning targets for aircraft maintenance packages.

Navy depot planners do not have visibility into aircraft maintenance that is performed outside the depots by an operational unit or other maintenance facility—information critical to planning for the condition and depot maintenance needs of individual aircraft.

The Navy does not yet have formal processes and related guidance for communication and coordination between depot stakeholders to inform maintenance requirements planning.

Without addressing these challenges, the Navy cannot appropriately plan for depot maintenance workload and will likely continue to experience maintenance delays that reduce the time aircraft are available for operations and training.

GAO is making three recommendations to the Navy: to use historical data to set turnaround time targets for depot maintenance; provide planners information on maintenance performed outside the depots; and establish processes for communication between depot stakeholders. DOD concurred with all three recommendations.

Three Air Force and three Navy aviation depots maintain the readiness of  critical fixed-wing aircraft, such as KC-135 aerial refuelers and F/A-18A-D  fighters that are required for military operations. The ability of these  depots to complete maintenance on time directly affects military  readiness as maintenance delays reduce the amount of time during which  aircraft are available for operations and training. A key component of  completing maintenance on time is accurately forecasting workload  requirements so the aviation depots can appropriately plan for and  execute their maintenance workload. The Air Force and Navy have  invested about $3.3 billion in their aviation depots’ capital budgets from  fiscal years 2014 through 2019, and officials stated they have  implemented a variety of initiatives intended to improve on-time  performance.

Since 2009, we have issued several reports on the challenges  experienced at the Department of Defense’s (DOD) maintenance depots,  including deteriorating equipment and facility condition, difficulty in filling  critical personnel skills, and growing maintenance backlogs. Our prior  work has found that these and other factors have contributed to depot  maintenance delays. We reported in 2018 that, in part due to these  challenges at the depots, the Air Force and Navy have struggled to meet  fixed-wing aircraft availability goals, hampering unit readiness. We have  made 39 recommendations to improve DOD depot operations. DOD has  concurred with 38 of our 39 recommendations and has fully implemented  three.

Senate Report 115-262 accompanying a bill for the National Defense  Authorization Act for Fiscal Year 2019 included provisions for us to  examine DOD’s aviation depots and maintenance operations. Our report  examines the extent to which 1) the Air Force and Navy aviation depots  completed selected fixed-wing aircraft maintenance on time from fiscal  year 2014 through 2019, and 2) the Air Force and Navy accurately  planned for depot maintenance requirements for selected fixed-wing  aircraft from fiscal year 2014 through 2019 and addressed any associated  challenges. We have separate ongoing reviews to examine maintenance  timeliness and related issues at the Army and Marine Corps key weapons  systems depots and Navy shipyards.

For objective one, we selected a non-generalizable sample of 18 Air  Force and 18 Navy types of fixed-wing aircraft, including fighters,  bombers, and aerial refuelers, based on information from Air Force and  Navy maintenance data, and a review of our prior work. These aircraft  had maintenance completed in fiscal years 2014 through 2019 at the Air  Force’s three Air Logistics Complexes and the Navy’s three Fleet  Readiness Centers. We selected this time period so we could identify and  obtain insight on historical data trends regarding maintenance timeliness  for the selected aircraft. For each aircraft, we collected data on the date  maintenance began and was completed for individual aircraft, as well as  the original estimate of time (in days) needed to complete maintenance.  We also collected updated estimates if available. We used this  information to calculate the difference between the number of days  planned for maintenance (using the updated estimate if available) and the  number of days used for maintenance to determine whether the services  completed aircraft maintenance on time, early, or late. Additionally, we  used the total number of aircraft completed in each fiscal year to calculate  a measure of average maintenance timeliness by aircraft type. We  presented the data based on aircraft that had maintenance completed in  a given fiscal year; however, not all of the maintenance was necessarily  completed in that given fiscal year. For example, an aircraft may have  had maintenance started in one fiscal year and its maintenance was  completed in the next fiscal year. In such a case, we would count that  aircraft in the second fiscal year. In addition, we interviewed DOD and  service officials to gain a better understanding of factors influencing fixed- wing aircraft maintenance timeliness and reviewed our prior work on  depot maintenance.

For objective two, we collected information on the depot maintenance  planning processes for Air Force and Navy fixed-wing aircraft. Using the  non-generalizable sample of 18 Air Force and 18 Navy types of fixed- wing aircraft identified in objective one, we analyzed data on maintenance  duration for maintenance completed in fiscal years 2014 through 2019,  and compared the number of days planned for maintenance to the  number of days used for maintenance to determine the extent to which  planned and actual numbers aligned. We interviewed DOD, Air Force,  and Navy officials to obtain their views on any challenges related to  planning, incorporating historical data, and coordinating with stakeholders  related to the maintenance requirements planning process for aircraft  depot maintenance. For specific challenges identified in the Navy, we  reviewed documents including Naval Air Systems Command (NAVAIR)  workload standards, applicable Navy guidance, and the Navy depot  maintenance strategic plan. We also interviewed Commander, Fleet  Readiness Centers (COMFRC) and NAVAIR officials to determine the  extent to which the Navy incorporates historical data into the maintenance  requirements planning process and the extent to which Navy depot  stakeholders communicate and collaborate to inform this planning  process. In addition, we visited one Air Force aviation depot and one  Navy aviation depot to interview officials from specific aircraft programs,  depot production, and depot business offices to understand any  challenges associated with planning for depot maintenance.

To assess the reliability of the maintenance timeliness and planning data  collected for both objectives, we reviewed and evaluated two systems— one for the Air Force and one for the Navy—that are used to collect and  track data on depot maintenance. We conducted these assessments by  interviewing officials regarding their data-collection processes, reviewing  related policies and procedures associated with the collection of the data,  examining the data for missing values and other anomalies, and  interviewing knowledgeable agency officials regarding their accuracy and  completeness. Based on our assessments, we determined that the data  used from these systems were sufficiently reliable for the purposes of  summarizing trends in the selected aircraft maintenance timeliness and  planning accuracy for fiscal years 2014 through 2019. A detailed  discussion of our scope and methodology is in appendix I.

We conducted this performance audit from April 2019 to June 2020 in  accordance with generally accepted government auditing standards.  Those standards require that we plan and perform the audit to obtain  sufficient, appropriate evidence to provide a reasonable basis for our  findings and conclusions based on our audit objectives. We believe that  the evidence obtained provides a reasonable basis for our findings and  conclusions based on our audit objectives.

