B777-200
Distraction; Workload
Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Aircraft; Human Factors
After level off and stable in cruise at FL330 and Mach .83. (Right side auto throttle placarded inop; left side auto throttle working properly). Right throttle being operated manually and aligned with left throttle; which was engaged and properly maintaining assigned speed. During a busy time; several frequency changes and preparing for our oceanic clearance; aircraft speed reduced to an unacceptable level; operating throttle failed to advance at all and had to be manually overridden; which was done; airspeed returned to acceptable level shortly after correction was made. Flight continued without further problems; throttle were operated manually for the duration of flight.
Cruising at FL330 abeam Madrid. Crew set Mach .83 with operating autothrottle armed and non-operating autothrottle off. Crew set both throttles to maintain .83 Mach. While coordinating Oceanic clearance and both pilots were monitoring different frequencies; the airspeed degraded without being noticed by either crew. An EICAS message alerted crew to low speed flight. Both throttles were advanced to maximum power and aircraft accelerated back to .83 Mach. No altitude deviation was necessary. The operating autothrottle did not advance to maintain airspeed. Crew distraction caused a loss of situational awareness and not catching the degradation of airspeed before the EICAS message warning.When autothrottle is inoperative; it must be briefed; especially during periods when both pilots are conducting separate duties; i.e. Oceanic Clearance; that ONE pilot always monitor the throttles. We both assumed that the operating throttle would advance as necessary to maintain airspeed; this did not happen and caused the airspeed to decay without being noticed. This is a situation that does not happen often when the crew flies with an inoperative autothrottle; and needs to be properly monitored by crew; and not rely on advancement to occur.
B777 Flight Crew reports being dispatched with the right autothrottle inoperative. At FL330 and maintaining Mach .83 the operating autothrottle fails to advance and the crew is alerted to a low speed condition by the EICAS. After recovery manual throttles are used for the remainder of the flight.