Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical
General Declared Emergency
Aircraft
The aircraft had an MEL for 'Main Tank Pumps - Tank 1 Aft Inop'. About 200 miles out from our destination; during cruise; we received an 'ENG 1 SUCT FEED' alert. For some reason the autosystem had shut all the pumps off without providing crossfeed to the engine. We went to manual and back to auto and the system returned to normal ops for about 1 minute before shutting all the Number 1 tank pumps off again. In manual we had the forward pump providing positive pressure; so we went back to manual and continued the flight. Just after initiating the descent; we received a 'Tank 3 Tip Trapped' alert with an accompanying 'TANK 3 FUEL QTY LOW' alert. The aircraft also began to quickly develop an imbalance between tanks 1 and 3. We declared an emergency due to the speed with which the imbalance was developing. The imbalance slowed as we descended. We landed uneventfully.
Dispatched with a deferred inoperative aft fuel boost pump the flight crew of a large commercial fixed wing jet were concerned when the autofuel management system turned off the forward pump as well but did not open a crossfeed to provide positive fuel pressure to the engine. To maintain pressure they went to manual but; approaching top of descent; received a CAS warning of trapped\unavailable fuel which caused them to declare an emergency.