Roles and Responsibilities of Depots and Related DOD Organizations

Depots are government-owned, government-operated industrial  installations that maintain, overhaul, and repair a multitude of complex  military weapons systems and equipment for DOD. The military services  operate 17 depots that perform depot-level maintenance on a wide range  of vehicles and other military equipment, including aircraft, engines,  combat vehicles, ships, and software. Of those, the Air Force operates three Air Logistics Complexes and the Navy operates three Fleet  Readiness Centers for aviation depot maintenance (see figure 1). For the  purposes of this report, we will be referring to them as Air Force and Navy  aviation depots.

The Air Force’s and Navy’s aviation depots operate through the Air Force  and Navy working capital funds. Depot customers are charged for the  anticipated full cost of goods and services. Over the past decade, we  have audited the services’ working capital funds activities related to  carryover, new orders, and revenue that can affect depot maintenance  timeliness. For more information on the services’ working capital funds  depot maintenance activities, see appendix II.

The depots are part of a larger, DOD-wide logistics enterprise that  involves a number of different organizations, which are identified in figure  2 and described below.

Assistant Secretary of Defense for Sustainment. This official serves  as the principal assistant and advisor to the Under Secretary of Defense  for Acquisition and Sustainment on materiel readiness. Among other  responsibilities, the Assistant Secretary of Defense for Sustainment  prescribes policies and procedures on maintenance, materiel readiness  and sustainment support. DOD officials report that the Office of the  Deputy Assistant Secretary of Defense for Materiel Readiness is  responsible for maintenance policy along with the development of a  strategic vision for DOD’s organic depot base. Also, the Air Force and  Navy each has its own logistics or materiel command component, which  provides day-to-day management and oversight of the services’ depots.

Air Force Materiel Command. This command develops, acquires, and  sustains weapon systems and their components, providing acquisition  and life-cycle management services and logistics support, among other  things. The Air Force Life Cycle Management Center within Air Force  Materiel Command is responsible for the life-cycle management of  weapon systems from inception to retirement, with a specific program  office managing each type of aircraft. Air Force Materiel Command works  with the program offices to develop, review, validate and prioritize aircraft  depot maintenance workload requirements and associated funding.

Naval Air Systems Command. This command is responsible for  providing life-cycle support of aircraft, weapons, and systems for the Navy  and Marine Corps including, acquisition, repair and modification, and in- service engineering and logistics support. As with the Air Force, a specific  program office manages each type of aircraft. According to Navy officials,  Naval Air Systems Command (NAVAIR), and Commander, Fleet  Readiness Centers (COMFRC) work with the program offices to plan and  approve the maintenance depot work executed at the Navy aviation  depots, including obtaining fixed-wing aircraft workload requirements and  associated funding.

Information on Selected Air Force and Navy Fixed- Wing Aircraft

The 36 Air Force and Navy fixed-wing aircraft types we selected for our  review ranged from fighters to bombers. These aircraft completed a total  of 4,513 depot maintenance events in fiscal years 2014 through 2019.  See figure 3 for more information.

Air Force and Navy Depot Maintenance Timeliness Has Varied for Selected Fixed-Wing Aircraft with a Range of Factors Affecting Depot Performance

For the selected aircraft in our review, the Air Force completed depot  maintenance on time or earlier an average of 82 percent of the time  during fiscal years 2014 through 2019. However, the Navy completed  depot maintenance on time or early in the same period an average of 52  percent of the time. We found that a range of factors, such as unexpected  repairs and aircraft operating beyond their designed service life, have  affected Air Force and Navy depot maintenance timeliness for fixed-wing  aircraft.

The Air Force Has Generally Completed Depot Maintenance On Time While the Navy Has Not

Our analysis of aggregate depot maintenance data regarding fiscal years  2014 through 2019 shows that:

Air Force aviation depots completed depot maintenance of the  selected fixed-wing aircraft on time or early in 5 of 6 fiscal years. The  annual average percentages for on-time or early-completion  maintenance ranged from 78 to 90 percent. In total, selected Air Force  fixed-wing aircraft have spent 22,572 fewer days in maintenance than  expected since fiscal year 2014.

Navy aviation depots were late in completing depot maintenance of  the selected fixed-wing aircraft for each of the 6 fiscal years. The  annual average percentages for on-time or early-completion  maintenance ranged from 45 to 63 percent. In total, the maintenance  for selected Navy fixed-wing aircraft has taken over 62,000 more days  than expected since fiscal year 2014.

Figure 4 shows the percentage of depot maintenance completed on time  or early, as well as total days of maintenance delays, if applicable, for the  Air Force and Navy.

Analyzing the maintenance timeliness data on a per aircraft basis shows  similar trends. The Air Force completed depot maintenance on average  about 7 days early per aircraft during fiscal years 2014 through 2019,  while the Navy completed depot maintenance on average nearly 55 days  late per aircraft (see figure 5).

In comparing depot maintenance timeliness for specific aircraft types, we  found that timeliness varied for both Air Force and Navy aircraft. For  example, Air Force aviation depots completed individual KC-135 aircraft  maintenance an average of about 28 days earlier than projected and  completed F-15E aircraft maintenance an average of almost 35 days later  than projected. Navy aviation depots completed individual EA-6B aircraft  maintenance an average of about 1 day earlier than projected and  completed F/A-18A-D aircraft maintenance on average about 137 days  later than projected.

Figure 6 shows the average number of days—by aircraft type—that the  Air Force and Navy aviation depots completed maintenance earlier or  later than projected in fiscal years 2014 through 2019.

A Range of Factors Has Affected Air Force and Navy Aviation Depot Maintenance Timeliness

Our prior work has identified multiple factors that contribute to depot  maintenance delays, including the size and skill of the depot workforce,  the condition of weapon systems upon arrival at the depot, the availability  of spare parts, and the condition of the depot’s facilities and equipment,  among others. In addition, all of these factors can be affected by funding  and operational considerations (such as unexpected accidents). DOD  officials have stated that disruptions to funding, to include continuing  resolutions, also affect the ability to conduct depot maintenance. Over  the course of this review, Air Force and Navy officials cited many of these  factors as continuing to affect depot maintenance timeliness while offering  specific details on issues contributing to the trends we identified above.

