Airbase sortie generation analysis model (ABSGAM)
RIGHTS OF THE GOVERNMENT 
     The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to a method used to predict the maximum sortie generation capability of aircraft operating from a typical air base, and more particularly to a method for use during the analysis phase of a vehicle design, to critique different features for their impact on performance. In addition, the method could be used to evaluate commercial transport systems such as trucking, shipping, airline/cargo, space transport, and auto rental; either the evaluation of existing vehicles or of new designs. 
     Different areas such as aircraft supportability, maintainability, and survivability and airbase survivability come together to influence the sortie generation capabilities of an aircraft. An aircraft force is armed and fueled for a mission. The mission is flown during which the aircraft are either damaged, attrited, returned for maintenance, or are immediately placed in the mission capable pool. This mission capable pool of aircraft is then armed and fueled for the next sortie. In evaluating the effectiveness of weapon system designs, it is desirable to stimulate the process. The simulation model should permit the user to change input parameters to evaluate their effect on: (1) aircraft sortie rates, (2) cumulative sorties generated, (3) payload launched, and (4) material/personnel required to support the air base operation. 
     Previously, the analysis and graphical representation of data was performed by hand. The process was slow and tedious, was a poor utilization of resources, and was time consuming. This hand analysis and graphics approach, combined with a normal limit on manpower, resulted in a limited study scope and understanding. On the other hand, there are known systems using large, complex sortie generation analysis code, but they are too expensive, manpower wise, for a small office (5 to 50 people) to operate, and generally take the full time support of 1 to 3 people, take 2 to 6 months to learn, require expertise in disciplines outside the scope of the study, and require a large mainframe computers. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a means to quickly and efficiently analyze the sortie generation capabilities and support requirements of vehicle designs and to perform effectiveness analyses on these designs, particularly for aircraft. A further object is to fill the gap between a simple, hand sortie generation analysis; and a large, complex sortie generation analysis code. More generally, an object is to provide a meanns for vehicle system effectiveness analysis. 
     The invention relates to a method, using a computer model, refered to as an Airbase Sortie Generation Analysis Model (ABSGAM) to predict the maximum sortie generation capability of aircraft operating from a typical air base. The model allows the user to easily change input parameters to evaluate their effect on: (1) aircraft sortie rates, (2) cumulative sorties generated, (3) payload launched, and (4) material/personnel required to support the air base operation. ABSGAM simulates (1) an air-base-attack and recovery, (2) reduced payload operations, (3) reduced maintenance capability, (4) extended turn-around time, and (5) aircraft attrition (both air and ground). Program input has been minimized for ease of use. Program output is available in tabular and graphical form. 
     Advantages 
     This software provides a quick and efficient means of analyzing the sortie generation capabilities of vehicle designs. The program is designed for easy use by requiring minimal user inputs. The built-in graphics capability provides high quality data plots and a much improved insight and understanding of the dynamic trends of the analysis. The user may select from eleven plotting options to display the data output. This allows the program to be used as a real time study tool--generating parametric trends, sensitivities, and trade-offs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a block diagram which shows how the different areas such as aircraft supportability, maintainability, and survivability and airbase survivability come together to influence the sortie generation capabilities of an aircraft; 
     FIG. 2 is a diagram which illustrates this process in a logical sequence: 
     FIG. 3 and FIGS. 3a-3g inclusive are flow charts of the computer program; and 
     FIGS. 4 and 5 are a tabular chart and a graph respectively which illustrate an example of the outputs of the program. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     During the analysis phase of a vehicle design, different features are critiqued for their impact on performance: in particular, the sortie generation capabilities of the aircraft. FIG. 1 shows how the different areas such as aircraft supportability, maintainability, and survivability and airbase survivability come together to influence the sortie generation capabilities of the aircraft. FIG. 2 illustrates this process in a logical sequence. An aircraft force is armed and fueled for a mission. The mission is flown during which the aircraft are either damaged, attrited, returned for maintenance, or are immediately placed in the mission capable pool. This mission capable pool of aircraft is then armed and fueled for the next sortie. The Airbase Sortie Generation Analysis Model (ABSGAM) simulates the process. FIG. 3 is a flowchart of the computer program. FIGS. 4 and 5 illustrate an example of the tabular and graphical outputs of the program, respectively. 
