If multiple communication systems aboard Malaysia Airlines Flight 370 were manually disabled, as investigators increasingly suspect happened, it would have required detailed knowledge of the long-range Boeing Co. 777's inner workings.

The first loss of the jet's transponder, which communicates the jet's position, speed and call sign to air traffic control radar, would require disabling a circuit breaker above and behind an overhead panel. Pilots rarely, if ever, need to access the circuit breakers, which are reserved for...