Air Force’s perspectives on early and late completions: Air Force  officials stated a variety of reasons for completing aircraft maintenance  earlier than projected, including frequent communication between  program offices and depot stakeholders. For example, Air Force  Sustainment Center officials told us that they conduct weekly aircraft  performance review meetings with commanders and senior staff to  provide a comprehensive status update on aircraft maintenance  performance that has occurred since the previous meeting. In addition, on  the KC-135 depot production line, Air Force officials told us they  document tasks that can be done concurrently during a specific phase in  the maintenance process, which has helped them meet their timeliness  targets. Air Force officials from across the sustainment enterprise agreed  that proactive planning for depot maintenance requirements helps the  depots provide the appropriate resources to perform aircraft maintenance.  Officials cited unexpected repairs or shortage of skilled depot maintainers  as reasons for later-than-projected completion of maintenance on an  aircraft.

Navy’s perspectives on late completions: Navy officials stated various  reasons for completing aircraft maintenance later than projected,  including growth in the scope of needed work after the aircraft was  evaluated (e.g., finding damage that required tailored engineering  instructions), a diminishing supply of manufactured parts for aircraft, and  aircraft operating well beyond their designed service life—such as the  F/A-18A-D fighters and C-2A cargo aircraft. In addition to operating F/A- 18A-Ds longer than originally planned, Navy officials stated that they also  had to manage aircraft production delays related to the F-35, which was  scheduled to replace the F/A-18A-Ds.

Navy officials explained that they have implemented a variety of  strategies to improve on-time maintenance. These initiatives primarily  focus on mitigating or reducing maintenance delays in the year of  execution. For example:

Naval Sustainment System initiative: The Navy implemented this  initiative at the beginning of fiscal year 2019, which led to the service  implementing private industry best practices and employing new  strategies such as “swarming,” which refers to many artisans being  put to work on a particular aircraft to expedite completion. The initial  focus of these strategies was on the F/A-18E-F. During a site visit to  Fleet Readiness Center Southwest, officials showed us how the  initiative prompted reconfiguration of workstations—clearing storage  and material areas in the hangar and creating direct line of vision for  maintainers—to maximize an artisan’s time spent on an aircraft.

Tracking depots efficiency: Officials are using a new software program  that enables real-time tracking of the progress of aircraft maintenance,  which they told us has led to improved efficiency because it provides  increased visibility into aircraft with delays. For example, officials  stated over the past 2 years, they have decreased the number of  aircraft undergoing maintenance from 390 in 2017 to about 270  across the aviation depots.

The Air Force Generally Has Accurately Planned for Aviation Depot Maintenance, but the Navy Has Not Fully Addressed Several Planning Challenges

The Air Force has largely accurately planned for aviation depot  maintenance requirements for selected fixed-wing aircraft during fiscal  years 2014 through 2019, but the Navy has not. Both services have  initiatives underway to improve planning for aviation depot maintenance;  however, we identified several planning challenges that the Navy has not  fully addressed, such as not effectively using historical data to establish  accurate planning targets for aircraft depot maintenance packages.

The Air Force Generally Has Accurately Planned for Aviation Depot Maintenance Requirements

Our analysis of Air Force planned maintenance workload data—estimates  of the number of days planned for depot maintenance made 3 years in  advance—found that the Air Force largely accurately planned for aviation  depot maintenance requirements for selected aircraft for fiscal years 2014  through 2019. The difference between the number of days the Air Force  planned in advance that it would need for maintenance and actually  needed has been small and trending downward, from 12 percent in fiscal  year 2014 to 3 percent in fiscal years 2018 and 2019 (see figure 7). Our  analysis shows that, for the 6 fiscal years we reviewed, the Air Force  slightly underestimated the amount of time it needed to complete fixed- wing aircraft maintenance by an average of about 6 days per aircraft.

To accurately plan for aviation depot maintenance, Air Force Materiel  Command officials told us they had implemented three key initiatives  including:

Conducting early inspections: Air Force officials stated that they have  been conducting pre-inspections of selected aircraft a year before  scheduled maintenance to check for unplanned maintenance needs,  and to ensure the availability of parts. Officials stated that the early  inspections can clarify the scope of work and avoid extended delays  in completing maintenance. For example, the Air Force has been  conducting pre-inspections of its KC-135—an aerial refueling  aircraft—by sending Boeing engineers to pre-inspect a sample of KC- 135s that are scheduled for depot maintenance in the following year.  The inspections can inform parts orders with long-lead times and  initiate developing procedures to resolve any new repairs identified  during inspections, Air Force officials stated.

Developing and implementing a new metric: To help measure the  effectiveness of planning, Air Force officials stated that in 2017 Air  Force Materiel Command created a new metric—the Planned  Obligations Weighted for Execution Review—comparing which  customer orders were planned for funding versus which ones actually  received funding. According to Air Force officials, the metric provides  visual information to leaders of the degree of variance between the  planned and actual aircraft that come into the depots for maintenance.  Air Force Materiel Command officials stated that the metric has  helped them identify factors affecting the differences between planned  and actual aircraft entering the depots for maintenance and to adjust  resources when needed to address the workload.

Reviewing planning performance and making adjustments: Air Force  Materiel Command annually conducts a two-phased planning process  to establish the organic Air Force depot-level resources necessary to  support the projected funded maintenance requirements for the next 2  fiscal years. Later, the Air Force conducts an after-action review of the  performance of the planning process. In addition, command  leadership, senior staff, and other members of the aviation depot  community hold weekly performance review meetings and make  necessary adjustments. This includes reviewing visual information  such as standardized charts and graphs that provide the current  status of aircraft undergoing depot maintenance, as well as any  issues they are monitoring.

The Navy Generally Has Not Accurately Planned for Aviation Depot Maintenance Requirements

Our analysis of Navy-planned maintenance workload data—estimates of  the number of days planned for depot maintenance made 3 years in  advance—found that the Navy generally has not accurately planned for  aviation depot maintenance requirements for selected fixed-wing aircraft  for fiscal years 2014 through 2019. We found a trend of underestimating  actual days needed for aircraft maintenance. The difference between the  number of days the Navy planned in advance it would need for  maintenance and the number actually needed ranged from a low of 3  percent in fiscal year 2014 to a high of 69 percent in fiscal year 2018.  However, we found the difference declined to 42 percent in fiscal year  2019. Figure 8 shows the difference between planned and actual work  days for selected Navy fixed-wing aircraft in fiscal years 2014 through  2019.

Our analysis, for the 6 fiscal years that we reviewed, showed that the  Navy underestimated the amount of time it needed to complete fixed-wing  aircraft maintenance by an average of about 55 days per aircraft.

