B747-400
Communication Breakdown; Time Pressure; Troubleshooting
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Procedure; MEL; Human Factors
An incorrect deferral was issued for a malfunctioning Tank-4 Forward (Fwd) Fuel Boost Pump. During cockpit prep; the Tank-4 Fwd Fuel Boost Pump switch light was not illuminated; as it should be with the pump 'Off'; indicating that there was pump pressure with the switch 'Off.' There was EICAS confirmation [of fuel pressure] with the lack of an Engine # 4 EICAS Fuel pressure message; as there should be and like there was for Engine/Tank-1. The Mechanic said it was a faulty Pressure switch on the Tank-4 Fwd Pump System. But there was an Engine-4 Fwd Pump 'On;' when commanded 'Off' error in the Central Maintenance Computer (CMC). The Mechanic erased it; recycled the System; Circuit Breakers (C/B); and switches. The message came back to the CMC; and the light indications returned; indicating that the pump was running when it [the fuel pump] should be 'Off.' He said he was going to defer the Pressure switch; so we could leave. The Captain agreed; but I continued to advocate that he needs [Maintenance to] troubleshoot the malfunctioning [fuel] pump; not the pressure switch. A faulty pressure switch would not extinguish the Engine-4 Fuel Pressure EICAS message because it is on the other side of a one way valve in the fuel system and would not cause a fuel pump 'On' when commanded to the 'Off' position. CMC message. Errors: Procedural; problem with other Company Policy/ Procedures.
Reporter stated he was quite upset with Maintenance Control for deferring the Pressure Switch for the Tank-4 Forward Fuel Pump pressure light indication. The light would not illuminate (show low fuel pressure indication) when the pump switch was positioned to 'Off'. Since the APU was running at the gate; Maintenance suspected fuel manifold backpressure was not allowing the Tank-4 pressure light to illuminate normally. The Horizontal Stab fuel tanks were empty. There was a lack of adequate troubleshooting to determine if; in fact; the Tank-4 Forward Fuel Pump would shut-off with the 'On-Off' switch. The Pressure switch could be deferred; but the Fuel pump was a 'No-Go' item if the pump could not be shut-off with the switch. Reporter stated that was the second time on their B747-400 aircraft that he has experienced a similar problem where the Fuel Boost Pump Pressure switch would not shut-off the fuel pump. On that aircraft; the flight was canceled and the fuel pump replaced; which corrected the discrepancy.
A First Officer explains why he believes an incorrect deferral was applied to a B747-400 aircraft for a malfunctioning Tank-4 Forward Fuel Boost Pump Pressure indication light not illuminating; when the pump switch was positioned to 'Off.'