     In FIG. 1, the Airbase Sortie Generation Analysis Model (ABSGAM) is represented by the dashed block 10, which models the airbase flight operations represented by block 12. The output includes sortie rate, number of sorties and payload delivered versus time. Inputs for the model include the aircraft design and misson performance requirement (block 14) which provides input to block 15 on required takeoff and landing performance, and landing gear dynamics. Block 16 shows base maintenance and aircraft battle damage repair capability, aircraft reliability, turn around time, and attrition and battle damage. Block 17 provides the airbase attack schedule, used as input to block 18 on airbase recovery, such as crater repair. Blocks 15, 16 and 18 supply inputs to the block 12. 
     Note that the landing gear system is analyzed for its dynamic load response to a runway surface roughness outside of the ABSGAM. A particular design will have a maximum surface roughness that it can traverse without exceeding the limit load capability of the aircraft. The time to repair a runway is a direct function of this roughness level (Civil Engineering standards for repair). Thus, for a given airbase attack scenario, the times to first damage and then repair of a runway can be calculated. These two times are input into the ABSGAM model, and represent both the landing gear capability and the Civil Engineering repair capability. 
     Landing gear characteristics were required for a special case in a study. Generally, other design characteristics would be used. The exact characteristics would depend upon the particulars of the study being performed. 
     1.0 INTRODUCTION 
     A program listing in FORTRAN is included as part of this patent application. 
     The following description is taken from a technical memorandum AFWAL-TM-87153 (hereinafter &#34;said tech memo&#34;-a copy in draft form is included with this patent application as filed, and is hereby incorporated by reference), which is the user&#39;s manual for a computer model developed to predict the maximum sortie generation capability of aircraft operating from a typical USAF air base. The model, entitled &#34;Air Base Sortie Generation Analysis Model (ABSGAM),&#34; allows the user to easily change various input parameters to evaluate their impact on: (1) aircraft sortie rates, (2) cumulative sorties generated, (3) payload launched, and (4) material/personnel required to support the air base operation. ABSGAM stimulates: (1) an air-base-attack and recovery, (2) reduced payload operations, (3) reduced maintenance capability, (4) extended turn-around time, and (5) aircraft attrition (both air and ground). Program output is available in graphical and tabular form. 
     The purpose of this project was to assess the military worth of some selected, advanced technologies on future aircraft designs and subsystems. These technologies include five advanced landing gear concepts, onboard chemical-biological detoxification equipment, and low-profile crew modules. A series of advanced, deep-strike fighters were designed to evaluate the various technologies. The sortie generation capability of the strike fighter operating with each of five landing gear candidates was analysed. ABSGAM was developed to enhance this analysis. 
     The above paragraph is specific to one study. The computer program is generalized so that other technologies can be evaluated (not just landing gear). 
     2.0 SORTIE GENERATION MODEL 
     The sortie generation model is based on several assumptions which are &#34;hard-wired&#34; into the computer code. This approach minimizes the input required by the user and simplifies the program. If desired, the program could easily be modified to allow these values to be user-defined. However, this modification would complicate the program and the input required by the user. The &#34;hard-wired&#34; values were defined by &#34;off-line,&#34; or hand studies. These studies included development of the maintenance cycles and the air-base-attack and recovery modes. Other input variables are user-defined and include force size, mission time, required mission fuel, and the desired engagement length. 
     The model stimulates an entire mission (sortie) cycle for a user-defined number of aircraft. A sortie is flown, during which some aircraft are attrited or damaged. After the mission, aircraft enter maintenance and repair cycles if necessary, while the mission-capable aircraft are rearmed/refueled for the next sortie. The model simulates a maximum 30-day flight operation. FIG. 2 represents the basic sortie generation model. The initial force is shown as a circle 20. At the beginning of a sortie, block 22 shows the step of rearming and refueling and when ready going to block 24 for flying the sortie. The model makes various counts and supplies data on number of aircraft damaged to block 26  for battle damage repair, number of aircraft failed to block 27 for maintenance, number of aircraft available, and number of aircraft lost to block 28 for attritted aircraft. From this data the number of mission capable aircraft is determined for the next sortie. 
