Act of God “Tragedy at Gonesse”

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On 25 July 2000 at 1443 GMT, the tyre of the number 2 wheel of Concorde F-BTSC burst during take-off. This set in motion a train of events that resulted in the destruction of Concorde 203. Two minutes after starting the take-off roll, the aircraft crashed on to a hotel at Gonesse, 8 km to the west of Charles de Gaulle airport, with the tragic loss of all 109 people on board, 4 on the ground and injury to 6 others.

At first the Civil Aviation Authority did not withdraw the Concorde’s Certificate of Airworthiness. However after pressure from the equivalent French authority, the Direction Generale de l’Aviation Civile (DGAC), Concorde was grounded by both countries. Because of Concorde’s revolutionary aerodynamics and speed range, these requirements were often more stringent than those of subsonic aircraft. With respect to an engine failure during take-off, TSS required that the climb gradient should be 4% or more whilst climbing at the engine out safety speed V2; in comparison to 3% for subsonic aircraft at its V2. The reason being that the performance of the slender delta deteriorates more sharply when an incorrect speed is flown compared to a conventional swept wing.

The maximum all up weight on take-off is limited by:
1. Maximum structural weight, just over 185,000 kg for Concorde.
2. Performance. The limiting case being when at decision speed-V1- is just fast enough to allow a safe climb out at V2 with one engine failed and at the same time just slow enough to stop before the end of the runway. Length of runway, height of obstacles to be overflown just after take- off, headwind, atmospheric pressure and temperature vary the maximum weight, furthermore, a wet slippery or snow-covered runway would reduce performance.
3. Tyre speed limit, peculiar to Concorde. The limit here is 250 mph (220 knots) and can be a factor when the ground speed on take- off is high, due to heavy weight, flying from a high-altitude airport or when there is tailwind.
4. Noise abatement, also peculiar to Concorde. Special graphs were drawn to show the maximum weight for particular runways at New York from which a Concorde would not exceed a given noise reading.
5. Centre of gravity position. Provided all the tanks were practically full, save tank 11 at the rear, it was allowable to have the centre of gravity at 54% rather than 53.5% (percentage of the root chord of the wing). Thus 5 1/2 inch rearward positioning of centre of gravity improved the performance allowing around an extra tonne to be carried- provided limits 1, 3 and 4 were not exceeded.

Weight restrictions due to performance considerations could reduce range and/or payload. Should the wind suddenly change, causing take-off weight restriction, an alternative runway might have to be requested. At Charles de Gaulle, this could entail 4.2 km taxi from 26R (runway two six right) to 08L(reciprocal runway zero eight left). If required a weight reduction can be achieved by burning off the excess fuel before take-off; at idle thrust losing about 100 kg per minute (compared with about 1,400 kg per minute at full take-off thrust).

Using actual take-off weight from the load sheet, the ‘V’ speeds are confirmed:

V1 is the ‘decision’ speed. If there was an engine failure at, or less than, V1, the take-off could (and had to) be safely abandoned. Once at V1 or above, the take-off had to be continued, there being sufficient runway from which to get airborne. V1 for Concorde fully laden was typically 160 knots.

The next speed Vr (velocity rotation typically 195 knots) when the control column is pulled back to ‘rotate’, that is, pitch up the aircraft with respect to the horizontal. On Concorde with all engines operating, the rate of rotation required was 2 degrees per second to a pre-set angle of pitch θ2 (‘theta two’- the angle of pitch, or the angle of the fuselage to the horizontal, that must be flown after take-off, which is typically about 13 degrees). Approaching 250 knots the aircraft is pitched up again to maintain that speed, for the noise abatement procedure. Should an engine have failed at V1, the rotation rate (still initiated at Vr) is slightly reduced. The aim now is to achieve V2 (the engine failed climb speed typically 220 knots) and a pitch of θ2 simultaneously.