The Navy has acknowledged that it has not accurately planned for depot  maintenance requirements. The Navy conducted risk assessments and  internal control assessments in 2018 and 2019 and found material  weaknesses, such as a trend of underestimating time needed to address  aviation depot maintenance requirements. Specifically, the two risk and  internal control assessments stated that Navy policies for defining,  costing, and executing maintenance did not allow them to correctly  predict cost estimates and duration of depot maintenance. In addition, the  Navy’s 2019 risk and internal control assessment highlighted the need to  improve planning accuracy; the report stated that internal reviews found  workload standards did not accurately capture the required maintenance  and that planned maintenance requirements exceeded depot capacity.

Navy officials stated that they implemented an initiative in fiscal year 2020  to improve maintenance requirements called Performance to Plan. This  initiative is focused on incorporating data collection and analysis to,  among other things, improve forecasts of maintenance period durations  according to Navy documentation. For example, the approach of  Performance to Plan is to incorporate predictive data into planning to  improve forecasts of maintenance period durations, according to the  same documentation. While this initiative is a positive step, it is still in the  early stages of implementation and we identified three reasons that have  in part led to inaccurate planning that the Navy has not fully addressed.

The Navy Has Not Effectively Used Historical Data to Update Maintenance Planning

The Navy measures depot performance using turnaround time as one of  the key timeliness metrics. Turnaround time is the overall duration of the  maintenance cycle, from when the aircraft is inducted into the depot to  when it is provided back to the squadron. According to Navy officials, the  Navy reviews historical data to support the maintenance requirements  planning process in various ways, including adjusting turnaround time  based on historical depot performance.

However, we found that the Navy has not effectively used historical data  to analyze turnaround time—total days planned for depot maintenance  periods—and to update maintenance requirements planning for selected  fixed-wing aircraft. Specifically, our analysis of average turnaround time  for selected aircraft depot maintenance packages shows that the Navy  has not adjusted maintenance planning effectively to account for the  actual days needed to perform maintenance. Figure 9 shows that the  Navy kept planned turnaround time the same or with minimal changes for  maintenance packages for the C-2A, the F/A-18A-D, and the F/A-18E-F,  despite worsening trends in maintenance execution during fiscal years  2014 through 2019.

C-2A: In fiscal years 2016 through 2019, the Navy did not adjust its  planned turnaround time—270 days—while the average number of  actual work days to complete maintenance increased from 451 days  in fiscal year 2016 to a high of 722 days in fiscal year 2018. Further,  the difference between the average planned turnaround time and the  average actual number of days needed to complete maintenance  increased from 181 days in fiscal year 2016 to 352 days in fiscal year  2019, and peaked at 452 days in fiscal year 2018.

F/A-18A-D: In fiscal years 2014 through 2019, the Navy adjusted its  planned turnaround time by a total of 82 days, while the average  number of actual work days to complete maintenance increased from  148 days in fiscal year 2014 to 694 days in fiscal year 2019, and  peaked to 857 days in fiscal year 2018. In addition, the difference  between the average planned turnaround time and the average actual  number of days needed to complete maintenance increased from 52  days in fiscal year 2014 to 412 days in fiscal year 2019, and peaked  at 629 days in fiscal year 2018.

F/A-18E-F: In fiscal years 2014 through 2019, the Navy adjusted its  planned turnaround time by a total of 28 days, while the average  number of actual work days to complete maintenance increased from  51 days in fiscal year 2014 to 92 days in fiscal year 2019. In addition,  the difference between the average planned turnaround time and the  average actual number of days needed to complete maintenance  increased from 10 days in fiscal year 2014 to 23 days in fiscal year  2019, and peaked at 59 days in fiscal year 2016.

Naval Air Systems Command Workload Standards Required for the  Aircraft and Engine Programs at the Fleet Readiness Centers states that  COMFRC should analyze and review naval aviation proposed workload  standard packages and compare to actual production and historical  data. It also states that the workload standard development process,  which includes the estimation and development of turnaround time—is to  provide a basis for the identification of resource requirements at the naval  aviation depot, such as personnel skills mix and materials, and as a  budgetary justification of workload for the repair of aircraft. In addition, the  Navy 2014-2019 Depot Maintenance Strategic Plan states that NAVAIR  and COMFRC will identify and sustain requisite core maintenance  capabilities through a planning process that effectively estimates and  monitors near and long-term workload.

Navy officials explained that they have worked to incorporate historical  data into their maintenance requirements planning process; however,  they acknowledged that planning needs to improve and they are in the  process of revising how COMFRC and NAVAIR determines planned  turnaround time. For example, COMFRC and F/A-18 program office  officials said as part of the Naval Sustainment System initiative, COMFRC  is moving toward a 60-day fixed turnaround time on some F/A-18E-F  depot maintenance packages in an effort to drive depot maintenance efficiency and, ultimately, improve aircraft mission capability rates.  According to officials, they plan to apply a fixed turnaround time across all  aircraft. As the Navy moves forward, it must ensure that it effectively uses  historical data to analyze turnaround time and establish accurate  turnaround time targets for fixed-wing aircraft depot maintenance  packages. If it does not do so, the Navy will likely continue to  underestimate the number of days required to perform depot  maintenance and misalign the resources and funding needed at the  depots to perform aircraft maintenance, which in part contributes to  persistent maintenance delays that reduce the time aircraft are available  for operations and training.

Navy Depot Planners Do Not Have Direct Visibility of Maintenance Performed Outside Aviation Depots

We found that Navy depot maintenance planners do not have direct  visibility into fixed-wing aircraft maintenance that is performed outside the  Navy aviation depots by an operational unit or at an intermediate  maintenance facility—information critical to planning for the condition and  depot maintenance needs of individual aircraft. Navy officials said that  data exists on maintenance conducted on an aircraft outside the Navy  aviation depots—by an operational unit or at an intermediate  maintenance facility—and on the condition of an aircraft while deployed  with squadrons. However, depot planners do not have direct visibility over  squadron-level information because the Navy has not provided depot  planners regular reporting on fixed-wing aircraft maintenance performed  outside the aviation depots. Instead, depot planners can access that data  only through a request to the squadron and typically rely on general  planning factors rather than aircraft-specific data when estimating  maintenance needs.

According to Navy officials, the lack of direct visibility into the condition  and maintenance history of an aircraft has driven maintenance delays in  the past. For example, COMFRC and F/A-18 program office officials said  that high turnaround time on certain F/A-18A-Ds undergoing maintenance  was due to extended squadron usage on the aircraft combined with a lack  of logistics support to address these issues. Furthermore, for aircraft  damage that was outside of the depot’s repair capabilities, long lead  times on parts procurement and extensive engineering analysis resulted  in aircraft being placed in delay for extended periods of time, sometimes  years, according to the officials. Figure 10 shows an F/A-18 undergoing  depot maintenance at a Navy aviation depot.

