ATA 28

Alternate Boost Pump Failure
Your flight crew has called you from a remote location with an apparent failed right alternate fuel boost pump. They would like to know if there is a method to make the main boost pump operate and not scrub the flight. No maintenance services are available at their location. You check the FAA Master Minimum Equipment List (MMEL) and see that dispatch of the aircraft with the failed alternate boost pump is allowed, providing the main boost pump is operable. The problem is the main fuel boost pump won’t come on line without fuel pressure in the manifold.
1) What action may be taken to “force” the on-side main fuel boost pump to run, even though the boost pump control relay is sensing no fuel pressure?
2) Why will this action allow the main fuel boost pump to come on line without fuel pressure present in the engine fuel supply manifold?
3) Considering bus configuration, which engine should be started first to ensure the right main boost pump continues to operate during the right engine start cycle?

Please Note: Although the aircraft may be dispatched with one boost pump inoperative, the flight crew should review the abnormal procedures found in Section III of the Airplane Flight Manual (AFM) as a precaution, should the remaining pump fail during the flight.

Fault Findings
1. The main boost pump can be forced on-line by pulling the alternate boost pump circuit breaker and placing the control switch to main.
2. With the alternate pump circuit breaker tripped, 28 VDC can’t energize the boost pump control relay(BPCR). With this relay de-energized, the main boost pump remote circuit breaker now has a path to ground through the BPCR relay and will operate.
3. Because the right main boost pump remote circuit breaker is powered by the #1 main DC bus, the left engine must be started first.