V1, Vr, V2 and θ2 are determined for each departure. Flight AF 4590 from runway 26R, dry surface, calm conditions, temperature 19 degrees C (66 degrees F), pressure 1008 millibars, was limited by the maximum permitted structural weight of 185,070 kg (407,154 lb); V1 was 150 knots, Vr 199 knots, V2 220 knots and θ2 was 13 degrees. Concorde generated lift at high angles of attack (in excess of 7 degrees) due to the formation of vortices over the wings. These gave lift at the expense of increasing induced drag (drag due to lift). The slender delta wing, at even higher angles of attack (over 16 degrees), did not stall conventionally but exhibited another phenomenon- it could generate more drag than there was thrust available. When thrust and drag were equal, the aircraft flew level, in other words it had zero rate of climb. With maximum available thrust, the speed at which this occurs is known as Vzrc (velocity zero rate of climb speed).

Following an engine failure at V1 the subsequent climb profile is fixed using a compromise between climbing to clear immediate obstacles (using extra or ‘contingency’ thrust) and accelerating the aircraft to a speed well in excess of Vzrc. Inability to accelerate was a major factor in the Gonesse accident.

 The following table gives the figures for Vzrc at a weight of 185 tonnes:

Velocity Zero Rate of Climb (Vzrc)

Gear retracted

193 Knots 262 knots
Gear extended 205 knots

>300 knots

Concorde crews were very conscious of this phenomenon. For optimum climb performance on three engines, Concorde had to be flown with zero side-slip, in other words straight into the oncoming airflow. There was a side-slip indicator beneath the compass (horizontal situation indicator). If a left-hand engine failed, the aircraft would point to the left, and without rudder input, slip (or crab) to the right. Application of right rudder stopped the slip, but due to asymmetric thrust there was a small residual turn to the left. This was arrested by applying about 2 1/2 degrees of right bank.

 

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Cockpit

 

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Pilot’s instrument panel with flight director

 

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Fuel Tanks on the Concorde

The centre of gravity for take-off was usually at 53.5% along the wing root chord. 1% is about 11 inches (roughly 27 cm). The position of the ‘zero fuel centre of gravity’ was entered on the computer on the Flight Engineer’s panel. This figure was derived from the disposition of the payload, pantry    (meals) and crew. The computer then summed the fuel from the 13 tanks (numbered 1 to 11- there was a 5A and a 7A) and produced the actual centre of gravity. Most often this was at variance with the 53.5% required. If it was forward of 53.5% then fuel was transferred to the rear tank 11; to the rear of 53.5% then fuel had to be transferred forward. In this condition all the forward tanks were full so there was space to complete the transfer only after the engines had used some fuel during taxiing. Therefore a pre-calculated amount of fuel had to be burnt. Should the centre of gravity have been in excess of 54% on engine start-up, it was allowable to use 54% for take- off. A rearward centre of gravity gave ‘flap’ effect at the expense of making the aircraft less stable. Stability with full tanks (apart from number 11) was not compromised. The flap effect was put to use since it improved a performance limited take- off weight by about a tonne.

On the morning of 25 July 2000, the number 2 engine of F-BTSC had an unserviceable thrust reversed unit. Although Concorde was allowed to depart, once the unit had been safely locked, it incurred a performance penalty, which reduced the range. The captain requested the unit be changed on spite of the delay. It all became part of the intense media speculation over what caused the ensuing tragedy.

The following day, BA resumed its Concorde flights. Even tiny events of no consequence became the focus of enormous press interest. Because the cabin crew detected a faint smell of kerosene in the galley, one New York- bound Concorde diverted to Gander in Newfoundland. Before the accident, such a diversion might not have been warranted. The media was ready to pounce and the Concorde crews knew it.

Questions were already being asked. Had the recently reported hairline cracks in the wing caused the disaster? Did the last-minute change of the thrust reverser cause an engine to catch fire? Study of the photographs taken of F-BTSC on departure revealed a burning wing. How had a fuel tank been penetrated? The subsequent investigation was to produce four reports and take 18 months to complete. On 27 July the Bureau Enquetes Accidents (BEA) issued the first of 14 bulletins:

