B757 flight crew experiences a MCP malfunction at lift off that causes erratic changes to all parameters controlled by the Mode Control Panel. This malfunction included numerous uncommanded engagements of the autopilot. After declaring an emergency the flight returns to departure airport for a raw data ILS in IMC to a safe landing.
Synopsis
B757 flight crew experiences a MCP malfunction at lift off that causes erratic changes to all parameters controlled by the Mode Control Panel. This malfunction included numerous uncommanded engagements of the autopilot. After declaring an emergency the flight returns to departure airport for a raw data ILS in IMC to a safe landing.
Narrative
On gear retraction the captain's flight director bars disappeared. I cycled the F/D switch but they did not return. The First Officer's bank steer bar disappeared but his pitch bar was in view. My FMA and the First Officer's FMA did not agree and all of the lights on the mode control panel were flickering on and off as if being pushed. As we were handed off to Departure we were given an altitude and heading change. The heading read 251 and was uncontrollable. The altitude had been preset to 5;000 but read 2;300 and was uncontrollable. The airspeed read 6 and was uncontrollable. The orange airspeed bug slewed randomly from 162 KTS to 350 KTS before settling on 350 KTS for the duration of the flight. As we were dealing with this the autopilot warning sounded and illuminated. I asked the First Officer why he had engaged the autopilot and he stated that it had engaged uncommanded and that he was disengaging it (the autopilot engaged uncommanded at least 10 times during the 14 minute flight). Concerned about flight control issues and a potential electrical fire I declared an emergency with ATC; sent a message to Dispatch stating our intentions to return to ZZZ; and called the Purser to give him a cabin advisory. An uneventful approach and landing ensued and after being inspected by rescue we then proceeded to the gate under fire escort. All appropriate checklists were accomplished.
Second reporter narrative
Just after takeoff the aircraft experienced numerous MCP and Flight Mode Annunciation anomalies. Airspeed bug on Airspeed instrument fluctuated between 160 KTS and 350 KTS. The autopilot came on without being commanded. I clicked off the autopilot. I also deselected the auto-throttles with the throttle switches and asked the Captain to turn off auto-throttle switch on MCP. I also switched off the Flight director. The Captain asked ATC for immediate return to ZZZ and declared an emergency. The Captain notified the company and briefed the flight attendants on the situation. While flying downwind I estimate the autopilot engaged itself between 5 and 10 times. Each time I would disengage autopilot with yoke switches. The MCP was unresponsive to inputs and airspeed bug continued to fluctuate. We flew a hand flown raw data ILS in IMC conditions to an uneventful landing and rollout. After crash and rescue looked aircraft over; we taxied to the gate.
NASA callback
The Captain reports that the aircraft was returned to service after Maintenance replaced the MCP and the aircraft was test flown. The aircraft was dispatched with the external power receptacle on MEL for unknown reasons; which might have had some bearing on this incident but exactly what is unknown.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.