Andrew Doyle/MUNICH Julian Moxon/PARIS Max Kingsley-Jones/LONDON
French investigators are trying to establish whether the 25 July crash of Air France Aerospatiale/British Aerospace Concorde F-BTSC can be linked to previous incidents in which tyre bursts have resulted in punctured fuel tanks on the supersonic airliner.
Having taken off from Paris Charles de Gaulle airport, the aircraft went down after fuel pouring from a ruptured tank caught fire. Air France's Concorde fleet remains grounded but British Airways resumed its normal flight schedules soon after the crash.
The French accident investigation bureau (BEA) says part of the toughened fibre glass water deflector from the left main landing gear was among debris found on the runway following the accident.
The crash follows a string of potentially disastrous Concorde tyre-related incidents.
A UK Air Accidents Investigation Branch (AAIB) probe into an October 1993 tyre burst incident involving a taxiing BA Concorde, in which a fuel tank was penetrated, found that debris from a broken deflector was "almost certainly" responsible for the airframe damage. Air France, unlike BA, did not carry out subsequently recommended modifications to the deflectors on its aircraft.
BEA chief Paul-Louis Arslanian confirms the deflector issue forms "one of the elements of the inquiry" into the Air France crash. A water deflector, or "cow-catcher", is mounted at the front of each of the two main landing gear bogies (see diagram). Weighing nearly 5kg (11lb), it is designed to prevent surface water being ingested by the adjacent engine intakes.
Concordes have suffered a catalogue of tyre bursts since the type entered service in 1976. These include at least nine incidents which resulted in significant damage to the airframe and/or engines between 1979 and 1993 (see table). A broken water deflector was specifically implicated only in the 1993 incident, while in the other cases the damage was found to have been caused by flying tyre debris and/or wheel shrapnel.
The BEA has revealed that the inboard front tyre on the left main landing gear was destroyed during the take-off run, a piece of servovalve body and a piece of fuel tank structure were also recovered from the runway. The debris, which did not include any engine or wheel rim parts, was collected beyond the point at which decision speed (V1) would have been reached, says the BEA. A piece of the tyre found on the runway contained a large rip. A 40cm-long metal object, unrelated to Concorde, was also found on the runway.
The AAIB report into the October 1993 BA tyre burst incident at London Heathrow airport, published in mid-1994, says the UK carrier had "asked the manufacturer to review the design of the water deflector, which it and the AAIB consider responsible for penetration of the fuel tank, despite assurances from the manufacturers that it was one of the design objectives of this component that it should not be capable of doing so."
On 12 January, 1995, Aerospatiale, now part of EADS, issued a service bulletin (SB) recommending the insertion of a steel cable into the toughened fibre glass to prevent the break-up of the water deflector in the event of a tyre burst. The SB was not mandated as an airworthiness directive by the UK and French authorities.
BA confirms that it modified its seven-strong fleet of Concordes in accordance with the SB, completing the work in September 1995. "The modification means that any debris from the water deflector could not come away in the event of a tyre burst," claims the UK airline.
Air France says: "This modification consisted of reinforcing the deflector, but not in such a way as to prevent it from separating from the landing gear in the event of an impact. It was designed simply to ensure that the deflector would remain in one piece, should it come loose from the landing gear after an impact."
Air France suffered several serious tyre burst incidents at US airports between June 1979 and February 1981, which attracted the attention of the US National Transportation Safety Board (NTSB). It wrote to the French BEA in November 1981, expressing concerns over "four potentially catastrophic incidents resulting from blown tyres during take-off" from Washington Dulles and New York JFK airports.
The most serious of these occurred on 14 June 1979, when two tyres on the left main gear of an Air France Concorde burst on take-off from Dulles. Tyre debris and wheel shrapnel damaged the No2 engine, punctured three fuel tanks and severed hydraulic lines and electrical wires. In addition a large hole was blown through the top of the wing skin above the wheel well. A similar incident occurred six weeks later, prompting the French DGAC to issue an airworthiness directive requiring the inspection of each wheel and tyre for "condition, pressure and temperature prior to each take-off".
A "flat tyre detection system" was installed on the Concorde fleet in the early 1980s to alert pilots to tyre failures that occurred in the take-off run between 10 and 135kt (18.5 to 250km/h). The system, however, was not included on the minimum equipment list (MEL) and so was not required to be serviceable prior to departure. If the system was not serviceable, tyre pressure checks were required prior to departure. Since the 25 July accident BA has included the system on the MEL. It is not known whether the system was operable on the Concorde at the time of the crash.
Concorde is particularly vulnerable to damage from tyre bursts because of its unusually high take-off and landing speeds, and the fact that the wing skin above the landing gear is much thinner than on subsonic airliners. It also has a higher rate of rejected take-offs.
Air France pilot union president Michel Le Bras, says: "The crash revealed the vulnerability of Concorde in the area of tyres. It is necessary to put in place stringent measures to minimise tyre risks."
The French Government is unlikely to lift its flight ban on French Concordes until investigators have completed their preliminary report at the end of this month. "There are still uncertainties over the interpretation of the chain of events leading to the accident, and it is therefore not possible to answer the questions which seem central towards establishing the necessary conditions for a return to flight," says the French transport ministry.
Though this is the first fatal accident suffered by the Concorde fleet in its 24 year service history, it has completed fewer flight cycles (76,000) than are accumulated by the worldwide Boeing 737 fleet each week. BA, which operates the lead aircraft, is approaching a decision on whether to go ahead with a major life extension programme which is required to keep its Concordes flying beyond 2005.
British Airways says that there has been no detectable fall in bookings as result of the accident, and Concorde charter specialist Goodwood Travel holds a similar view. "We've had some cancellations but these have been more than replaced by wait-listed passengers or new bookings," it says.
BEA FINDINGSStatement 1 - 27 July During take-off, as the aircraft passed V1, the control tower signalled to the crew that there were flames at the back of the aircraft. The crew announced immediately after take-off that the No2 engine had failed and that the landing gear would not retract. The flight data recorder showed that during rotation, No2 engine wound down and stopped while No1 experienced a temporary power reduction. The speed and altitude of the aircraft hardly changed after take-off. The aircraft was airborne for under a minute, during which No1 engine lost power completely. The aircraft banked left and crashed. Statement 2 - 28 July Examination of material found on the runway showed that most of it came from the left side of the aircraft. It also showed the destruction of one, and possibly two tyres on the left main landing gear. No internal engine debris was identified. The origin of the fire was "external to the engines and remains to be determined". Statement 3 - 30 July Aircraft weight at take-off was 185.1t of which 95t was fuel. The announcement of "V1" by the crew took place 32 seconds after brake release, with the aircraft having travelled 1,200m (3,900ft). All debris was found beyond this point. One piece of debris appeared to come from a fuel tank. The aircraft reached rotation speed 900m after V1. The flames seen after take-off did not come from an engine but in all likelihood from a major fuel leak. Statement 4 - 1 August There were no problems with the aircraft prior to departure. None of the debris identified on the runway came from an engine.
Source: Flight International