777 MCP Altitude Window Changing Without Pilot Action
Remember that Boeing Bulletin.... 'To inform flight crews that the altitude in the MCP altitude window may change indication without pilot action'? Never personally saw it happen but according to the bulletin..... 'An operator has experienced multiple occurrences of the MCP altitude window indication changing by 1000, 1500, 2000, and 4000 foot increments during climb, cruise, and descent. These changes occurred without flight crew input to the MCP. In addition when operating in VNAV, the altitude indication has changed after the altitude selector was pushed.'
Then the bulletin said...."Initial findings suggest that electrostatic discharge introduced when the pilots touch the MCP may be causing the value in the altitude window to change."
But when I attended a Boeing symposium, if I understood correctly, they said that they were leaning toward the theory that it was caused by the occasional random cosmic ray. Imagine that...a random highly charged atomic particle passing through the airplane and possibly leading to an altitude violation.