Shortly after V1, the ‘Tower’ (Control Tower) reported seeing flames coming from the rear of the aircraft. Engine number 2 appears to have lost thrust (noted by the crew) followed later by number 1. The undercarriage would not retract. Speed and altitude remained constant and the flight lasted for about a minute. After banking sharply to the left, the aircraft crashed. The remains of tyres were found on the runway, debris was found along the flight path and in a small area at the crash site.
A preliminary report would follow at the end of August. The bulletin made two further points. The first mentioned that British, German and American investigators would be included under the auspices of BEA. The British equivalent to the BEA is the Air Accident Investigation Branch (AAIB). The second point acknowledged the role of the French judiciary, whose task was to take action should the law have been broken. In France any evidence is ‘owned’ by the judiciary which can take advice from the investigators. In the UK the evidence is ‘owned’ by the investigators who work in parallel with the coroner or Board of Inquiry. The investigator’s remit is not to apportion praise or blame. By preventing early analysis of some parts of the wreck, the AAIB felt that the French judiciary had impeded the investigation. This represented a contravention of ICAO (International Civil Aviation Organisation) Annex 13 to which France is a signatory. On 28 July the second bulletin appeared. Paraphrased it stated that:
. . . debris found on runway 26R came from the Concorde’s left- hand side including remains of two* (of the four) tyres from the left gear leg. No engine debris was found and evidence suggested that he fire was external to the engines.

 

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Tyre debris found on the runway

* subsequently proved to be just one

 

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On 30 July the third BEA bulletin released more details, including that of the discovery of a portion of fuel tank on the runway. The judicial authority retained this piece. The polythene bag in which they had sealed it became opaque from being handled. Actions like this, said the AAIB, had delayed the investigation. A tyre burst causing a fuel leak, which was somehow ignited, now appeared as the most likely explanation for the accident.

The fourth BEA bulletin, on 1 August, defined the seven areas of investigation for the Commission of Enquiry ( presided over by M Alain Monnier)

Site and wreckage
Aircraft, systems and engines
Preparation and conduct of the flight, personnel information
Flight recorders
Aircraft performance
Witness testimony
Examination of previous events

 

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Strip of metal that fell off from preceding aircraft on the runway

From the fifth bulletin on 4 August came the announcement that a metal strip about 40 cm long, not belonging to the Concorde, had been found among the debris on the runway. Was this the cause of the tragedy? How did such an object come to be on the runway in the first place? The answer to the first question appeared to be ‘more than likely’. The second question was not answered immediately, but started a debate about runway inspections. The requirement was three times daily. Then it transpired that, due to a fire practice on 26 R (runway used by F-BTSC) and 26 L, the second inspection had been delayed. On 16 August the eighth bulletin announced that Concorde’s Certificate of Airworthiness had been suspended on the grounds that such an event might easily happen again.

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The previous day BA had been warned by the CAA of the imminent suspension of the Certificate of Airworthiness. For everyone involved with Concorde, having operated it safely for nearly 25 years, this was a bitter blow. There had been occasions involving tyre deflations but following the incident described below, these had been satisfactorily addressed. By 1993, following further modifications, tyre incidents were practically eliminated.
What had been the most notable tyre burst happened to Air France Concorde F-BVFC on 14 June 1979 at Washington Dulles. The cause was not established. During taxiing before take- off, a main wheel tyre deflated probably due to faulty ‘fusible plugs’. They were fitted to prevent an overheated tyre from exploding. The neighbouring tyre on the same axle row now bore twice its normal load for the whole of the take- off run (there were two axles and four wheels on each of Concorde’s two main legs). According to TSS the overloaded tyre should have coped. In this case Vr (rotate) speed would have been about 190 knots.

On take- off, the slender delta wing did not give lift until there was a distinct angle of attack. On take-off the conventional swept wing starts to give lift as soon as the speed builds. During the take- off run, the wings of a B747 start to give lift at a speed below Vr (rotate) and curve upwards; this reduces the weight that is carried by the wheels. With Concorde at Vr, the wheels were momentarily forced into the ground so bore a force somewhat greater than the weight of the aircraft. This resulted in the extra- loaded tyre bursting. Debris from the wheel rim penetrated the tanks, damaged some hydraulic piping and caused a fuel leak of 6 litres per second (one-tenth of the average rate of the Gonesse accident). No fire followed. (At full thrust and with reheat an Olympus engine uses over 7 litres per second.)

