Concorde at Heathrow
Considering the nature of Concorde’s design and the operations it undertook, Concorde was remarkably reliable and trouble free during its service life, any problems which has arisen have been reasonably easy to fix.
One of the more visible problems was the failure of the upper rudder on some of the aircraft. The first failure (resulting from delamination) occurred in April 1989 when BA’S G-BOAF (216) lost part of its rudder while flying between Auckland and Sydney at supersonic speed. The aircraft was in the middle of a 38,300 miles (61,600km) circumnavigation of the world charter when the incident took place and the aircraft was landed safely at Sydney. After repairs, it was able to continue the flight.
Concorde G-BOAF, showing the damage to the upper rudder
A second upper failure occurred in January 1991, prompting development of an improved design which would eliminate the problem. Nine replacement rudders sets were built at a cost of £5 million, the first of them fitted in 1993.
In 1994, hairline cracks were found in the aft wing spar webbing of all British Airways Concorde’s. Two airframes were immediately repaired and the remainder cleared to continue flying subject to an inspection every 10 flights. The affected part was not load bearing and the repair was simple.
An inspection of Air France’s Concorde’s revealed no sign of the cracking, which was not unexpected as its aircraft have lower hours logged than BA’s, annual utilisation of the aircraft averaging only about two-thirds of that recorded by British counterparts.
One problem of a non structural nature which had to be overcome was that of fitting traffic alert and collision avoidance systems (TCAS) which are now mandatory for operations in the USA.
TCAS Indicator
Concorde problems with tyre-burst on take-off’s
Concorde’s closest call occurred at Washington in 1981 to an Air France aircraft which suffered a double tyre-burst on take-off. Debris knocked out two engines and punctured the wing fuel tanks, causing fuel to pour on to hot brakes. This incident, very nearly a serious accident, led to a unique modification—a soft-tyre sensor on the main undercarriage bogie beams. These twist when a tyre softens, causing a warning light to illuminate on the pilots’ panel up to 135kt. This modification has given many soft-tyre warnings—12 in BA’s fleet, all during taxiing, and all caused by foreign objects on the runway.
Concorde’s Dunlop tyres were thin high-pressure (2201b/in ) three-beaded 32- crossply structures with the industry’s highest loadings and take-off speeds (typical VR=200kt). They were inevitably vulnerable to foreign-object damage. After the Washington incident, Concorde’s tyres were up rated and the wheels strengthened to provide roll-on-rim capability. At the same time, to avoid repetition of the companion-tyre failure which had happened at Washington, protective plates were fitted. Since then there were no more contagious tyre failures, though enough single ones, until the Paris crash. In a well publicised incident at Heathrow, when a BA Concorde captain ordered an evacuation, a small flash fire followed a tyre burst and punctured fuel tanks on take-off. Within 24hr the same operator had another Concorde evacuation, following an electrical problem which affected the anti-skid system and thrust reversers. Though the incident was not really chargeable to the undercarriage, another brake fire alert caused the second of only two emergency slide evacuations since Concorde entered service—to one operator within 24hr and for unrelated reasons. Although British Airways engineering opinion favoured retreads, which can be better than new tyres, the British operator did not fit them to Concorde “for PR reasons” according to one engineer. Air France allowed two or three retreads. A new tyre lasted 40 landings, compared with a 737’s 200. The Dunlop carbon brakes have pioneered this material’s superior performance as a stopper of aircraft, especially in the rejected-take-off case. Boeing and Airbus decided to go for carbons on the new twins as a result of good Concorde experience. The brake units themselves are very reliable, and certainly stop the aircraft. Bogie-twisting has caused some pad breakages, the brake pedal transmitter has been unreliable, and a gentle touch is required when taxiing to avoid “snatch” and broken pads. But Concorde’s carbon brakes have been “good news”, to quote a BA engineer, pioneering all of tomorrow’s subsonic brakes.
Hose jobs
Aerospatiale were asked to modify the brake hoses, which have suffered fractures. They are under the trucks, and protection or rerouteing was desirable.
Droop nose
Like the undercarriage, Concorde’s unique “snoot” has never failed to lower for landing. The pilots were trained to handle such an awkward eventuality, and they had complete confidence in the GEC/Sfena Cat 3 autoland—which one BA engineer regarded as the Concorde’s most successful example of Anglo-French engineering co-operation— the British doing the pitch and the French the lateral control boxes.
Structure
One of the biggest airworthiness worries in Concorde’s early project stage was the structure, which would have to withstand the fatigue of supersonic heating as well as the loads of higher cruising altitudes and speeds. In the event Concorde has had few structural problems. The seven BA aircraft each flew about lOOhr a month, and Air France’s four about 50hr. Hot-testing of the full-scale structural specimen which took place Royal Aircraft Establishment Farnborough had been completed after the equivalent of 20,000 supersonic cycles (say 60,000hr at 3hr per flight). Erudite discussion by structures experts seemed to agree on a safety factor of three, giving Concorde a service life of between 6,500 and 7,000 supersonic cycles. This would mean that the first British Concorde’s would have to be retired, at present rates of use, around 1996, but of course with re-life work they flew until 2003. The French expected their high-time aircraft to reach 6,000 cycles in the year 2000. Time would tell if a safety factor of three is over-cautious. This would have to be supported by careful monitoring and inspection of actual service aircraft, the best test specimens of all. How this will be done (and financed) was at the time still open for debate, but the signs were pointing towards a major structural audit at, say, 4,000 cycles. This would concentrate on the most “structurally significant” areas, as indicated by the Farnborough specimen, which was being cut into 40 critical components for further testing in BAe and Aerospatiale laboratories.