Europe June 11, 2009, 3:12PM EST

Air Safety Experts: Improve Black Boxes

The Air France crash over the Atlantic highlights the importance of in-flight voice and data recorders. Why don't they relay their data in-flight?

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The message arrived at 2:14 a.m. GMT. It was encoded, no longer than a text message, and it was a portent of doom: 213100206ADVISORY.

Last week, engineers at Air France (AIRF.PA) decoded the transmission to mean: "drop in cabin pressure." The message of the plane's impending demise was sent by the computer system on board the Airbus A330. Then the communication system went silent. Two hundred twenty-eight people died in the crash, but by Monday—after a long search—only 17 bodies had been found in a deep part of the Atlantic.

The circumstances of the crash of flight AF 447, from Rio de Janeiro to Paris, seem almost sinister. An aircraft disappears, far from the nearest radar system, and no physical traces are found for days—except a computer-generated obituary, probably transmitted at the very moment of the catastrophe, thanks to a technology used in most modern jets called ACARS, or Aircraft Communications Addressing and Reporting System.

In their last radio message, the pilots had reported flying through black, electrically charged thunderclouds. What happened after that remained a mystery, at least until investigators last week managed to piece together a vague explanation based on the last 24 ACARS transmissions, pinged by satellite to the control center in Paris.

According to one message, 221002006AUTO FLT AP OFF, the autopilot system was switched off in the turbulence of the tropical storm. The first of the indicator panels in the cockpit failed a short time later.

Captain Marc Dubois, a highly experienced pilot with more than 11,000 flight hours under his belt, was confronted with a fatal situation. On a pitch-black night, in the midst of a thunderstorm, with no view of the horizon or any other points of reference he could have used for orientation, the instruments he needed to show him the position of the aircraft began to fail.

It is particularly difficult for a pilot, faced with such a situation, to no longer know what his air speed is. But this was precisely what one of the messages ACARS sent to the control center in Paris indicated: 341040006NAV ADR DISAGREE—an error message feared by pilots.

Several sensors mounted on the fuselage below the cockpit measure the flight speed of the aircraft based on air flow. However, these sensors reported different flight speeds, presumably because at least one of them had iced over in the storm.

Last Thursday, aircraft manufacturer Airbus explained, in an "Accident Information Telex" it sent to all airlines operating Airbus models, how pilots faced with such a situation can determine their correct speed. Last Friday evening, Air France announced plans to accelerate the replacement of air-speed sensors on its Airbus planes.

But how did the 58-year-old captain and his two copilots react?

Missing Pieces

If search teams fail to recover the flight recorder, which consists of two metal devices that record flight data and cockpit conversations, this question may never be answered. "It would be a real shame for aviation," says Robert Francis, the former vice chairman of the National Transportation Safety Board, the agency that investigates aviation accidents in the United States. "If we want to avoid dramas like this in the future, we have to know what went wrong," says the safety expert. For this reason, Francis wants to see all important flight data transmitted via satellite in the future, using ACARS technology. "This crash demonstrates how valuable this technology could be," he says.

Significant upgrades to aircraft would not even be required, according to Francis. All that is needed, he says, is to reprogram the software in the communication system, turning it into a sort of online black box. Krishna Kavi, an engineer and professor at the University of North Texas in Denton, presented the US Federal Aviation Administration (FAA) with a similar system 10 years ago. "The cost is low," he says.