To prevent an incident similar to that at Washington, Concorde was fitted with stronger tyres and wheels, improved protection for the hydraulic pipes and a tyre deflation detector. The detector worked by sensing the twist in the undercarriage bogie beam. Should a tyre have deflated in the speed range do 10 to 135 knots, this failure would have been signalled to the crew and the take- off stopped. This system avoided exposing the neighbour of a deflated tyre to the major part of the take- off run. Concorde had been flying for almost 25 years; however, the 84,000 flight cycles achieved equalled those flown by all the B737s in a matter of weeks. Even if it were considered statistically impossible to repeat the crash circumstances, the authorities had little option than to call for the suspension of the C of A until appropriate modifications had been carried out. Some argued that the lower wing skin was too thin to withstand impact and that the expense of strengthening it would be prohibitive. Others pointed out that self- sealing tanks had been used in the Second World War. Nobody doubted that a remedy was possible, but would it be cost- effective?

On 31 August the preliminary report was published. Its summary read:

During take- off from runway 26R at Roissy Charles de Gaulle Airport, shortly before rotation, the front right tyre of the left landing gear was damaged and pieces of the tyre were thrown against the aircraft structure. A major fire broke out under the left wing. Problems appeared shortly afterwards on engine number 2 and for a brief period on engine number 1. The aircraft was neither able to climb or accelerate. The crew found that the landing gear would not retract. The aircraft maintained a speed of 200 knots and a radio altitude of 200 feet for about one minute. Engine number 1 then stopped. The aircraft crashed on to a hotel at La Patte d’Oie in Gonesse.

The preliminary report that extra baggage had been loaded but not properly accounted for; the ‘ground ‘ copy of the load sheet could not be found. Only 800 kg of the two tonnes of fuel loaded for the taxi has been used. The extra baggage and fuel made the aircraft at least one tonne over structural weight for take- off, although this resulted in a negligible difference in performance.

The centre of gravity on engine start was 54.2%, which after taxiing had moved forward to 54%. The report told how data from the recorders had been retrieved. Ten seconds before the start of the take- off run, the cockpit voice recorder (CVR) reveals that the tower informed the crew of a tail wind (easterly at 8 knots) and cleared AF4590 for take-off. If this were a steady wind, then due to the tyre speed limit, the aircraft’s performance weight was too great by about 5 tonnes. The crew did not audibly discuss this. In reality the average wind was very light from the north-east. The report said:

at 1444, the average wind at the threshold of runway 26 was 020/3 kt and 300/3 kt at the threshold of runway 08. (the reciprocal runway). All goes normally to V1- 33 seconds after start of take- off. Six seconds later, at 175 knots, there is a noise and a second later a change in the background noise- the ignition of the fire and engine surge (akin to a backfire). One second later, at 185 knots, the rotation is commenced.

 The report shows pictures of the 43 cm x 3 cm strip of metal that cut the tyre from shoulder to shoulder, and the piece of damaged tyre itself, measuring 100 cm x 30 cm and weighing more than 4 kg. The profile of the cut corresponds to that of the metal strip. On visual inspection the metal strip appeared to be a light alloy. There is no mention of where it could have come from. The photograph of the 30 cm x 30 cm portion o fuel tank found on the runway shows that it suffered no impact damage bit it was slightly bowed outwards. The mechanics of its ejection from the lower wing surface are not discussed.
There is a runway diagram showing where the debris was found, the tyre marks of the left-hand undercarriage and trail soot from the fire. Both the strip and the tyre debris were found together on the north side of the runway. This puzzled Alan Simmons, an investigator from the AAIB. Had someone put them together? Why the rotation was commenced some 15 knots below the calculated Vr has not been satisfactorily explained even in the final report which was published in January 2002.*

*the rate of rotation was slow, about 1 degree per second possibly in compensation.

Immediately after rotation there is evidence of an explosion when a piece of concrete (10 x 25 cm and about 1 cm thick) was detached from the runway probably where the two left engines surged simultaneously. The increasing angle of attack changes the airflow pattern under the wing. This caused the hot gases to be ingested into the engine via the auxiliary intake, behind the main intake in the floor of the ducting to the engine. The double surge gave the aircraft an impetus to the left, causing the left gear to strike a runway edge light before becoming airborne.