In other cases, high usage by squadrons can cause unexpected corrosion  on many types of fixed-wing aircraft that depots have not prepared to  address. For example, Office of the Chief of Naval Operations officials  said that some aircraft have panels that are taken off during depot  maintenance events. If depot maintainers find unexpected corrosion  behind a panel, it may require additional time to repair that aircraft,  resulting in an increase in the turnaround time. In addition, a COMFRC  official stated an AV-8B arrived at an aviation depot without the engine  installed, which prevents full operational checks being performed during  disassembly. Once maintenance was completed, the aircraft went  through operational checks and officials found canopy seal issues, which  could have been identified if the depot had received data from the  intermediate-level maintenance facility.

The Navy 2014-2019 Depot Maintenance Strategic Plan states that  NAVAIR and COMFRC will identify and sustain the necessary capabilities  to perform maintenance through a planning process that effectively  estimates and monitors near and long-term workload. Navy officials said  direct visibility into data on the current condition and maintenance history  of an aircraft at the squadron level better prepares COMFRC and  NAVAIR to more accurately plan aircraft depot maintenance. This has  been corroborated by Naval Sustainment System initiative findings that  revealed that the Navy should be better informed about the condition of  aircraft in order to improve their maintenance requirements planning.

However, depot planners do not have direct visibility over squadron-level  information because the Navy has not provided depot planners regular  reporting on fixed-wing aircraft maintenance performed outside the  aviation depots. Without regular reporting on fixed-wing aircraft  maintenance performed outside the Navy aviation depots by an  operational unit or at an intermediate maintenance facility, depot planners  cannot plan for the condition and depot maintenance needs of individual  aircraft, which in part contributes to persistent maintenance delays that  reduce the time aircraft are available for operations and training.

The Navy Does Not Have Formal Processes and Guidance for Communication and Coordination between Depot Stakeholders to Inform Maintenance Planning

We found that the Navy does not have formal processes and related  guidance for communication and coordination between depot  stakeholders to inform maintenance requirements planning. Navy officials  explained that depot maintenance stakeholders communicate in a variety  of ways to inform maintenance requirements planning. For example, the  Navy conducts annual and mid-year workload planning meetings. At the  annual workload planning meeting, COMFRC and aircraft program leads  provide plans to meet aircraft workload requirements for the current year  and the next 2 fiscal years. The mid-year review provides an update on  the current year’s performance and the final workload plan for the next 2  fiscal years, according to Navy documentation. Various aircraft program  office leads attend both the annual and mid-year planning meetings to  provide an update on workload plans—among others—to COMFRC.  Navy officials stated that they also informally communicate in a variety of  ways to inform maintenance requirements planning. For example, depot  maintenance engineers may find extra corrosion on an aircraft, and use  those findings to update maintenance plans for other individual aircraft.

While these meetings provide opportunities for collaboration and officials  utilize other means to informally communicate, NAVAIR and COMFRC do  not have formal processes and related guidance for communication and  coordination between depot stakeholders to ensure they receive input  from all key subject-matter experts regarding workload planning. Navy  officials noted that not having formal processes and related guidance  presents several challenges including:

Navy officials said that there is no formal process or guidance for  communication and coordination, and that the process instead  involves a series of documents that COMFRC receives that are  assembled to create a representation of future workload from the  Commander, Naval Air Forces and from each of the aircraft program  offices, among others. A COMFRC official said that different  stakeholders manage various parts of workload planning and without  guidance on specific documentation needs and process owners, it is  challenging for the Navy to identify accountable stakeholders and  discuss specific planning needs.

NAVAIR officials said workload planners hold periodic meetings, but  attendance by subject-matter experts is not mandatory. For example,  subject-matter experts from the Fleet Support Teams—officials who  provide engineering and logistics technical support to fleet and  aviation depot maintenance organizations—are not required to attend  workload planning meetings. Experts may potentially attend via video  teleconference, but others, due to time zone differences, may not  participate. As a result, workload planning meetings may not  consistently include workload input from all relevant subject-matter  experts.

Navy officials said that once the Naval Sustainment System initiative  began focusing on improving depot maintenance on the F/A-18E-F,  deficiencies in the workload planning process became more apparent.  They noted the challenges of coordinating key stakeholders along the  maintenance planning timeline and its impact on planning and  budgeting. In particular, Navy officials stated the current depot  maintenance planning-time horizon was disconnected from long- range planning, such as the Program Objective Memorandum  process. For example, due to a misalignment in the planning and  budgeting processes, COMFRC reacts to the outcome of the Program  Memorandum Objective process rather than influencing it, which  results in many adjustments to their productions plans, such as  improper staffing, material management, and facility-usage plans.

NAVAIR Instruction 5221.1B, Workload Acceptance states that  commanders will establish internal competency guidelines for  communication and coordination of workload-related issues. In addition,  the Navy 2014-2019 Depot Maintenance Strategic Plan, states the Navy  will forge a strong liaison between maintenance activities and the  acquisition community to ensure that maintenance requirements and  planning are in sync. As a result of the Naval Sustainment System  initiative, Navy officials said that COMFRC is developing a new workload  planning process to become more proactive in depot maintenance  planning and increase information exchanges. This includes ensuring that  the new process involves all key depot maintenance stakeholders, such  as COMFRC officials, program managers, and fleet officials. For  example, NAVAIR officials said that most of the Fleet Support Team  scheduled maintenance leads will be the primary point of contact to assist  COMFRC with developing the future maintenance requirements planning  and will be invited and asked to attend workload planning meetings. If  they are unable to attend, they will then ask to have a program office  representative attend in their place.

However, Navy officials acknowledged that their efforts are still in the  developmental stages and that the Navy needs formal processes and  related guidance for communication and coordination between depot  stakeholders to inform maintenance requirements planning. Without these  in place, the Navy cannot be assured that all subject-matter expert input  is proactively solicited and incorporated into depot workload planning,  which in part can contribute to persistent maintenance delays that reduce  the time aircraft are available for operations and training.

The ability of the Air Force and Navy aviation depots to complete  maintenance on time directly affects military readiness. Poor planning for  depot maintenance contributes to longer delays and reduced unit  readiness. The Air Force has generally accurately planned for aviation  depot maintenance over the last 6 years and in turn has completed the  vast majority of its depot maintenance on time or early over this  timeframe. In contrast, the Navy has not accurately planned for aviation  depot maintenance over the last 6 years and in turn has completed only  half of its depot maintenance on time over this timeframe, which has  adversely affected aircraft availability.