     2.1 CASE 1-NO AIR-BASE-ATTACK 
     A normal flying day of 0600 to 2000 hours was defined. At 0600, all mission-capable aircraft enter a rearming/refueling cycle. (This pre-flight cycle was defined as the first event of the day in order to simplify the program). The user inputs the mission air time, the fuel required per sortie, and the aircraft weapons load. The program calculates the time required to prepare (rearm/refuel) the aircraft for the mission. This calculation is based on six (6) rearming stations (typical for an air base), a rearming time of ten (10) minutes/aircraft (estimated for advanced weapons and loading techniques), six (6) refueling stations (typical for an air base), a refueling rate of 600 gallons/minute (one of two primary flow rates used by NATO), and a three (3) minute taxi time between the rearming and refueling stations. These hard-wired values were fixed for this study, but the program could be modified to accept values input by the user. 
     After all mission-capable aircraft have completed the rearm/refuel cycle, a mission is launched with all available aircraft. During the mission, aircraft are attrited due to combat at a rate defined by the user. (The user defines a combat attrition rate for each of the 30 days). 
     Aircraft that survive the mission enter a damage repair cycle, a maintenance cycle, or are immediately declared mission-capable. The number of damaged aircraft to attrited aircraft is assumed to be a 3:1 ratio. The damaged aircraft require 24 hours to repair before becoming mission-capable. The number of aircraft requiring general maintenance is determined by the user-defined critical mean time between failure (MTBF). Aircraft requiring maintenance enter a 2 hr, 8 hr, 24 hr, or extended (10-day) repair cycle. Of the aircraft entering maintenance, 39% require 2 hours of maintenance before being declared mission-capable, 39% require 8 hours, 19% require 24 hours, and the remaining 3% require 10 days of maintenance. These percentages were developed through a comparison of MTBF&#39;s for the existing U.S. force structure and the maintenance required by each type of aircraft. Maintenance is performed 24 hrs/day. The mission-capable aircraft are added to the aircraft returning from maintenance (required after previous missions) to determine the total number of mission-capable aircraft available for the next mission cycle. The rearm/refuel time is calculated for this sum of aircraft. If the aircraft can be armed and fueled and a mission launched before 2000 hrs, the model will execute the sortie even though the aircraft may return well after the set day end (2000 hrs). 
     2.2 CASE 2-With Air-Base Attack 
     ABSGAM has a built in air-base-attack and recovery capability. When this capability is used, the model simulates two 3-day attack sequences on the base. The base is attacked and forced to close at 0530 on each of the six (6) attack days. At a user-specified time for each day, a taxiway is opened as a minimum operating strip (MOS). The MOS has limited operational capability; however, and missions launched from this strip have a reduced payload per aircraft. This reduced payload allows the aircraft to take off within the available length and smoothness of runway surface. For example, the level of runway quality needed for flight operation is dependent upon the landing gear concept being evaluated in this case. When the main runway is reopened at a later, user-defined time, full payload is resumed. For each attack sequence, the user inputs the times (for each of the 3 days) that the taxiway is opened, the reduced payload for each day, and the day and time that the main runway is reopened after the 3-day period. The attack days hardwired into the program are days 1, 2, 3, 13, 14,  and 15. The program could be modified to accept user-defined attack days; however, reprogramming the 3-day attack concept would require a larger modification of the program. This attack and recovery scenario was built up from existing threat data and its postulated attack concepts. 
