Do Computers Make Planes Less or More Safe?

August 3, 2009 — -- Ben Cave was starting to get bored. The Australian had been sitting in his seat for more than three hours, and he still had two hours left before the Qantas jet was scheduled to touch down in Perth.

The Airbus A330 was flying at a cruising altitude of 11,278 meters (37,000 feet). The calm of modern jet travel, accentuated by the monotonous drone of the engines, prevailed on board the aircraft. The flight attendants were clearing away the last of the lunch trays into their trolleys, some of the 303 passengers were waiting near the toilets, and others were passing the time with stretching exercises.

Ben Cave unfastened his seatbelt, stood up, opened the overhead luggage compartment and fished around for a magazine and a pen, hoping to make the remainder of the flight pass more quickly.

That was when the longest few minutes of his life began.

At 12:40 p.m. and 28 seconds, the autopilot in the cockpit suddenly disabled itself. While the unsuspecting Cave was digging around in the overhead luggage compartment, lights were flashing and alarms were going off in the cockpit. Error codes flashed onto the central monitor: AUTO FLT AP OFF, NAV IR1 FAULT. Then a metallic voice said, ominously: Stall! Stall! Stall! Danger: The aircraft is too slow. The airstream over the wings is about to decrease!

Then there was another warning sound and the words, in red, appeared on the screen: Overspeed! Overspeed! Overspeed! The aircraft is too fast!

For a few seconds, the captain and the co-pilot must have thought that they were merely dealing with the quirks of a flight computer. The engines were running normally, the aircraft was perfectly positioned in the airstream and the weather radar was not reporting any turbulence.

"What's this thing doing now?" the irritated pilot usually says at such moments, and in most cases all it takes to fix the problem is to restart the computer, or simply wait until the computer resets itself.

But this time it seemed as if an invisible hand had taken control of the aircraft. A few moments later, at 12:42 and 27 seconds, it became clear that it was not going to be business as usual on board Flight QF 72. The nose of the aircraft was suddenly pitched sharply downward, 8.4 degrees over the horizon, headed toward the earth. The aircraft quickly picked up speed and the sound of air rushing by grew louder. The plane was in a nosedive.

"My head hit the cabin ceiling," says Cave, remembering his experience on that Oct. 7, 2008, en route from Singapore to Perth. All around him, passengers were suddenly flying into the air, their bodies smashing against the plastic ceiling, where they remained frozen in place. The forces that had suddenly been unleashed seemed capable of controlling the passengers' bodies like puppets on a string.

"For a few seconds, I thought it was all over," says Cave.

As in the cabin, there was a feeling of powerlessness, of being in the hands of fate, in the cockpit of the A330 with the tail number VH-QPA. Using all of his strength, the pilot pulled back the control stick, desperately trying to get the plane back onto a safe horizontal flight path. But for several long seconds, his efforts were completely ineffective.

As if guided by evil forces, the Airbus was plunging to its doom.

Just as unexpectedly as it had taken control of the aircraft, the computer relinquished that control and the nose of the A330 suddenly returned to normal. The passengers were thrown back into their seats or onto the floor at one-and-a-half times the force of gravity.

"There was utter chaos around me," says Cave. Only three minutes later, the plane went into another eerie, uncontrollable nosedive. At 12:49 p.m., the aircraft transmitted an emergency "Mayday" message, followed by a second one five minutes later.

"The pilots are real heroes," Cave said ecstatically after an emergency landing at a tiny military base on the west coast of Australia.

But if the pilots are heroes, they are tragic heroes at best.

Instead of being able to pilot the plane, they were briefly transformed into helpless spectators. And it wouldn't have been long before they too became the victims of a plane gone amok, no longer stoppable by human intervention. If the nosedive had lasted a little longer, the plane might have reached a speed at which the pilots could no longer stop it without it breaking apart. The difference between life and death was a matter of seconds.

The incident on board Flight QF 72 resulted in 115 injuries, 12 of them serious, as well as two spinal injuries. The cabin ceiling was severely damaged in many places. "The oxygen mask was hanging down from the spot where I hit the ceiling," says Cave.

His wounds have long since healed, but the incident has left its mark on the pilots. There are 621 A330s in operation today, and one of them suddenly embarked on a bizarre life of its own.

What exactly happened on the circuit boards of aircraft computer system remains unclear. Defective readings apparently confused the flight computers, leading them to believe that the passenger jet was climbing steeply instead of cruising along a stable, horizontal path. This prompted the computers to push the nose down, without any pilot input, to protect the aircraft from the perceived danger of sideslipping. "We want to know, as quickly as possible, how exactly this could have happened," says a Lufthansa pilot who flies the same Airbus long-haul aircraft.

Julian Walsh, of the Australian Transport Safety Bureau (ATSB), openly articulates what the manufacturer and the airline would prefer to keep quiet about Qantas Flight 72: "Certainly there was a period of time where the aircraft performed on its own accord."

This arouses our primal fear of technology acting independently and assuming power. Just as HAL, the on-board computer in Stanley Kubrick's sci-fi classic "2001: A Space Odyssey," assumes control of the spaceship, the Qantas computers made arbitrary decisions.

The crash of another Airbus A330 on June 1, 2009, raises similar concerns. Air France flight AF 447 was at cruising altitude en route from Rio de Janeiro to Paris when it suddenly plunged into the Atlantic Ocean and killed all 228 people on board. It is possible that the real cause of the crash will never be known.

In that accident, the final signals that were transmitted by the doomed aircraft's computers via satellite also provide evidence of digital problems on board. Twenty-four matter-of-fact maintenance messages to headquarters in Paris indicate that the speed sensors reported defective data, and that the flight computers switched themselves off because they were incapable of processing the contradictory data.

What happened in that stormy night over the Atlantic? Were the pilots overwhelmed by crashing computer systems? Did the jumbled error messages cause them to make a fatal mistake? "Whatever the eventual findings, the crash already is prompting questions about how thoroughly aviators are trained to cope with widespread computer glitches midflight," writes the Wall Street Journal.

The British trade publication Flight International also anticipates a new debate over air safety and cites, in particular, the February crash of a Turkish Airlines Boeing in Amsterdam. During the landing approach, a malfunctioning altitude indicator reported that the plane was already two meters below the runway. The computer that controls the automatic thrust control system, believing that the aircraft was already on the ground, reduced engine power. The pilots ignored the change, perhaps because they had placed too much trust in the computer.

The Boeing 737 eventually crashed into a field near the runway, killing nine on board. "The issue of the human factors associated with operating highly automated aircraft is likely to move up the agenda once more," Flight International predicts.

That agenda will probably be influenced by the final report on the near crash of a Lufthansa flight due out this autumn. In March 2008, the wing tip of an Airbus A320 scraped across the runway at Hamburg Airport in strong crosswinds. The dramatic images of the near crash quickly circled the world in the form of an amateur video that was eventually viewed millions of times on the Internet.

The pilots were initially described as heroes for having saved the plane. But then the tabloids sharply criticized the co-pilot for being inexperienced and inept.

"But now the situation turns out to be more complex," says Johann Reuss, the investigator with the German Federal Bureau of Aircraft Accidents Investigation (BFU) who was assigned to the case. He cannot comment further, because the final report has not been released yet.