While the Navy has implemented an initiative to improve maintenance  planning, the Navy has not effectively used historical data to analyze  turnaround time and establish accurate planning targets for aircraft  maintenance packages. In addition, Navy depot planners do not have  visibility into aircraft maintenance that is performed outside the depots by  an operational unit or other maintenance facility—information critical to  planning for the condition and depot maintenance needs of individual  aircraft. The Navy also has not established formal processes and related  guidance for communication and coordination between depot  stakeholders to ensure they receive input from all key subject-matter  experts to inform maintenance planning. Without addressing these  challenges, the Navy cannot appropriately plan for depot maintenance  workload and may continue to experience maintenance delays that  reduce the availability of aircraft for operations and training.

We are making three recommendations to the Department of Navy.

The Secretary of the Navy should ensure that Naval Air Systems  Command and Commander, Fleet Readiness Centers effectively use  historical data to analyze turnaround time and establish accurate  turnaround time targets for fixed-wing aircraft depot maintenance  packages. (Recommendation 1)

The Secretary of the Navy should ensure that Commander, Naval Air  Forces and Commander, Naval Air Force, Pacific provide depot planners  regular reporting on fixed-wing aircraft maintenance performed outside  the Navy aviation depots by an operational unit or at an intermediate  maintenance facility to ensure they have information on the current  condition and depot maintenance needs of individual aircraft.  (Recommendation 2)

The Secretary of the Navy should ensure that Naval Air Systems  Command and Commander, Fleet Readiness Centers establish formal  processes and related guidance for communication and coordination  between depot stakeholders to inform maintenance requirements  planning. (Recommendation 3)

We provided a draft of this report to DOD for review and comment. In  written comments on a draft of this report, DOD concurred with all three of  our recommendations. DOD’s comments are reprinted in their entirety in  appendix III. DOD also provided technical comments, which we  incorporated as appropriate.

We are sending copies of this report to the appropriate congressional  committees, the Secretary of Defense, and the Secretaries of the Navy  and Air Force. In addition, the report is available at no charge on the GAO  website at http://www.gao.gov.

If you or your staff has any questions about this report, please contact  Diana Maurer at (202) 512-9627 or maurerd@gao.gov or Asif A. Khan, at  (202) 512-9869, or khana@gao.gov. Contact points for our Office of  Congressional Relations and Public Affairs may be found on the last page  of this report. GAO staff that made key contributions to this report are  listed in appendix IV.

Senate Report 115-262 accompanying a bill for the National Defense  Authorization Act for Fiscal Year 2019 included provisions for us to  examine the Department of Defense’s (DOD) aviation depots and  maintenance operations. Our report examines the extent to which 1) the  Air Force and Navy aviation depots completed selected fixed-wing aircraft  maintenance on time from fiscal years 2014 through 2019, and 2) the Air  Force and Navy accurately planned for depot maintenance requirements  for selected fixed-wing aircraft from fiscal years 2014 through 2019 and  addressed any associated challenges. We have separate ongoing  reviews to examine maintenance timeliness and related issues at the  Army and Marine Corps key weapons systems depots and Navy  shipyards.

For objective one, we selected a non-generalizable sample of 18 Air  Force and 18 Navy fixed-wing aircraft types, including fighters, bombers,  and aerial refuelers, based on information from Navy and Air Force  maintenance data and our prior work. These aircraft had maintenance  completed in fiscal years 2014 through 2019, at the Navy’s three Fleet  Readiness Centers and the Air Force’s three Air Logistics Complexes.  We selected this time period so we could identify and obtain insight on  historical data trends regarding maintenance timeliness for the selected  aircraft.

For each aircraft, we collected data on the date maintenance began and  was completed for individual aircraft, as well as the original estimate of  time (in days) needed to complete maintenance. We also collected  updated estimates if available. We used this information to calculate the  difference between the number of days planned for maintenance (using  the updated estimate if available) and the number of days used for  maintenance in order to determine whether the services completed  aircraft maintenance on time, early, or late.

Additionally, we used the total number of aircraft completed in each fiscal  year to calculate a measure of average maintenance timeliness by aircraft  type. We presented the data based on aircraft that had maintenance  completed in a given fiscal year; however, not all of the maintenance was  necessarily completed in that given fiscal year. For example, an aircraft  may have had maintenance begun on it in one fiscal year and its  maintenance completed in the next fiscal year. In such case, we would  count that aircraft in the second fiscal year. The aircraft types we selected  were:

T-6B Texan II Turboprop  In addition, we interviewed DOD and service officials to gain a better  understanding of factors influencing fixed-wing aircraft maintenance  timeliness and reviewed our prior work on depot maintenance.

For objective two, we collected information on the depot maintenance  planning processes for Air Force and Navy fixed-wing aircraft. Using the  non-generalizable sample of 18 Air Force and 18 Navy fixed-wing aircraft  identified in objective one, we analyzed data on maintenance duration for  maintenance completed in fiscal years 2014 through 2019, and compared  the number of days planned for maintenance to the number of days used  for maintenance to determine the extent to which planned and actual  numbers aligned. We interviewed DOD, Navy, and Air Force officials to  obtain their views on the challenges related to planning, incorporating  historical data, and coordinating with stakeholders related to the  maintenance requirements planning process for aircraft depot  maintenance. For specific challenges identified in the Navy, we reviewed  documents including Naval Air Systems Command (NAVAIR) workload  standards, applicable Navy guidance, and the Navy depot maintenance  strategic plan and interviewed Commander, Fleet Readiness Centers  (COMFRC) and NAVAIR officials to determine the extent to which the  Navy incorporates historical data into the maintenance requirements  planning process and the extent to which Navy depot stakeholders  communicate and coordinate to inform this planning process. In addition,  we visited one Air Force aviation depot and one Navy aviation depot to  interview officials from specific aircraft programs, depot production, and  depot business offices to understand challenges associated with planning  for depot maintenance.

To assess the reliability of the maintenance timeliness and planning data  collected for both objectives, we reviewed and evaluated two systems— one for the Air Force and one for the Navy—that are used to collect and  track data on depot maintenance. We conducted these assessments by  interviewing officials regarding their data-collection processes, reviewing  related policies and procedures associated with the collection of the data,  examining the data for missing values and other anomalies, and  interviewing knowledgeable agency officials regarding their accuracy and  completeness. Based on our assessments, we determined that the data  used from these systems were sufficiently reliable for the purposes of  summarizing trends in selected aircraft maintenance timeliness and  planning accuracy for fiscal years 2014 through 2019. We also assessed  the reliability of the working capital fund data related to aviation depot  maintenance activities included in Appendix II, by (1) reviewing our prior  work to determine if there were reported concerns with Air Force and  Navy budgetary data, and (2) reconciling the working capital fund data  that was previously published in our reports for consistency. Based on  our assessment, we determined that these data were sufficiently reliable  for the purposes of presenting information on the services’ working capital  funds activities and budget estimates for fiscal years 2014 through 2019.