     The program also accounts for the effects of an attack on maintenance and rearm/refuel times, and includes ground attrition due to the attack. Ground attrition due to the attacks is calculated using 3%, 1.5%, 0.5%, 1.5%, 0.75%, and 0.25% of all remaining aircraft at the beginning of days 1, 2, 3, 13, 14, and 15, respectively. No maintenance is performed on aircraft from the time the base is attacked on the first day of a 3-day attack period until the main runway reopens. It is assumed that all ground personnel (except preflight crews) would be devoted to recovering the runways. The maintenance cycle times are then increased by 1/3 after the main runway reopens following the first 3-day attack and are doubled (2X normal) after the main runway reopens following the second 3-day attack. Thus the 2-hr maintenance cycle may become a longer cycle after an attack. The user should note that the headings on the output will not change. The user should realize that, after the first attack, the  2-hr maintenance cycle is actually longer than two hours. The rearm/refuel time is doubled (2X normal) when the main runway is closed. It is increased by 1/4 when the main runway reopens after the first 3-day attack and is increased by 1/2 (1.5X normal) when the main runway reopens after the second 3-day attack. These increases reflect the damage to support facilities sustained in the attacks. 
     2.3 SIMPLE PROGRAM FLOWCHART 
     The simple flow chart of FIG. 3 shows a start block 30, followed by setting a run number counter to I=O at block 32. Block 34 shows the input to define input and case parameters. At block 36 a run is executed, followed by tabular output at block 38. At decision block 40 the user is given the option to plot results, and if the response is yes, the graphical output is produced at block 42. 
     ABSGAM offers the user the option of restarting after a run is completed. For example, after a run, the user can restart the program, change any number of input parameters or files, and re-execute. After each run, the user has the option of plotting the results of any combination of previous runs on a single graph. This capability allows the user to perform trade studies on the input parameters, compare peacetime/wartime scenario results, or compare different aircraft configurations, and then display the different results of several runs on a single plot. The program is dimensioned to allow the user up to 10 runs per program execution. This restart option is illustrated in the simple program flowchart at block 44. another run is chosen, the run number is incremented at block and then returned to block 34 for input. If this was the last run, the program goes from block 44 to stop at block 48. 
     3.0 PROGRAM DESCRIPTION AND USAGE INSTRUCTIONS 
     A more detailed flow chart is shown in FIGS. 3a-3g, corresponding to the FORTRAN listing at the end of this specification. The connectors in circles of the flow chart correspond to line numbers in the listing, or to connectors between pages. On the first two pages, the program listing defines a list of variables and allocates memory, represented in FIG. 3a by the Start block 100. 
     At block 100, the flow chart shows opening the print file `SG.PRINT`, which is file 9 in the listing. This file will collect all non-graphics screen output and user inputs. A file 1 is used in the listing to read input from the keyboard and to write or echo to the monitor screen. 
     Block 115 shows initialization of the program execution counter (RUN) to zero. 
     Block 120 shows the definition of days when the base is under attack. Missions may be skipped on these days. Block 120 also shows that values are provided for the reduced maintenance factor array and the reduced rearm/refuel array for the two three-day attacks. Section 2.2 above gives further information relative to this block. 
     The program at block 125 asks the user if this will be an air-base-attack case. 
     AIR BASE ATTACK CASE (Y,N) 
     This option is provided on every run, enabling the user to run an air-base-attack case and non-air-base-attack case and to compare the results within the same execution of the program. The user responds with either a Y or an N. 
     If the response at block 126 is N, as shown at block 130, the program sets all attack days to zero for a non air base attack case, and sets an attack counter (A) to three. The reduced maintenance and rearm/refuel factors are set to one. The operation then goes to line 25. 
     If the response is neither N nor Y, the operation returns via line 4 to block 120 to repeat the request. 
     If the air-base-attack case is chosen, the program will at block 135 prompt the user for an air-base-attack input filename. 
     INPUT AIR BASE ATTACK FILENAME 
     The user responds with the name of a directory file. The length of this filename can be up to nine (9) characters. The user must generate this file and will typically have an air-base-attack file for each aircraft configuration or attack scenario being studied. This file includes an air base open time and reduced payload capacity for each of the six days the base is under attack, and the day and time that the main runway reopens after each 3-day attack period. Each line of data is unformatted, and the file contains eight (8) lines, as in the following example: 
     2153 2 
     1914 2 
     1914 2 
     2153 2 
     1914 2 
     1914 2 
     6 0830 
     18 0830 
     At block 140, the program reads the runway open time from the identified input file, and reads the runway open time and reduced payload for missions completed during the attack days. At block 145 the program initiates the attack counter (A) and takes the reduced maintenance and rearm/refuel factors from the arrays. At block 150, the program reads the day and attack time when the main runway opens after each 3-day attack, and then converts these times to minutes from day 1 time 0000 in military format. 
