There’s still no clear answer as to what caused Air France Flight 447 to crash in the Atlantic Ocean in June. But there are lots of theories. Britain's Daily Mail this week cited wiring expert Edward B. Block on the possibility that faulty wiring and wiring insulation could have been the cause of the crash.

Speculation on Flight 447 aside, there may be a larger potential problem: the Federal Aviation Administration does not require tests to determine when and under what conditions electrical wiring and its insulation will fail and possibly start fires. And this is despite the role of faulty wiring insulation in several other airplane crashes.

Specifically, the insulation that surrounds electrical wire can crack over time and an electric current can arc from one crack to another. A particularly explosive effect called ‘arc-tracking’ can occur when the insulation itself chemically reacts to the current and potentially starts a fire. One insulation type, Kapton, is especially prone to arc-tracking, and according to a January 2008 study commissioned by the FAA, “should not be used in airborne applications.” But it is still used in thousands of older planes.

“Why are there tests for the safety of every part of the aircraft except the part that starts the fires?” Block, a former FAA consultant and former Defense Department employee, asked PaperTrail.

It’s not, it appears, because of a lack of awareness of the potential problem. The 1998 crash of Swissair Flight 111 off the coast of Nova Scotia was “most likely” caused by sparks from electrical wiring that caught material on fire above the cockpit, spreading fire throughout the aircraft’s electrical system, according to Canada’s version of the National Transportation Safety Board. Following that accident investigation, Canada’s board recommended in 2001 that “a certification test regime be mandated that evaluates aircraft electrical wire failure characteristics under realistic operating conditions and against specified performance criteria, with the goal of mitigating the risk of ignition.”

The Board said the FAA initially concurred with its recommendation, but still has not required the more robust and comprehensive tests.

The FAA told PaperTrail it “requires insulation on electrical wires and cables” that provide additional protection and that self-extinguish. The agency uses a test from 1972 “to demonstrate compliance to this requirement. But this test, according to Canada’s board, exposes wiring insulation surrounding an unpowered electrical wire to a flame, which does not reflect the kind of realistic conditions wiring insulation needs to be tested under.

Also, in response to a federal advisory committee on aging aircraft, “the FAA issued a comprehensive set of enhanced airplane wiring safety regulations” in October 2007, FAA spokesman Les Dorr said. These regulations “are aligned as closely as possible with the requirements for fuel tank system safety,” Dorr said.

Canada’s Board said these changes “will reduce but not substantially reduce or eliminate the” risk caused by the lack of required testing.