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 maintenance personnel.

Pulling one specific circuit breaker, which is labeled, would render inoperative both of the 777's transponders, according to documents reviewed by The Wall Street Journal and bolstered by comments from aviation industry officials and those who have worked with the 777.

Becoming familiar with the 777's systems requires extensive training for pilots and aircraft mechanics alike, experts said. However, considerable technical data on the airplane is also available online in discussion groups or other websites.

Investigators are trying to establish a sequence of events that transpired on the jet, which vanished from radar March 8, most critically the loss of communication.