Appendix II: Air Force and Navy Working Capital Funds Used for Aviation Depot Maintenance Activities

The U.S. military use working capital funds to procure and provide certain  materiel and commercial products and services to its forces. A Working  Capital Fund (WCF) is a type of revolving fund that operates as a self- supporting entity conducting a regular cycle of businesslike activities,  such as acquiring parts and supplies, equipment maintenance,  transporting personnel, research and development. Department of  Defense (DOD) WCFs are authorized under 10 U.S.C. § 2208 and their  amounts are generally available until expended. Ongoing WCF  operations and maintenance of a minimum cash balance are funded  through reimbursements to the WCF comprised of customer payments for  goods or services received from WCF-supported activities, such as Navy  and Air Force aviation depots. DOD WCFs operate on a break-even  basis, although they may realize gains or losses within each fiscal year.  As part of the annual budget submission for each upcoming fiscal year,  however, prior year gains and losses are taken into account when new  rates are established at levels estimated to recover the budgeted costs of  goods and services, including all general and administrative overhead  costs. Regardless, WCFs must maintain a net-positive cash balance at all  times.

Section 2464 of title 10 of the United States Code requires DOD to  maintain a core depot-level maintenance and repair capability that is  government-owned and operated. Maintaining this capability provides a  ready and controlled source of technical competence and resources to  enable effective and timely response to mobilizations, contingencies, or  other emergencies. Additionally, DOD must assign these government- owned and operated facilities (the depots) sufficient workload to ensure  cost efficiency and technical competence during peacetime, while  preserving the surge capacity and reconstitution capabilities necessary to  fully support the strategic and contingency plans prepared by the  Chairman of the Joint Chiefs of Staff.

The three Air Force and three Navy aviation depots operate through the  Air Force and Navy working capital funds. Depot customers are charged  for the anticipated full cost of requested goods and services. We  reviewed the Air Force’s and the Navy’s budget estimates for fiscal years  2014 through 2019 and describe the information at a summary level  below:

Carryover (funded maintenance work leftover at the end of the fiscal  year): Both services’ aviation depots underestimated carryover for  most years during fiscal years 2014 through 2019.

New orders (funded workload customers place at the aviation depots  for maintenance work to be performed on their aircraft): Both services  generally underestimated the amount of funds that their aviation  depots received from new orders placed by customers and the work  performed did not keep pace with those orders from year to year,  during fiscal years 2014 through 2019.

Revenue (dollar amount of work performed by depots in a single  fiscal year): The services have varying trends for revenue for fiscal  years 2014 through 2019. In fiscal years 2014 and 2017 through 2019  the Air Force, and for fiscal years 2014 through 2017 the Navy,  overestimated the amount of revenue that was actually earned.  Conversely, the Air Force underestimated for fiscal years 2015  through 2016, and the Navy underestimated during fiscal years 2018  through 2019.

Workload (workload projections are expressed in Direct Production  Earned Hours (DPEHs) for the Air Force and Direct Labor Hours  (DLHs) for the Navy): A DPEH or DLH is an hour earned by a direct  employee against an established work order, and includes civilians,  contractors and military personnel. In fiscal years 2014 through 2019,  Air Force depots’ workload increased from 21,337,000 DPEHs to  24,511,000 DPEHs—an increase of about 3.2 million (14.9 percent)  DPEHs. During those same years, Navy depots’ workload generally  increased from 10,161,000 DLHs to 11,668,000 DLHs—an increase  of about 1.5 million (14.8 percent) DLHs.

Personnel (civilian and military personnel performing depot  maintenance at aviation depots and civilian staff performing support  functions, such as finance and budgeting and supply and  acquisitions): In fiscal years 2014 through 2019 the number of civilian  personnel working at the aviation depots has generally increased by  around 3,000 for both the Air Force and the Navy.

Each year, customers order billions of dollars of maintenance work that  the depots cannot complete by the end of the fiscal year. To the extent  that the depots do not complete work at year-end, the work and related  funding will be carried into the next fiscal year. DOD refers to this  reported dollar value of work that has been ordered and funded  (obligated) by customers, but not completed by working capital fund  activities at the end of the fiscal year as “Carryover”.

DOD allows and the congressional defense committees recognize that  some carryover from one fiscal year to the next is needed to ensure a  smooth flow of maintenance work during the transition from one fiscal  year to the next. However, past congressional defense committee reports  have raised concerns that the level of carryover may be more than is  needed. DOD has reported that approximately 6 months of carryover is  optimal. Excess carryover (i.e., more unfinished work than allowed) may  reflect an inefficient use of resources and tie up funds that could be used  for other priorities. Excessive amounts of carryover may result in future  appropriations or budget requests of depot customers being subject to  reductions by DOD and the congressional defense committees during the  annual budget-review process. Tables 1 and 2 show Air Force and Navy  carryover for fiscal years 2014 through 2019, respectively.

Accurate budgets for the amount of new orders to be received by the  depots are essential for them to plan their work, such as determining the  right number of personnel, parts, and material needed. For example, if the  services include workload in their new order estimates that do not  materialize, a depot is at risk of incurring unplanned financial loss  because the depot is allocating its overhead costs over less work than  planned. These losses may lead the depots to increase their rates for  repairing assets. If the customer receives more funding (e.g., Operations  & Maintenance or Procurement) than they originally anticipated and they  in turn increase their orders with the depots (new orders or just an  increase to an existing order), or if operational decisions lead to changes  in requirements or priorities, unplanned workload may materialize at the  depots resulting in additional carryover. Tables 3 and 4 show Air Force  and Navy new orders for fiscal years 2014 to 2019, respectively.

Revenue represents the dollar amount of work performed by depots in a  single fiscal year. DOD WCFs conduct businesslike activities to generate  revenue from the sale of goods or services to customers, such as the  military services or combatant commands, to cover costs expended  throughout the year in support of those services. The DOD FMR 7000.14- R directs DOD WCFs to operate on a “break-even” basis (revenue  generated equals the cost associated with receiving the revenue). See  tables 5 and 6 for Air Force and Navy Depots’ Revenue (Budgeted vs  Actual) for fiscal years 2014 through 2019.

