Accident Analysis - The End

Till date, the cost of supersonic air travel remains formidable and there are no prospects of an early resumption of commercial supersonic flights

On July 25, 2000, Air France Concorde Flight 4590 met with a fiery end, a couple of minutes after take-off from Paris. In a dramatic sequence of events, reminiscent of the proverbial rhyme ‘for want of a nail’, the swiftest chariot in the skies was reduced to a blazing wreck ostensibly due to a foreign object on the runway. Only this time it was not ‘for want of…’ but because of a lethal piece of metal just three centimetres wide and 43 centimetres long, lying unnoticed in the path of the take-off roll of the airliner. All 100 passengers and nine crew onboard the flight plus four on the ground, perished. The accident, Aérospatiale-BAC Concorde’s only major mishap, marked the beginning of the end of the world’s only successful supersonic airliner.

Flight 4590, with Captain Christian Marty in command, commenced its take-off roll from runway 26 (R) of Paris’s Charles de Gaulle International Airport at 16:42:31 (local time), bound for John F. Kennedy International Airport, New York City. At 16:42:55, the co-pilot called 100 knots, then V1 speed (150 knots) after nine seconds. A few seconds later, the front right tyre of the left landing gear apparently sustained damage. A large chunk of tyre probably broke off and struck the underside of the aircraft’s wing structure near fuel tank No 5, just above the left main landing gear, severing some electrical cables. A pressure shockwave developed that eventually ruptured the fuel tank at its weakest point. Fuel gushed out over the top of the wing at a rate of some 130 gallons per second. Electrical arcing of the damaged 115 V circuit (which provided power to the brake system cooling fans) ignited the volatile fuel-air mixture. A huge fire, fed by the torrent of leaking fuel, broke out at the trailing edge of the left wing. Around the same time engines No 1 and 2 suffered loss of thrust—severe for engine No 2, slight for engine No 1. The Air Traffic Controller in the tower advised the crew that their aircraft was trailing fire. Since they had crossed V1, the crew continued with the take-off. At around 16:43:22, the engine fire alarm sounded and shortly thereafter the flight engineer announced that he had shut down engine No 2. Then the captain called for emergency procedure for engine fire. A few seconds later, the fire handle of engine No 2 was operated and the fire alarm stopped. The co-pilot drew the captain’s attention to the airspeed, which was just 200 knots.

At 16:43:30, the captain called for landing gear retraction. The controller on the ground again reported the presence of large flames behind the aircraft. The engine fire alarm sounded a second time for around 12 seconds. At 16:43:56, the co-pilot commented that the landing gear had not retracted and made several callouts in relation to the low airspeed. The engine fire alarm sounded a third time at about 16:43:58 and stayed on until the end of the flight. In all, the aircraft flew for around a minute at a speed of approximately 200 knots and at a radio altitude of about 200 feet, but was unable to gain any more height or speed. The fire caused severe damage to the left wing and it began to disintegrate. Engine No 1 surged a couple of times, then failed. Due to the asymmetric thrust, the aircraft rolled to the left by 100 degrees. The crew reduced power on engines No 3 and 4 (on the right) in a vain attempt to level the wings of the aircraft. However, with the falling airspeed, they lost control and the aircraft entered into a steep violent descent rolling to the left and plummeted into the Hotelissimo Hotel as it burst into flames.

The final accident report by France’s official investigation agency, the Bureau Enquêtes-Accidents (BEA ) was published on December 14, 2004. It observed that four minutes before Flight 4590 commenced its take-off run, a McDonnell Douglas DC-10 airliner belonging to the USA-based Continental Airlines had lost a titanium strip, part of a thrust reverser, during its take-off run. This small strip of metal lying on the runway probably punctured the Concorde tyre, which subsequently disintegrated. A 4.5 kg piece of rubber from the tyre hit the fuel tank and set off the chain of events that culminated in the disaster.

BEA observed that the Concorde was airworthy and the crew were qualified. The report said that the landing gear which failed to retract when selected, had not revealed any serious problem in the past. Its failure was presumably caused by damage from tyre fragments. What if the crew had decided to abort take-off, contrary to laid down procedure? The report opined that there would have been a high-speed runway excursion and collapse of the landing gear which would have ended in an equally devastating crash.

Since a burst tyre probably led to the loss of the aircraft, the BEA went into the entire history of Concorde tyre failures. In all, investigators documented 57 cases of tyre bursts/deflations. Astonishingly, Concorde had one recorded instance of tyre deflation/destruction per 3,000 flights over the five years immediately preceding the accident. In comparison, for the subsonic Airbus A340, the rate is of the order of just one per every 1,00,000 flights. In one experiment, actual pieces of tyre were fired at a dummy Concorde fuel tank. A piece weighing some 4.5 kg travelling at a speed of 140 m/s succeeded in rupturing the tank. And a Concorde tyre burst at take-off speed could easily hurl a similar-sized chunk at this speed at the lower wing surface. Concorde seems to have had a string of narrow escapes before its luck finally ran out.

According to some aviation experts, the BEA seemed rather eager to pin the blame on the DC-10’s titanium strip (a component that, incidentally, had not been approved by the US Federal Aviation Administration) thus absolving Air France and Aérospatiale-BAC of responsibility. This was not the first foreign object on a runway nor will it be the last. But is it acceptable for an airliner to be so vulnerable to damage?