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CONCORDE MAKES COMEBACK

At the beginning of September Air France had completed several supersonic test flights of its own with its modified Concorde (registration F-BVFB) "Fox Bravo", and everyone was expecting the officials to give the all-clear in the near future. Suddenly everything went tense again as the French civil aviation authority apparently put its foot down on the brake and demanded some additional detailed documentation regarding the modifications that have been carried out to the Anglo-French prestige aircraft.

"We have to be absolutely clear here", explained Gérard Le Houx, spokesman for the French civil aviation authority, the Direction Générale de l'Aviation Civile (DGAC), in an exclusive interview with FLUG REVUE. "When you consider that the manufacturer formally submitted an approximately two-metre high pile of documents, 105 chapters in all, on 21 August, issuing the Certificate of Airworthiness on 5 September was quite a feat," he added.

"We did have a few queries, but that is quite normal," explains Le Houx. "The most important thing is our conclusions: working closely with our British colleagues we have satisfied ourselves that the modifications achieve the required safety standard in all the expected situations. The associated test results have been documented clearly and in detail and have been submitted to our experts."

Le Houx is not expecting any further surprises from the official final report on the Paris crash, which has still not been published. "We already had all the facts that will appear in the final report. All this data has been examined and confirmed. Even if the official final report itself is not published, say, for another two months, which is entirely the decision of the accident investigation agency, the BEA, we have had full access to all the results of its investigation."

The technical modifications required to Concorde have been made the subject of a mandatory Airworthiness Directive, compliance with which is a condition of re-certification. This means that only modified aircraft will be allowed to carry passengers in the future.

Under the terms of the joint official statement issued by the UK Civil Aviation Authority and the French DGAC, the following modifications are officially mandated:

• Installation of additional Kevlar tank linings to the bottom of the internal fuel tanks to reduce any escape of fuel in the event of damage to the tanks.
• Removal of certain electrical "ignition sources" so as to reduce the danger of fire.
• Use of new Michelin Near Zero Growth (NZG) tyres on all eight main wheels of the undercarriage.
• Mechanical strengthening of electrical wiring in the undercarriage bays in order to exclude the possibility of any sparks being generated there.
• Modification of the water deflector on the main undercarriage to accommodate the new tyre.
• Re-programming of the software for the anti-skid system to take into account the change of tyre.
• The flat tyre detection and warning system must be working on departure.
• The electrical power to the brake cooling fans must be switched off prior to take off or landing.

On 5 September the authorities were finally persuaded that the safety of the Anglo-French wonderbird had been restored, and the first Certificate of Airworthiness was returned. The only civilian supersonic aircraft in the world is thus able to resume active scheduled services.

On 25 July 2000, 130 lives were lost as a fully loaded Concorde, F-BTSC, sustained serious damage to its tanks following a burst tyre and crashed in flames onto a hotel near Gonesse, Paris with one engine shut down and one malfunctioning. All Concordes were immediately grounded, and for many months the future of the elegant prestige aircraft had appeared more than doubtful.

The CAA's argument for banning all further Concorde flights in August 2000, to which the DGAC immediately concurred, was that a single routine problem like a burst tyre must never be allowed to lead, as it did in Paris, to a fatal chain of events resulting in the total loss of the aircraft.

As the legal successor to the former joint Concorde manufacturers, Aérospatiale and British Aircraft Corporation, Airbus responded by drawing up proposals for structural design modifications to the supersonic jet, trying them out and then successfully demonstrating them to the authorities. All this had taken a year.

As well as wind tunnel and laboratory tests, extensive ground testing and flights, both subsonic and supersonic, were carried out. In the course of these, the effects of the modifications on the unusually demanding operating conditions of the Concorde had to be observed. The aircraft heats up when travelling at twice the speed of sound simply as a result of friction between the airframe and the air, and in places the temperature rises as high as 127-oC. Here, the fuel in the wing tanks performs the essential secondary function of distributing the local peaks of heat. The new tank linings must not upset this ongoing equalisation process. It was also necessary to demonstrate that rapid fluctuations of pressure and temperature such as might occur during an emergency descent from Concorde's extremely high cruise altitude of approx. 18 km would not in any way impair the flow of kerosene. Again, the mass distribution and the centre of gravity of the aircraft, which were both changed as a result of the additional tank linings, had to be investigated and accepted also.

Now that the technical requirements for recertification have been satisfied, British Airways (BA) and Air France (AF) have begun the task of restoring their flagships to serviceability. Both airlines require three modified aircraft each simply for the New York routes from London and Paris, while additional airframes of this maintenance-intensive type are used as hangar reserves and for charter operations. At the time of going to press BA was hoping to be able to recommence passenger services by the end of October, AF on 5 November.

It was not simply a matter of having the Certificates of Airworthiness returned, but the external condition of the Concordes had to be restored as well. Thus, all the planes that are to be modernised will be repainted as well as having their interiors refurbished.

Meanwhile BA has reactivated its dedicated Concorde website (www.britshairways.com/concorde). Under the catchwords speed, spirit, ambition and harmony, the company is campaigning to woo back passengers for the Mach 2 aircraft, which no one would doubt constitutes a milestone in aeronautical engineering.

The number of flying hours accumulated in normal operations by the twelve Concordes is relatively low, and, moreover, the high temperature sustained during the cruise at altitude has the effect of reducing the negative effects of corrosion. It is likely, therefore, that many more years of service lie ahead of the Anglo-French joint aircraft. For example, BA's G-BOAF, built in 1979, has accumulated only 17,265 flying hours to date, making it still quite "youthful" in comparison to similarly aged large jets. Although DGAC spokesman Le Houx referred to the detailed structural checks and assessments that were needed for each individual aircraft, nevertheless he thought that another 10 to 15 years of service were entirely plausible.

