B777-200
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Overcame Equipment Problem
Aircraft
1) Preflight normal; MCP set-up for departure; MCP Speed set at 170 KTS. 2) Aircraft push back from gate. 3) Engine start as per normal procedure. 4) After engine start; Taxi clearance. 5) Moments after; MCP speed window went from 170 to 150 without any human intervention. 6) None of us touched the MCP speed control knob; or any area on the MCP! 7) I reset the MCP speed to 170 KTS. 8) Flight proceeded normally without any other MCP issue. 9) Landed - speed intervene during approach; no other anomaly noted on MCP. 10) Event written up in logbook.None of us touched the MCP speed control knob; MCP panel; or anything else in any way when this event took place - Speed just flipped from 170 to 150 - Not good. An extensive study should be made of the software that controls the MCP display. This is the second event that I personally know about; and it is reported to me that [other airlines] have had similar events. There is definitely a bug in Block Point 14 as it relates to the speed set in the MCP speed window; and it needs to be fixed before this event happens in flight and becomes a causal factor in a catastrophic event.
B777-200 First Officer reported after a normal preflight; and before takeoff; the MCP speed window went from 170 to 150 uncommanded.