     The attacks occur on days 1, 2, 3, 13, 14, and 15 (this is hard-wired into the program). Using the air-base-attack file shown above, the base reopens at 2153 on days 1 and 13, and at 1914 on days 2, 3, 14, and 15. (The program always assumes the base is attacked and closes at 0530 on each of the six attack days). Any missions completed on these days have a reduced payload capacity of two weapons. (The full payload capability is included among the main input parameters.) The main runway reopens on days 6 and 18 at 0830. The reduced payload for the third day of each 3-day attack is used until the main runway reopens, at which time full payload capability is resumed. 
     For both the not attack and attack cases, the program goes via line 25 to block 160 of the flow chart, to increment the program execution counter, and then via line 8 goes to block 200 of FIG. 3b. 
     The user has three options when providing the main input parameters for the program. The program at block 200 asks the user whether these parameters will be entered interactively, through file input, or by modifying the input of a previous run. 
     INPUT 1 FOR INTERACTIVE INPUT 
     INPUT 2 FOR FILE INPUT 
     INPUT 3 FOR MODIFICATION OF PREVIOUS RUN 
     Block 201 of the flow chart indicates the response. 
     If the user chooses interactive input (1), the program at block 205 prompts him as follows: 
     **INPUT NUMBER OF AIRCRAFT IN INITIAL FORCE** 
     **INPUT ENGAGEMENT LENGTH IN DAYS** 
     **INPUT MISSION FLIGHT TIME IN MINUTES** 
     **INPUT AIRCRAFT MTBF IN HOURS** 
     **INPUT FUEL REQUIRED (LBS FUEL/SORTIE)** 
     **INPUT MAINTENANCE MAN-HOUR RATE (MMH/FH)** 
     **INPUT MAX PAYLOAD (NO. OF WEAPONS)** 
     For each prompt, the user should enter a value for that variable. 
     If the user selects the file input option (2) the program goes to block 210 and, the file &#34;SG.INPUT&#34; must be located in the directory. This file consists of one line of unformatted data, as follows: 
     
         72 30 90 7.5 26000 25. 10 
    
     These values correspond to: 
     (1) number of aircraft in the initial force 
     (2) engagement length in days (maximum of 30) 
     (3) mission flight time in minutes 
     (4) aircraft critical mean time between failure (MTBF) in hours 
     (5) fuel required in 1 lbs fuel per sortie 
     (6) maintenance man-hours per flight hour 
     (7) maximum payload capacity per aircraft 
     If the user chooses to modify the previous run, as shown at block 215, the input data for the previous run is retained, so that the user may change the parameter(s) desired. In all three options the program goes via line 7 to block 220, where, the input data is echoed to give the user a last chance to change any parameter before beginning a run. 
     ENTER NUMBER AND NEW VALUE OF VARIABLE TO BE CHANGED 
     (EXL 1.72) 
     1-NUMBER OF AIRCRAFT IN INITIAL FORCE-30 
     2-ENGAGEMENT LENGTH IN DAYS-30 
     3-MISSION FLIGHT TIME IN MINUTES-90 
     4-AIRCRAFT MTBF IN HOURS-7.500 
     5-FUEL CONSUMPTION RATE (LBS FUEL/SORTIE)-26000 
     6-MAINTENANCE MAN-HOUR RATE (MMH/FH)-25.0 
     7-MAX PAYLOAD PER MISSION (NO. OF WEAPONS)-10 
     0-(ANY NUMBER) DATA IS CORRECT? 
     At block 225, the program then reads the number (NVC) and value (VNV) and at block 226 checks whether the number (NVC) is zero. If not the new value is entered at block 230, and the flow returns via line 7 to block 220. 
     After the input of the main parameters is completed, the user types O followed by any number to continue. The program goes via line 41 to block 235, to store the run variables in print matrices. The program at block 300 of FIG. 3c then prompts the user for a filename containing daily combat attrition rates. 