The Air Force and Navy express depot workload projections in Direct  Production Earned Hours (DPEHs) for the Air Force, and Direct Labor  Hours (DLHs) for the Navy. A DPEH or DLH is an hour earned by a direct  employee against an established work order in the performance of depot  work on an end item. The Air Force and Navy include direct labor hours  worked by civilians, contractors and military personnel in their DPEH and  DLH projections. Tables 7 and 8 show Air Force DPEHs and Navy DLHs  for fiscal years 2014 through 2019, respectively.

The number of civilian personnel at the Air Force and Navy aviation  depots—referred to as end strength—perform the majority of depot-level  maintenance activities and are made up of personnel such as artisans  and maintainers—welders, machinist, sheet metal mechanics, aircraft  mechanics, aircraft electricians, engineers and scientists—performing  aviation depot maintenance, but also includes personnel performing  support functions such as finance and budgeting. Tables 9 and 10 show  total civilian and military personnel employed at the Air Force and Navy  aviation depots for fiscal years 2014 through 2019, respectively. As seen  in table 9, in fiscal years 2014 through 2019, the number of civilian  personnel working at the Air Force aviation depots has grown by over  3,000 civilians (25,540 to 28,576). As seen in table 10, in fiscal years  2014 through 2019, the number of civilian personnel working at the Navy  aviation depots has grown by over 3,100 civilians (8,515 to 11,643).

Appendix III: Comments from the Department of Defense

Appendix IV: GAO Contacts and Staff Acknowledgments

Diana Maurer at (202) 512-9627 or maurerd@gao.gov, or   Asif A. Khan at (202) 512-9869 or khana@gao.gov.

In addition to the contacts listed above, Chris Watson (Assistant Director),  Delia Zee (Analyst-in-Charge), John Craig, Sergio Enriquez, Amie Lesser,  Felicia Lopez, Amanda Manning, Keith McDaniel, Richard Powelson,  Benjamin Sclafani, Michael Silver, and Roger Stoltz (Assistant Director)  made key contributions to this report.

Military Depots: DOD Can Benefit from Further Sharing of Best Practices  and Lessons Learned. GAO-20-116. Washington, D.C.: January 30,  2020.

Navy Maintenance: Persistent and Substantial Ship and Submarine  Maintenance Delays Hinder Efforts to Rebuild Readiness. GAO-20-257T.  Washington, D.C.: December 4, 2019.

Naval Shipyards: Key Actions Remain to Improve Infrastructure to Better  Support Navy Operations. GAO-20-64. Washington, D.C.: November 25,  2019.

F-35 Aircraft Sustainment: DOD Faces Challenges in Sustaining a  Growing Fleet. GAO-20-234T. Washington, D.C.: November 13, 2019.

Depot Maintenance: DOD Should Adopt a Metric That Provides Quality  Information on Funded Unfinished Work. GAO-19-452. Washington, D.C.:  July 26, 2019.

Military Depots: Actions Needed to Improve Poor Conditions of Facilities  and Equipment That Affect Maintenance Timeliness and Efficiency.  GAO-19-242. Washington, D.C.: April 29, 2019.

DOD Depot Workforce: Services Need to Assess the Effectiveness of  Their Initiatives to Maintain Critical Skills. GAO-19-51. Washington, D.C.:  December 14, 2018.

Navy and Marine Corps: Rebuilding Ship, Submarine, and Aviation  Readiness Will Require Time and Sustained Management Attention.  GAO-19-225T. Washington, D.C.: December 12, 2018.

Navy Readiness: Actions Needed to Address Costly Maintenance Delays  Facing the Attack Submarine Fleet. GAO-19-229. Washington, D.C.:  November 19, 2018.

Depot Maintenance: DOD Has Improved the Completeness of Its Biennial  Core Report. GAO-19-89. Washington, D.C.: November 14, 2018.

Air Force Readiness: Actions Needed to Rebuild Readiness and Prepare  for the Future. GAO-19-120T. Washington, D.C.: October 10, 2018.

Weapon System Sustainment: Selected Air Force and Navy Aircraft  Generally Have Not Met Availability Goals, and DOD and Navy Guidance  Need to Be Clarified. GAO-18-678. Washington, D.C.: September 10,  2018.

F-35 Aircraft Sustainment: DOD Needs to Address Challenges Affecting  Readiness and Cost Transparency. GAO-18-75. Washington, D.C.:  October 26, 2017.

Naval Shipyards: Actions Needed to Improve Poor Conditions That Affect  Operations. GAO-17-548. Washington, D.C.: September 12, 2017.

Depot Maintenance: Executed Workload and Maintenance Operations at  DOD Depots. GAO-17-82R. Washington, D.C.: February 3, 2017.

Depot Maintenance: Improvements to DOD’s Biennial Core Report Could  Better Inform Oversight and Funding Decisions. GAO-17-81. Washington,  D.C.: November 28, 2016.

Army Working Capital Fund: Army Industrial Operations Could Improve  Budgeting and Management of Carryover. GAO-16-543. Washington,  D.C.: June 23, 2016.

Defense Inventory: Further Analysis and Enhanced Metrics Could  Improve Service Supply and Depot Operations. GAO-16-450.  Washington, D.C.: June 9, 2016.

Navy Working Capital Fund: Budgeting for Carryover at Fleet Readiness  Centers Could Be Improved. GAO-15-462. Washington, D.C.: June 30,  2015.

Army Industrial Operations: Budgeting and Management of Carryover  Could Be Improved. GAO-13-499. Washington D.C.: June 27, 2013.

Marine Corps Depot Maintenance: Budgeting and Management of  Carryover Could Be Improved. GAO-12-539. Washington, D.C.: June 19,  2012.

Air Force Working Capital Fund: Budgeting and Management of  Carryover Work and Funding Could Be Improved. GAO-11-539.  Washington, D.C.: July 7, 2011.

Three Air Force and three Navy aviation depots maintain critical aircraft such as the KC-135 tanker and F/A-18 fighter. Delays at depots can reduce aircraft availability for operations and training.

We reviewed depot performance for selected aircraft over 6 years.

Air Force depots completed maintenance on-time or early in 5 of 6 years (with aircraft in maintenance 22,572 fewer days than expected)

Navy depots were late all 6 years (over 62,000 more days than expected)

We also identified Navy planning challenges, such as a need for more effective use of historical maintenance data. We made 3 recommendations to the Navy to reduce delays.