Missing MH370: Expert needed to disable B777 systems

KUALA LUMPUR: If multiple communication systems aboard Flight 370 were manually disabled, as investigators increasingly suspect happened, it would have required detailed knowledge of the long-range Boeing777's inner workings.

The Wall Street Journal said 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 WSJ 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.

The shutdown of the on board reporting system shortly after the jet was last seen on radar, can be performed in a series of keystrokes on either of the cockpit's two flight management computers in the cockpit.

The computers are used to set the performance of the engines on takeoff, plan the route, as well as other functions to guide the 777.

After vanishing, the jet's satellite communications system continued to ping orbiting satellites for at least five hours.

The pings ceased at a point over the Indian Ocean, while the aircraft was at a normal cruise altitude, say two people familiar with the jet's last known position.

Investigators are trying to understand that loss, and whether or not "something catastrophic happened or someone switched off" the satellite communication system, says one of the people.

A physical disconnection of the satellite communications system would require extremely detailed knowledge of the aircraft, its internal structure and its systems.

The satellite data system is spread across the aircraft and disabling it would require physical access to key components. 

Disconnecting the satellite data system from the jet's central computer, known as AIMS, would disable its transmission. The central computer can be reached from inside the jet while it is flying, but its whereabouts would have to be known by someone deeply familiar with the 777.

Getting into the area housing the 777's computers would "not take a lot" of knowledge, said an aviation professional who has worked with the 777.

However, this person added, "to know what to do there to disable" systems would require considerable understanding of the jet's inner workings.

Some airlines outfit the access hatch to the area below the floor with a special screw to prevent unauthorized intrusion, the person added.

Orbiting satellites are designed to check in with the aircraft's satellite-communication system hourly if no data is received during that time.

The pings from the aircraft became a subject of scrutiny earlier this week, said a person familiar with the matter, several days after the plane first went missing.

Because the pings between the satellite and the aircraft registered that the aircraft's satellite communications system was healthy and able to transmit, the data did not immediately raise any red flags in the hours after the jet's disappearance.

At first, the origin of the final ping from the Malaysia Airlines jet seemed like an anomaly to investigators, according to a person familiar with the matter, given that the plane was believed to have crashed off the coast of Vietnam, hundreds if not thousands of miles from the location of the final ping.

Until just a few years ago, the satellite communication system used by jetliners didn't include data on an aircraft's location in the pings, the electronic equivalent of handshakes used to establish initial contact.

For instance, before Air France Flight 447 crashed into the Atlantic Ocean in 2009, the jet sent some diagnostic data indicating problems with various onboard systems, including the autopilot's deactivation. But notably the plane's position wasn't transmitted with that data.

Partly as a result it took nearly two years to locate the plane's "black boxes" and the majority of the wreckage. In the case of the missing Malaysian jetliner, precise locations were provided. However, it is unclear why the transmission ceased and where the plane may have ended up after the final ping.

An expert would be needed to disable the systems on the missing Malaysia Airlines jet. The headline to an earlier version of this story incorrectly said an insider would be needed.