     INPUT ATTRITION RATE FILENAME 
     The length of the attrition rate filename can be up to 12 characters. The user could save any number of attrition files (peacetime, wartime, high, low, etc.) in the file directory and run comparison studies by making similar runs with different attrition files. At block 305, the program opens, reads and closes the attrition rate file. An attrition rate file consists of six (6) lines with five (5) values per line (unformatted) as shown. 
     
         ______________________________________                                    
.0465     .0460     .0450     .0434   .0410                               
.0370     .0325     .0260     .0205   .0170                               
.0141     .0123     .0110     .0097   .0088                               
.0080     .0075     .0070     .0065   .0062                               
.0059     .0058     .0057     .0056   .0055                               
.0055     .0055     .0055     .0055   .0055                               
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     The 30 values above are percent attribution rates for each of the 30 days in the simulation. These values, when multiplied by the number of aircraft flying a mission, provide the number of aircraft attrited during that mission. 
     At block 310, the program will initialize variables for cumulative attrition, daily attrition, missions skipped due to an attack and no print flags, day counter, daily sorties, cumulative sorties, fuel consumed and maintenance man-hours per flight-hour, current payload capacity, cumulative payload, daily payload, available aircraft, and ground attrition rates. 
     At block 315, the program calculates the maintenance rate as the flight time divided by the mean time between failures in minutes (MAINRAT=FLTIME/MTBF*60). 
     If the aircraft mean time between failures is less than the mission length, aircraft will be gained during the maintenance cycle. To eliminate this problem, the program at block 320 checks the maintenance rate, and if it is greater than one (input MTBF is less than the mission length), the flow returns via line 7 to block 220 in FIG. 3b for the MTBF to be set equal to the mission length. If the MTBF is equal to or less than one, the program goes to block 325. 
     A maintenance and damage pointer is initialized at LM(I)=1. for I=1 to 5. A normal day start time is defined as MSTART=360. A timer is started (TIME=MSTART). The program writes an output heading for the first day. 
     The program then begins executing the missions and outputs the results in a table and summary for each day of the engagement. 
     3.1. Main Loop 
     In FIG. 4d at block 400, the program then begins the main loop to be executed for every mission. The mission number MI is initially set to one. The maximum value of 350 is greater than would occur in any simulation run. 
     At block 405 a check is made as to whether the number of available aircraft variable is less than zero, and if so, is set to zero. 
     At block 410, the attack counter A is checked whether it is less than or equal to two (this counter was either set to three at block 130 for non-attack cases, or initially set to one at block 145 for attack cases). If the base has been attacked, a check is made at block 415 as to whether the main runway is ready to reopen by a comparison of the current time against the variable for time of day the main runway opens after each three-day attack. A negative result from either of blocks 410 or 415 causes the program to go to block 425. 
     If the base has been attacked and the main runway is ready to reopen, the flow chart goes to block 420, to set the payload to full capacity, increment the attack counter, and tell the user that the main runway is now open before executing the next mission. 
     At block 425, a variable is set for the next engagement day; and at block 430 this variable is checked to determine if it is one of the six attack days built into the program. If the base is under attack, a check is made at block 435 to see if a flag has been set indicating that missions have already been skipped. If not the operation goes to block 440 to set variables to reduce the payload capacity, calculate the ground attrition and update the available aircraft. A mission skip routine is executed, and the mission skip flag is set (so same missions are not skipped again next time through the loop. The program will change the mission number and no print option if all missions are skipped this day. Then at block 445, the program checks the time to determine if it is the end of the day, and if so goes to line 32. If block 430 indicates that it is not an attack day, block 435 indicates that missions have already been skipped, or block 445 indicates that it is not the end of the day, the operation goes to FIG. 3e. 
     At block 500, the program calculates the ground time for rearming and refueling, and increments the time. At block 505, if it is the end of a day, the operation goes to line 32. 
