Improper fuel management of crossfeed operations during a boost pump failure in Textron Beechcraft King Air 90-series airplanes can cause a dual engine failure, even though usable fuel may remain, according to a new FAA Safety Alert for Operators (SAFO 18001).
In the event of a boost pump failure, the crossfeed function opens automatically and “fuel consumption is double the normal amount from the side with the operating boost pump,” the alert notes. If improper fuel planning allows fuel to be depleted on that side, both engines will most likely flame out, even though usable fuel remains in the tanks on the side of the inoperative pump. “If that happens, options become limited,” the FAA said.
Even if the crossfeed valve is closed manually, the high-pressure fuel pump on the side of the inoperative boost pump might still suction-feed; but if the crossfeed remains open, the fuel pump might instead suction air only through the empty crossfeed line. “There is no engineering data to determine either way,” the SAFO notes. “As such, there is clear risk that a simple boost pump failure, if not managed properly, could result in dual engine failure.”
The SAFO reminds operators that if a boost pump fails, the emergency procedure in AFM directs the pilot to “momentarily close the crossfeed valve to determine which pump failed and then open it again, turning off the failed pump.” The emergency checklist further states, “If continued flight with the crossfeed closed is required, monitor for power fluctuations.”