In conjunction with the physical evidence, the ‘traces’ of the flight are read and are shown in the report. Each ‘trace’ plots, with respect to time, a parameter: airspeed, pitch angle, engine thrust and other data. When the Black Box or Flight Data Recorder (FDR) reads 97602.5 seconds, which equates with 41 seconds from the start of take-off, there is a sudden decrease in acceleration. Fractionally later there is a strong lateral acceleration to the left (the double engine surge), which is countered with the application of right rudder. On rotation, the runway’s centre line becomes progressively obscured. Without the visual cue the captain maintains runway heading on his compass while the aircraft continues its drift to the left from the impetus caused by the surges. The final report says the lateral acceleration sensed on the flight deck is less than that at the centre of gravity which helps to explain the lack of track correction.

Within three seconds of the fire igniting and within one second of rotation, the control tower tells the crew there are flames behind them. Two seconds later (45.5 seconds), at 195 knots, nose wheel off the ground and with less than 2,000m of runway remaining, from the CVR the Flight Engineer possibly says ‘stop’ (the take- off). Perhaps he thought there had been a double engine failure, because when he announces ‘engine failure’ there is a hesitation about which has failed. Then he announces ‘shut down number 2 engine’. (The standard procedure would be for the Captain to ask the Engineer to shut down an engine once at a safe height. On this occasion, the situation probably appeared to require instant action.)

One second later, the Captain asks for the Engine Fire Procedure. The fire warning for the number 2 engine sounds, supporting the diagnosis. In fact the heat of the fire outside the engine nacelle has set it off. Meanwhile, the number 1 engine recovers to give almost full thrust. The aircraft struggles up to 200 feet above the ground. The speed barely reaches 210 knots, 5 knots above Vzrc with three engines operating and gear down. If the number 2 had been operating they might have been able to accelerate despite fire damage but with no way of putting out the fire.

In the Northern Hemisphere the wind veers and increases with height. On this take-off, although the wind direction was momentarily due east, the surface wind was generally north easterly and very light. Soon on climbing to the west, their airspeed was not augmented with an increasing headwind, if anything the reverse.
The selections made on the flight deck can be interpreted through analysis of the sound signature of the recorded ‘clicks’. For instance, the pulling of the fire handle can be heard 58 seconds of start of take- off. This occurs just after an unknown source, presumably another aircraft, has told them that flames are large and do not seem to be coming from the engine.

  • The landing gear does not retract.
  • This and the low airspeed ( le badin) are of great concern to the crew.
  • ‘Le badin, le badin,’ calls the First Officer.
  • A toilet smoke alarm sounds; smoke in the cabin?
  • Air Traffic Control offers them ‘an immediate return to the field’.

This would involve a right turn for a landing to the east on the northernmost of the three runways at Charles de Gaulle (runway 09). The First Officer acknowledges. From 88 seconds after take- off the engine fire alarm sounds continuously and the terrain warning system urges them to ‘pull up, pull up’. Then 100 secs after the start of the take- off run, the number 1 engine, which had staged a recovery, surges and fails. The crew elects to try for Le Bourget, which by then is less than 2 km ahead and slightly left.

At 295 knots with the gear down their speed is 100 knots below the two- engine Vzrc for their weight. The aircraft can only decelerate. The rudder loses effectiveness, the aircraft banks to more than 90 degrees to the left and pitches up – the loss of fuel has moved the centre of gravity aft. It turns almost through 180 degrees. In an attempt to level the wings the crew probably throttled back the two right engines. With very little forward speed the aircraft impacts, breaks up and burns. The accident is not survivable.

A Japanese passenger took two photographs of the fire from a Boeing 747 waiting for F-BTSC to take- off before crossing runway 26R. By coincidence Jacques Chirac, President of France was on board. Could the 747 have triggered the early rotation? It was too far away to be a factor, on the last of a group of three taxiways.