     If it is not the end of day, the program proceeds to block 510 to run a mission, which comprises calculating attrited aircraft and the number of sorties; incrementing daily sorties, payload, and attrition; calculating damaged aircraft, surviving aircraft, aircraft requiring maintenance, and mission capable aircraft. The program also determines the time when damaged aircraft and aircraft requiring maintenance after the next mission will be available. It reduces the number of available aircraft by the number of damaged aircraft and aircraft requiring maintenance. There are also time calculations and updating. 
     At block 515, the program will test the pool of aircraft in maintenance and damaged aircraft to determine which aircraft will be available for the next mission. The number of available aircraft is increased and a pointer is reset. There is a calculation of the number of aircraft returning from maintenance; and a calculation of the mission start time (converted to military time). 
     The operation now goes via line 32 to block 520 to again check for the end of day. If yes, then at block 530 the program will increment a day counter, reset the mission skip flag, increment the time, test the pool of available aircraft, and add to the number of aircraft available. 
     At a decision block 535 a check is made for an attack day, and if yes goes to block 540 to increment an attack counter and set attack variables. 
     A no response from block 520 or block 535, or completion of the operations of block 540, takes the flow to FIG. 3f. 
     At block 600, all data generated by the most recent mission is written as output to the screen and to the output file. 
     At decision block 605, if it is not the end of day, the program via line 10 goes to block 400 of FIG. 3d to increment the mission counter (MI) and begin the main loop for the next mission (the DO 10 loop begins on page 8 of the listing and the 10 CONTINUE line is at the middle of page 14). If the response from block 605 is yes, operation goes to block 610. 
     After the last mission of the day, the program writes to the screen and to the output file the daily and cumulative attrition; increments the cumulative sorties and payload; outputs the daily and cumulative sorties; outputs the daily and cumulative payload; saves the values for daily and cumulative sorties, daily and cumulative payload, daily and cumulative attrition, and available aircraft for the beginning of the next day. It calculates and saves the daily and cumulative fuel consumption, and daily and cumulative maintenance man-hours. It resets the daily counters for attrition, sorties, payload, and ground attrition to zero. 
     Examples of daily outputs for an attack day and a non-attack day are shown in FIG. 4. For each completed mission, the output includes the following: 
     (1) mission start time 
     (2) aircraft available to fly the mission 
     (3) aircraft attrited during the mission 
     (4) aircraft damaged during the mission 
     (5) total number and breakdown of aircraft entering the four (4) maintenance cycles after the mission 
     (6) the number of aircraft returning from maintenance during this mission that will be available for the next mission 
     (7) the number of aircraft that flew this mission and require no maintenance before flying again 
     The sum of the last two columns equals the available aircraft for the next mission. The last value in the RETN ACFT column represents aircraft that will return from maintenance overnight. A daily operations summary with cumulative totals is provided after the mission data table. 
     At a decision block 615 of FIG. 3f, the number of the day is compared to the number of days for the run, to determine if this is the end of the run. If not, operation returns via line 10 (to FIG. 3d) to run the next mission. 
     After the output for the last day of the engagement, the program at block 620 gives the user the choice of plotting the results of this run and/or any previous runs. (Up to 10 runs may be plotted). 
     DO YOU WISH TO PLOT RESULTS (Y,N) 
     If the user does not want to plot at this time (indicated by N), the program at block 630 gives the user the option of restarting the program or stopping (block 635). 
     RESTART (Y,N) 
     If the user decides to plot (Indicated by a Y response above), the program goes via line 14 to block 625 for the graphics output operation shown in more detail in FIG. 3g. The program calls several subroutines, which are part of a graphics software package. At block 700, the program gives the user eleven (11) types of curves from which to choose: 
     1-DAILY SORTIES 
     2-CUMULATIVE SORTIES 
     3-AVAILABLE AIRCRAFT 
     4-DAILY ATTRITION 
     5-CUMULATIVE ATTRITION 
     6-DAILY FUEL CONSUMPTION 
     7-CUMULATIVE FUEL CONSUMPTION 
     8-DAILY MAINTENANCE MAN-HR 
     9-CUMULATIVE MAINTENANCE MAN-HR 
     10-DAILY PAYLOAD 
     11-CUMULATIVE PAYLOAD 
     0-QUIT 
     INPUT NO OF CURVE TYPE 
     If the user chooses the QUIT option (0), the RESTART (Y, N) prompt (block 710, like block 630) reappears. If the user selects a type of curve, the program at block 715 prompts the user for run numbers to be plotted. A run summary matrix is displayed to help the user with this input. 
