B757-200
Flight Crew Air Transport Pilot (ATP)
Troubleshooting; Workload; Confusion; Human-Machine Interface; Distraction
Aircraft Equipment Problem Critical; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural MEL / CDL
Flight Crew Overcame Equipment Problem; Flight Crew FLC Overrode Automation; General Maintenance Action
Procedure; Logbook Entry; Aircraft
It was day four of a five-day trip; involving a three-leg flight. After the first leg; the Captain and I spoke briefly with the crew that flew our next assigned aircraft on a previous flight in crew operations. We were briefed the previous crew could not get the aircraft to level off in the VNAV autopilot mode during climbout. They also said the autopilot would not track the localizer or glideslope without excessive deviations. The Captain called Maintenance Control to express our concerns and to learn more about resolution of the discrepancies raised by the previous crew. Our concerns included whether it was actually a VNAV problem; or something more; and if the malfunction was an altitude hold function that could restrict our ability to operate in RVSM airspace. We were also concerned about possible additional fuel requirements because of potential flight at lower altitudes. We met the Local Mechanic at the aircraft and learned the aircraft passed all ground testing that was performed but that the autoland functions were a little weak. The Captain again expressed concern that perhaps more was involved than just the VNAV mode malfunctioning; and that none of the testing performed seemed to point directly to the VNAV mode as the source of the problem raised by the previous crew. The aircraft was then deferred per B-757 MEL 22-11-04-10: Mode Control Panel Switches - VNAV; FLCH; V/S; ALT HOLD Switches - VNAV inoperative; and a deferral sticker was placed on the MCP Panel next to the VNAV switch. This MEL requires 3 of the 4 modes to be operative. Our concern was that one or more of the other modes were implicated in the discrepancy. We accepted the aircraft for the flight. Our departure clearance was the Newark 1 Departure (EWR1) and we planned and briefed an initial climb altitude to 5;000 FT per the EWR1 SID. We specifically briefed FLCH takeoff and climb procedures; and the need for [acceleration and flap cleanup] speeds to be manually selected: 215; 235; and then 250 KTS. Our takeoff clearance; however; included a level off at 2;500 FT MSL; a low altitude level off. After takeoff; the aircraft quickly accelerated up to and through speeds set for the FLCH takeoff. The Captain manually retarded the thrust levers but they advanced again. ATC cleared us to climb to 6;000 but the Flight Management Annunciators (FMAs) indicated ALT CAP and then ALT HOLD even though the MCP altitude had been set to 6;000 before nearing 2;500. When I saw the airspeed quickly accelerate towards our flap limit speed; I said 'watch your airspeed.' At this time the Captain was calling for 'Flaps 1'; then 'Flaps up'; while also trying to manually retard the thrust levers. The Captain then tried to re-engage FLCH and 250 KTS; but the autothrottle advanced the thrust levers to climb power and the aircraft accelerated the aircraft even more. Around this time; I noticed a momentary red flash next to the airspeed tape indicating a flap overspeed. The airspeed I recall seeing; however; was 218 KTS; which is below the flaps 5 limit speed and the flaps were transitioning to flaps 1 or flaps up. I made a call to increase climb. Next; the aircraft continued to accelerate beyond 250 KTS; and at one point reached about 265 KTS; while we were below 10;000. [We experienced] task saturation; failure to timely de-automate; manually fly aircraft and prevent flap and FAR overspeed. [There was a] lack of specific deviation calls as pilot not flying [and] failure of Maintenance to properly identify and repair system discrepancy. I learned as the pilot not flying is to be more descriptive with my deviation calls by specifying the concern regarding a deviation; and also to be more descriptive with my directive/corrective calls. I should have specifically stated; 'approaching flap limit speed'; and/or 'raise your nose'; and/or 'disengage autothrottles'. Also; I would be more specific in a FLCH takeoff brief to include not only MCP procedures (aswe briefed) but also include FMA expectations. Also; I would be quicker to recommend or direct complete de-automation if needed. In this scenario; I never felt safety was compromised and intervention was not contemplated. The Captain was taking affirmative steps to correct an autoflight malfunction brought about by a difficult maintenance discrepancy that was providing deceptive information to us and apparently false information to the autoflight system. Also; the Captain was using the HUD and it seemed to further support the autoflight information being provided which; in this scenario; seemed to be false. The Captain did a terrific job maintaining a safe flight trajectory during a difficult autoflight malfunction during a low altitude level-off at night while using the HUD. Of note; during a subsequent flight with the same aircraft; maintenance deferred the autothrottles per B-757 MEL 22-30-01; thinking that to be the source of the discrepancy. On climbout; however; we were cleared to level off at 12;000. Accordingly; the MCP altitude was set to 12;000. Passing through about 9;000 during a FLCH climb; ALT CAP was displayed on the FMA followed by ALT HOLD. Of course; this improper autoflight information was easier to manage and overcome above 10;000 than it was during a low altitude level-off scenario at 1;000.
Despite attempts by Maintenance to diagnose; identify and disable via MEL malfunctioning autoflight and autothrottle functions; the B757-200 flight crew reporters suffered additional failures of vertical navigation modes and autothrottle functionality after takeoff.