"The chain of events has now been broken"

Mike Bannister is British Airways' Chief Concorde Pilot. He spoke to FLUG REVUE about the uphill struggle to restore Concorde to passenger service.

FLUG REVUE: What is your present view of the cause of the accident?

Bannister: As in most accidents, a chain of single events was involved. Some of them were particularly improbable. There was this piece of metal on the runway that was made out of titanium, an extremely rare coincidence. It had an unusual L shape and was sticking up in the most unfavourable way possible when Concorde rolled over it, so that it forced its way into the inside of the front left tyre. The tyre then burst in a manner which four different manufacturers say had not been seen in 40 years.

A 1.6m long piece broke off, much bigger than the pieces whose impact modern aircraft have to be capable of withstanding in order to gain certification. The piece caused a reaction in the tank, the like of which was quite unheard of in the civil aviation world. The impact did not cause any puncturing of the tank, but a shock wave which pressed a part of the tank skin the size of a piece of A4 paper towards the outside.

FR: So how exactly did it catch fire?

Bannister: The accident investigators are now reasonably certain that a metal part flew into the undercarriage and severed one or two wires there, causing a spark. This spark then ignited the large quantity of kerosene, and some 100 litres per second poured out. Normally kerosene is very fire resistant. However, in this case because of the large amount the ignition characteristics were altered and it was relatively highly flammable. The flames which burned on the left-hand side had caused considerable damage to the aircraft even before rotation. After take-off they spread further and finally resulted in the crash.

FR: How can one prevent such a sequence of events occurring again in the future?

Bannister: The decision was made to break this chain in more than one place. First of all, the new Michelin tyre is quite excellent and a major step forwards in aviation. I would be extremely surprised not to see this tyre adopted on many other aircraft as well in the future. It is extremely difficult to damage, mainly because there is a coat of Kevlar below the surface area. The aviation authorities insisted on destroying it, but this was extremely difficult. As a result we can provide assurance that, if the tyre were to burst, only very small pieces would be torn off, and these would fly off at a very low level of energy, less than 30% of the energy that would have been released on previous tyres. The main reason for this is that the new tyre is under much less pressure than the old ones. This new feature alone would prevent a repeat of the accident.

FR: But you are taking other actions as well.

Bannister: Yes, we are lining the tanks at those points where there is a potential hazard with 82 Kevlar-rubber elements per aircraft. These act like a kind of second shell. If a tear should occur in the outer skin, it would no longer be possible for very much kerosene to escape. Finally, to eliminate any risk, we have relocated the cables in the undercarriage area either to different positions or else fitted the wiring with protective casing made of the latest Teflon material. The Teflon in turn is covered over with a flexible coating of thin steel. Together this ensures that it cannot be torn open or severed.

FR: How do these changes affect Concorde's flying characteristics?

Bannister: Previously we had only computer models, and these predicted minor modifications to the previous situation. After two test flights out towards Iceland we were able to establish that the aircraft's flying behaviour has in fact been far less affected than we had predicted. The changes have had absolutely no effect on the crucial ability of the kerosene to cool down the outer skin during supersonic flight. The tank lining raises the gross weight by around 400kg, but on the other hand the new tyres together weigh 160kg less. Added to this, the new BA cabin furnishings out of carbon fibre and titanium combined with the new toilets weigh 350kg less than the old ones. At the end of the day we are thus lighter than before and we have not had to take out any seats, as was discussed for a short time. On the other hand, during the initial phase of a Concorde flight every aircraft has over 100kg of moisture on board which has collected while it was on the ground and only slowly disappears again thanks to the heat generated during supersonic flight.

FR: How did you keep the crew flightworthy?

Bannister: I have seven flying instructors and five flight engineer instructors, and they kept their skills up-to-date by flying twelve times a month on the flight simulator. The 18 pilots and 15 co-pilots have in the interim been flying the types on which they had previously served. As for the 17 flight engineers, those with appropriate qualifications worked on the Boeing 747-200 and the rest worked on ground-based engineering work for Concorde. We are now bringing them all back to the Concorde cockpits. At present we don't need to train any extra personnel. We have 14 complete crews for seven aircraft.

Normally it takes a pilot six months to train to fly the Concorde, but even the refresher course now lasts around three months.

FR: How many test flights are necessary before you can resume scheduled services?

Bannister: The group of already re-qualified pilots are currently flying five operational assessment flights. Four of these involve flying halfway to New York and back, and the fifth will land in New York. The aim of these flights is no longer to test the aircraft but procedures on the ground and in the air. The cabin is fully occupied with BA staff who won their tickets in an in-house draw. Once these flights are completed, we expect to offer a daily Concorde scheduled service to New York from the end of October. To ensure that we have sufficient standby capacity, this will require three upgraded aircraft. The first plane to return to service will be G-BOAF, which is already finished. G-BOAG and G-BOAE will then follow.

FR: What are your long-term plans?

Bannister: Once we have five upgraded aircraft, we will probably add Barbados to the flight schedule in December, and as soon as all seven planes are available, there will then be two daily flights in both directions between London and New York, at some point early in 2002. Tickets will probably be more expensive than before Concorde was grounded, as First Class prices have gone up since then.

FR: Are you sure that enough passengers will still want to book Concorde flights?

Bannister: Concorde is a beautiful aircraft, but the main reason that we are flying it is that our customers want us to. Around 100,000 passengers fly on Concorde every year. That figure has been pretty constant ever since we began. 80% of Concorde passengers are business travellers and 80% of those in turn are frequent flyers of Concorde. We have maintained very close contact with the 1500 top customers and also personally shown them the modifications. Most of them can't wait for us to resume flights.

Mike Bannister was talking to Andreas Spaeth

From page 22 of FLUG REVUE 11/2001