     ENTER RUN NOS. TO BE PLOTTED 
     The user responds with the run numbers (previous runs and/or most recent run), separated by commas, to be included in the plots. If the number of runs to be plotted is less than 10 (which will usually be the case), the program will give a MORE prompt. If the user does not wish to have any more runs included, hitting the RETURN key will continue the program. The program at block 720 will define the minimum and maximum values for the X-axis, determine the maximum range of the X-data to be plotted, define the X-data, define the number of points per curve, define the Y-data on the curve chosen by the user, and determine the minimum and maximum values of the Y-data. At block 725 the program shows the user the minimum and maximum values to be plotted on the abscissa and ordinate. 
     THE RANGE IS XXX. XXX. THE DOMAIN IS XXX. XXX. INPUT XMIN, XMAX, YMIN, YMAX 
     The user then inputs the minimum and maximum abscissa and ordinate values to be used to label the plot. (There are always 10 divisions on each axis). 
     The program at block 730 then prompts the user for a title, subtitle, and x- and y-axis labels. 
     INPUT TITLE 
     INPUT SUBTITLE 
     INPUT X-AXIS LABEL 
     INPUT Y-AXIS LABEL 
     The length of each of the titles and labels is limited to 40 characters. 
     After the titles are input, the program at block 735 generates the plot. An example is shown in FIG. 5. The program pauses after the plot is completed to allow the user a chance to review the plot and make a hardcopy if desired. The user needs to hit the RETURN key to continue after the plot is completed. The program returns to the curve type menu via line 14 to block 700, allowing the user to generate a different plot. 
     4.0 Program Input/Output and Execution on the Prime Compute 
     ABSGAM was written for the AFWAL/FIAD PRIME 750 minicomputer, and uses Tektronics Plot 10 IGL Graphics subroutines for the plotting capability. 
     The program requires several files to be located in the user&#39;s directory. These files include the executable version of the program, several small input files, and one output file. ABSGAM.SEG is the executable version of the program. Input files required are: SG.INPUT (only required for the file input option for the major input parameters), an attrition rate input file with a filename up to 12 characters (required in all cases), and an air-base-attack input file with a filename up to nine (9) characters (only required to run an air-base-attack simulation). All non-graphic output (prompts, responses, and program results) that is printed at the terminal is written to SG.PRINT. This provides the user with a hardcopy of the entire execution. 
     A simple CPL (Command Procedure Language) file would be useful for executing the program. A CPL file could be as simple as: 
     DELETE SG.PRINT 
     SEG ABSGAM.SEG 
     If this file is called SG.CPL, the user would type R SG to delete the old output file (SG.PRINT) and execute the program. The new output would overwrite the old output in SG.PRINT if the file was not deleted; however, if the new output is shorter than the old output, part of the old output would remain at the end of the new SG.PRINT file. Therefore, it is wise to delete the old SG.PRINT file before executing the program. 
     ALTERNATIVES 
     The program was originally developed to investigate candidate landing gear technologies. It can also be used to assess other technologies which contribute to aircraft sortie generation (flaps, thrust reversers, V//STOL concepts, battle damage repair, survivability/vulneability features) or to assess airbase survivability features (defense, hardening, redundancy, dispersion, tactical location, recovery). Another alternative use is as a primary tool in a &#34;system&#34; study such as base/aircraft profile, land battle support, logistical requirements, etc. 
     It is understood that certain modifications to the invention as described may be made, as might occur to one with skill in the field of the invention, within the scope of the appended claims. Therefore, all embodiments contemplated hereunder which achieve the objects of the present invention have not been shown in complete detail. Other embodiments may be developed without departing from the scope of the appended claims. 
     The program could be used in the defense industry, and could be adapted for similar design studies. In addition, it could be used to evaluate commercial transport systems such as trucking, shipping, airline/cargo, space transport, and auto rental; either the evaluation of existing vehicles or of new designs. ##SPC1##