Once on fire what else the crew could have done? The final report says that if the crew had tried to stop at the first indication of a problem at 183 knots or when the engineer may have said ‘stop’ at 196 knots, they would have overrun the runway at 75 knots or 115 knots respectively. Maximum braking on seven wheels and reverse thrust on three engines was used in the calculations. Neither course would have improved their chances of survival. The crew could do nothing more than they did; circumstances, through a set of cruel coincidences, had blocked all avenues of escape.

The report gives a resume of the members of the crew, their qualifications and licenses held.

Christian Marty, at 54, had been a Concorde Captain for two years. Previously he had flown the Airbus A 340 and before that a variety of mainly short- haul airliners. He had an adventurous streak. In 1982 he had crossed the Atlantic on a windsurfer. He had refused to sleep on his support boat, preferring to be strapped to his board; therefore he could truly say that he had spent the entire crossing on a windsurfer. On another occasion he flew over a volcano in a hang glider.
Jean Marcot, 50, had been a First Officer on Concorde since 1989. Rather than bid for a command on another type of air raft, he had elected to remain in the right- hand seat of Concorde. In theory his license medical had expired eight days before. The oversight was more administrative than careless. The regulations had recently changed – previously a medical certificate had remained valid to the last day of whichever month it was due to expire. In July 2000 it was only valid six months from the date of the last medical. In November 2000 the rules reverted. He was an instructor on the Air France Concorde simulator.
Gilles Jardinaud, 58, the Flight Engineer, has had just over three years on Concorde.
The preliminary report confirmed the decision to keep Concorde grounded, with this final paragraph:The certificate of Airworthiness of Concorde be suspended until appropriate measures have been taken to ensure a satisfactory level of safety as far as the tyre destruction based risk is concerned.

0n 4 September 2000, the 10th bulletin announced that the metal strip that had caused the tyre burst had fallen from the thrust reverser mechanism of a Continental Airlines DC10. The flight had left for Newark in the United States some minutes before the ill- fated Concorde. The author of the bulletin was at pains to emphasise that Continental had co-operated fully with the investigators.
Several major questions remained unanswered. How was the fuel leak caused? What was the source of the ignition? Why did the landing gear not retract? Did the missing ‘spacer’ in the left main gear cause Concorde to track to the left?

In each main undercarriage on the Concorde there were two ‘shear rings’ whose purpose was to keep the wheels running straight. The rings were kept in position by a ‘spacer’. If the spacer was missing and the undercarriage was retracted, the lower (outboard) shear ring was kept in place by gravity. However, the upper (inboard) shear ring, unsupported by the spacer, would fall a little each time the gear was retracted. Once the ring was displaced the bogie beam could become misaligned by up to 2 degrees in either direction. The bogie beam of the left undercarriage assembly carried wheels 1, 2, 5 and 6. During the accident investigation a BA engineer noticed that the spacer has been missing from the crashed Concorde. How significant was this?

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Path of the Concorde on the takeoff roll on the runway

Captain John Hutchison along with other former Concorde flight crew, suspected that the lack of the undercarriage ‘spacer’ was another factor in causing the aircraft to track towards the left side of the runway. For most of the take- off run there were no discernible rubber deposits from the left gear and none from the right gear. There is, however, a photograph in the final report showing rubber marks from the three remaining wheels of the left undercarriage leading up to the broken runway lamp. The track of the two left tyres (numbers 1 and 5) on the left gear is clearly visible in the photograph. To the right, in the direction of take-off, the marks from the flaying remains of number 2 tyre are visible ahead and to the right of the rear right- hand tyre (number 6) track. This suggests that the left bogie was twisted to the right therefore applying a force to the right. Being behind the centre of gravity, this force would attempt to push the tail to the right and the nose to the left. The left gear would drag more than the right; this too would increase the turning for e to the left.
It seems the rubber deposits begin well after the start of the deviation to the left. The point where the rubber deposits appear could have been where the shear ring, normally kept in place by the spacer, was finally dislodged by the shaking of the flaying tyre. What caused the leftward drift?

