Concorde supersonic jets had at least a dozen blown tire incidents before the crash of an Air France Concorde earlier this week, according to safety reports obtained by ABCNEWS.com from U.S. aviation agencies and accounts by British Airways.
In light of the fatal crash, those incidents raise questions about the design of the world’s only supersonic commercial jet, experts say.
Evidence released Friday by French authorities suggests a tire blowout during takeoff of the Air France Concorde at Paris’ Charles de Gaulle airport initiated a sequence of events that led to the crash Tuesday, killing all 109 people aboard, and four more on the ground.
Debris from a blown tire can rupture fuel tanks and fuel lines and be sucked into engines, which are uniquely located above the open landing gear on a Concorde.
French authorities said Friday they believe one tire and possibly two burst as the Concorde was accelerating down the runway.
In examining the evidence so far, investigators also have determined that the No. 2 engine, located near the tire blowout, failed early in the flight. And as a fire raged from the wing in the vicinity of No. 2, a second engine housed next to No. 2 also failed just before the plane crashed into a hotel.
But investigators have not yet announced a conclusion on what was ultimately responsible for the crash. In addition to looking at tire debris as a possible cause, they are probing the possibility that improper engine maintenance or a faulty part could have brought down the plane. Following this weeks’ crash, Air France grounded its fleet of Concordes, but British Airways Concordes continue to fly.
Since entering service with British Airways and Air France in 1976, the Concorde has been revered as one of the safest jets in service. Until this week it was never involved in a fatal accident.
But a ruptured tire on a Concorde can be especially serious, experts say, because of the aircraft’s unique design, which allows it to cruise at twice the speed of sound.
Unlike in most commercial jets, the Concorde’s rear tires are located directly below the wing fuel tanks, and in close proximity to the engines.
“One of the biggest problems here is the location of the wheel assembly, vs. the engine and engine intakes,” says ABCNEWS aviation analyst John Nance. “They couldn’t be more catastrophically co-located.”
He notes that two of the four tires under each wing of the aircraft are positioned just forward of the area where the engines suck in air.
“What’s going to happen if you peel a tire or blow a tire, is debris is going to go up and go right through that vacuum,” says Nance.
Chris Yates, of the aviation magazine Jane’s, says if a tire did blow on the Concorde, it might well have ruptured a fuel line and/or fuel tank, causing the number No. 2 engine to starve for fuel.
And he adds: “If those two tires did go, as the French seem to be suggesting … and with fuel spilling, bearing in mind the engines were in theory on afterburner, that would cause that huge flame.”
Afterburners provide additional thrust for Concorde on takeoff and during supersonic flight by adding a combustable fuel-air mixture to the exhaust at the back of the engine.
Previous Tire Problems
In fact, early in the service life of the aircraft, Concorde jets suffered a series of tire blowouts, including at least two in 1979, one in 1980 and one in 1981 at airports in the United States. (See related stories, above right, for aviation agency documents.)
The most serious incident occurred at Washington’s Dulles International Airport in June 1979, when two tires blew out on the left landing gear. Debris punctured three fuel tanks, severed hydraulic lines and electrical wires, and damaged the No. 2 engine. Fuel poured out of the wing, but didn’t catch fire.
The Concorde’s design, with its long fuselage, puts a particularly large amount of stress on the tires, especially as the nose rotates up during takeoff, says Mike Dornheim of Aviation Week & Space Technology magazine.
Concorde tires are usually changed after about 35 flights, according to British Airways officials, while a typical jet might have its tires changed after anywhere from 92 to 300 flights, depending on the jet and a number of other factors.
“It’s an airplane that would tend to have a lot of stress on the tires, particularly at rotation,” says Dornheim. “You couldn’t think of a worse airplane for tires.”
But he adds the designers of the Concorde probably designed special tires to handle the load.
How Well Fixed?
A number of corrective actions were taken in the early ’80s by the Concorde operators to deal with the blowouts, including increased tire inspections and monitoring, and new procedures for pilots to deal with the problem.
Additionally, the plane’s operators decided to stop using re-treaded tires on the aircraft and installed sensors to let the crew know if a tire has blown, or if its pressure is not balanced.
But it’s not clear how successful the fix was at preventing tire blows over the years.
The U.S. Federal Aviation Administration says it has no data indicating additional Concorde blowouts in the United States since 1981.
The FAA data is incomplete, though, since the agency has been unable to locate incident reports for the Concorde from between 1988 and October 1996, according to spokesman Les Dorr.
British Airways, though, reports 12 tire failures on its Concordes since 1988.
But none of those, of course, resulted in a catastrophe.
In fact, one British Airways captain recounts how a Concorde safely flew across the Atlantic after a piece of tire had torn off and was ingested by an engine, damaging the turbine. The engine continued operating and the pilot was not aware of the damage until after landing.
After reaching a certain speed, Concorde’s are built to fly with two engines on one side of the plane disabled.
“Probably a lot of tire bursts never make it into the papers,” says Dornheim.
A Record of Safety
Jane’s Yates says even if French authorities do determine with certainty that a tire did ultimately cause the crash, it shouldn’t necessarily mean the aircraft in operation are unsafe and should be grounded until changes are made.
“There hasn’t been an instance of a major tire blowout for some considerable time now,” he says. “It’s highly likely that the problems that were experienced in the late 1970s and early 1980s were addressed, and addressed effectively.”
But Nance questions whether the plane is built to safely withstand the damage caused by a severe blowout, if it does occur.
“Quite frankly, you can probably build tires that are even tougher. Maybe you can build the wheels to take 350 to 400 knots, instead of just 250 to 300, or whatever they’re rated for,” says Nance.
“But other than putting metal plates of some sort all along the tanks on the underside and changing the aerodynamics and the weight of the airplane, I don’t know how in the heck you could insulate against puncturing wing tanks, which is where the fire came from,” he says.
“And I certainly don’t know how you can insulate the engines, which is where it appears the crash came from,” he says.