Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue
Flight Crew Returned To Gate; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft
Aircraft was pushed back and crew cleared to start engines. The Before Start Checklist was called for to 'Below the Line'. The checklist was complied with and completed. Upon review; the 'Fuel Pumps-On' was still 'white' and reflecting that the fuel pumps were not sensed 'on'. Upon review; we were in agreement that the checklist looked like it had been properly complied with and that the fuel pumps were indeed on. We were in agreement that this was not a normal situation; and that we didn't want to try to 'force' the checklist to look complete. Company Dispatch; Maintenance and Operations were all brought into the loop. It was agreed upon to tow the aircraft back to the gate to try to make sense as to why the Before Start Checklist was not sensing complete; primarily in regard to why the fuel pumps were not sensed 'on'. The flight was ultimately cancelled as no one; at the time; could determine why the fuel pumps were not apparently working the way we expected them to. I don't know why this event occurred. There has been a discussion; relayed by the Captain; that perhaps the fuel load had the center wing level at an amount that perhaps created a situation where the Center Pumps would appear to be needed by the crew when the 'aircraft' thought they should be off. Having sat through the entire event and witnessed nearly all of the Maintenance effort and diagnosis; I am left puzzled with no clear knowledge as to why the checklist didn't reflect completed; enabling us to start the engines and complete the flight.If what was discussed re the fuel level in the center tank being the issue (pumps on v pumps off); then perhaps a caution or highlighted discussion should be given to the crews about this situation developing should be given. Is it or isn't it an issue?
We pushed back from the gate. Set the brakes and was finishing the before start checklist. The First Officer got to the line item FUEL PUMPS ON which was highlighted white and would not go green after turning on all main and center tank fuel pumps. Our release fuel and load was 87;100 lbs; full wings and around 12;000 lbs. in the center tank. We took a look at the pump switch configuration and found all 4 main tank and center tank pumps selected ON. We then elected to try resetting the pump switches off then on 3-4 cycles to correct what we thought might just be an erroneous sensing by the computer controllers system logic. No changes. We then called Dispatch and got a phone patch to Tech Services and asked for assistance to figure out and fix the problem. They ran various telemetries and noticed that the left fwd-right fwd and aft pumps had all load shed giving us the indication of no pressure output from the pumps in the ON selection. We tried further resets of the main pumps as they were showing no pressure output and it seemed to everyone involved (crew & Tech Services) that it had something to do with the Electronic Checklist not being able to clearly sense an item complied with and being unable to move forward on the that line item. Further data showed that the APU was powering the airplane and was nowhere near its maximum power ability or demand which also confused the situation for load shed and Tech services ran out of ideas to explain the situation so we returned to the gate and called Contract Maintenance; who arrived and took over the situation. They worked with Tech services for hours until the flight crew ran out of duty time and then called the flight. It was my understanding that they would continue the troubleshooting with Tech services through the night. The next day I called Maintenance Control to find out the status of the airplane and was told it was ready for service.Apparently unbeknownst to us all (crew; Tech services; contract maintenance ) it was normal for the load shed situation during the before start checklist. We all saw the pressure lights ON on the 3 main tank pumps and assumed there was a problem (fuel pump to provide pressure for engine start) and troubleshot the issue as such. Maintenance and Tech services figured out the issue the following morning and returned the aircraft to service.In flight manual Volume one it states 'NOTE-PRESS lights may be illuminated until after engine start because of load shedding'. We all assumed it was due to the center tank pumps being load shed until after engine(s) start as they are override pumps to distribute the center tank fuel first. For those of us who flew previously the 767 and 777 that had this type of system; it seemed normal to us and that it was very odd to get a main tank fuel pump load shed during engine start; especially with APU loads with comfortable limits; a good amount of fuel in the center tank; and not having noticed the fuel pump pressure indications. Maintenance and Tech services had the same opinion. During further troubleshooting they verified that the pumps were operational but not finding any documentation that the load shed scenario was correct and continued to troubleshoot for a fault in the system(s). Eventually they received information regarding this issue from Boeing that produced a document that pressure lights would be on and load shed normal. It was also discovered in B-787 Operations manual volume II fuel system description page 12.20.1-12.20.2 that 'when less than all engines/generators are operating; there may not be sufficient electrical power to operate all pumps. In such cases; the fuel system automatically determines the best pumps to operate depending on how much electrical power is available. Certain pumps may load shed until enough electrical power is available. The indications that a fuel pump has load shed are that the pump switch PRESS light is illuminated and the pump is labeled LOAD SHED on the fuelsynoptic. It also was pointed out in 787 Operating manual volume I; before start checklist expanded page NP 3.1.5 'If FUEL IN CENTER EICAS msg is displayed: CENTER FUEL PUMP SWITCHES-ON.' I also had a conversation with Captain Y; Boeing 777/787 Tech pilot who informed me of an issue Boeing discovered with the airplane that if you have around 12;000 lbs of fuel in the center tank it can cause issues with the system logic to display the FUEL IN CENTER MSG accurately for reasons unknown at this time. He also said Boeing had previously had this 12;000 lb fuel figure in the manual but for reasons favoring the EICAS msg (FUEL IN CENTER) it was deleted from the manual. In this event; we had been planned with a release fuel of 87;100 lbs which after deducting the wing fuel would leave around 12;000 lbs of fuel in the center tank. If an anomaly occurred as per the information shared by Captain; it would fit the scenario that happened to us that night as we had all main tank pumps selected and center tank pumps. If the airplane logic for whatever reason did not detect the 12K of fuel in the center to display the FUEL IN CENTER EICAS msg. it would not allow that the fuel pumps on line item to be sensed normal and completed and allow the line item to go from white to green and let one move on with the rest of the checklist. The next day I instructed dispatch to plan the fuel to have at least 15;000 lbs in the center tank to avoid this anomaly . We tested the situation before departure and found all had worked normal an as described. All these mentioned events occurred and caused much confusion to the crew; Maintenance; and Tech services and made for a difficult situation to resolve in a timely manner. I also believe there may be issue on how this is described in the manuals that can be inadequate or confusing to both pilots and Maintenance. The above mentioned 12;000 lb center tank fuel anomaly should be mentioned and elaborated in pilot and maintenance manuals. Until a resolution is found; fuel should be planned by Dispatch to stay away from that 12;000 lb figure in the center tank- either stay below/above it 2000-3000 lbs as we did on the flight back to ZZZ. Make it a Hot Item for 787 initial and recurrent training.
B787 flight crew reported a gate return due to fuel transfer pump operation impeding completion of the engine start checklist.