With reliable electronics, transponders should always be on

Malaysian officials are issuing ambiguous statements about the timeline surrounding loss of voice, civil-radar, and data-communications contact with the missing MH370. But if Gregg Easterbrook had his way there would be at least one fewer source of potential ambiguity. Hijackers or rogue pilots, he writes in the New York Times, should not be able to turn the units off.

In the Times, Easterbrook writes, “When mass murderers took over the cockpits of four American airliners on Sept. 11, 2001, one of the first things they did was turn off the transponders, so the planes would not register properly on civilian radar.”

Easterbrook wrote a chapter on aviation security for the Council on Foreign Relations' book on mistakes leading to the 9/11 tragedy, titled How Did This Happen? In his Times article yesterday, he says, “At the time, I would have bet my life’s savings that the transponder, which broadcasts an aircraft’s location and identity, would be re-engineered to prevent hijackers from turning such units off. But nothing was done. Almost 13 years later, Malaysia Airlines Flight 370 sparked a lengthy worldwide search when, it appears, another transponder was turned off.”

The ability to turn the transponder off from within the cockpit, he says, is a throwback to an earlier era before reliable chip-based electronics and radar that could be confused by transponders operating on taxiways.

Many experts, including ones that commented on Easterbrook's Times article, contend that it is necessary for pilots to be able to disconnect any electrical device in the event of a malfunction—whether due to a short-circuit or inaccurate transmission. One commented that it's impossible to make a plane pilot-proof. At the very least, however, if a transponder must be disabled in flight, the process should automatically start up a backup unit.

Commenter VJR, who self-identifies as an avionics systems engineer, offers the interesting proposal that four GPS transceivers—located at each wingtip and at the nose and tail—should operate independently. A significant change in relative position would indicate structural disintegration.

And finally, it's worth noting that the collision of Gol Transportes Aéreos Flight 1907 and an Embraer Legacy business jet over Brazil in 2006 was attributed in part to the Embraer's transponder being inadvertently turned off.

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