Number 2 engine was shut down and the number 1 surged, ran down and took over ten seconds to restore itself to full thrust. In this time 1,000 meters were covered. With such a long period of asymmetric thrust, application and holding of 20 degrees of right rudder would have been necessary. Initially 20 degrees of right rudder is recorded. For some reason (autostab no longer detecting left yaw?) the rudder angle was reduced to, and held at about 10 degrees. In the case of engine failure when airborne it was recommended that sufficient rudder be applied to achieve zero (aerodynamic) side-slip. In this condition the aircraft would turn with wings level in the direction of the failed engine. To prevent this turn about 2 degrees opposite bank is needed. If sufficient rudder only to achieve zero side- slip had been applied and the wings were level, as they would be with the main gear on the ground, crab to the left would have resulted. The lack of the spacer may not have caused the initial deviation; but may have added to it just before lift- off. By how much, if at all, is open to question. According to Alan Simmons of the UK’s Air Accident Investigation Branch, the tracks in the soot suggested that the left wheels had rolled over already deposited soot. Yet the wheels preceded the smoke. Had the wheels been soaked with fuel, which laid a damp trail on which the soot deposited differently? There was a fuel stain on the runway followed by a dry area then the deposits of soot. According to Ted Talbot (former Chief Engineer In Service Aircraft BAe) the piece of tank 5 hinged out, before breaking off. The hinge was inboard on the longitudinal axis. Fuel was first sprayed to the left- onto the runway, then downwards to the gear- not onto the runway, finally igniting- leaving soot on the runway. That would explain the observed evidence.

At some stage there might have been a leak from a damaged hydraulic pipe to the brakes causing a loss of ‘green system’, solely capable of raising the gear. ‘Green’ system was pressurized by pumps on the left two engines. There were two more hydraulic systems: ‘blue‘ was pressurized by the right two engines and was mainly dedicated to the flying controls. The standby ‘yellow’ system was pressurized by engines 2 and 4 and could be selected into parts of ‘blue’ or ‘green’. The French judiciary had acquired the gear leg so the AAIB was not able to ascertain the exact state of the hydraulic pipes to the brakes. The AAIB’s criticism of this practice appeared in the final accident report.

During a gear retraction the main gear doors open first. Until it is up and locked, there is more drag than with it down. Could the First Officer have delayed gear retraction with this in mind? The second time the captain says, ‘le train sur rentre’ the co-pilot replies, ‘le train ne rentre pas’. Is he saying that the gear will not come up because of a malfunction, or because he is leaving it down? If the attempt is made, for some reason the gear does not respond. The red wheel light may have been on to indicate a brake overheat or that a flat tyre had been detected. This could have prevented selection of gear up. In the documentary, some airport firemen suggest that they smelt tyre rubber and that the fire was already alight before ‘SC’ had reached the point where the infamous strip of metal was supposed to be. If this were true the tyre failure could be ascribed to the lack of a spacer allowing the wheels to ‘crab’, overheat and one to burst.

The evidence of the firemen is difficult to corroborate. Did they know where the piece of metal was with such accuracy that they could be certain that the fire had started before the Concorde reached it? Suffice to say that the more verifiable evidence still supports the view expressed by the accident report. Tests were carried out on the about- to- be decommissioned F-BVFC in Toulouse to establish whether the lack of spacer was relevant. Apart from risking damage to what was now an irreplaceable museum exhibit, the test could not possibly reproduce the exact conditions of the day- the engine surges, the bursting tyre and so on.
Another conjecture concerns the question of the ‘early rotate’. There was neither a call of ‘rotate’, nor of ‘contingency’. Contingency (extra power) is automatically applied if one of the engines fails to give sufficient thrust. The flight engineer, if he spotted an engine problem once V1 was passed, would manually select contingency thrust and announce that he had done so. It is possible that the captain on hearing the words ‘engine failure’, reacted by rotating the aircraft. On rotation he simultaneously applied right rudder to keep straight, and then, with the runway obscured by the nose, reduced the rudder deflection to fly with zero side-slip. This might explain why the rudder is relaxed from 19 degrees and held at 10 degrees. The crew found themselves in an entirely untrained-for set of circumstances; they heard calls referring to ‘long flames behind you’ amidst a cacophony of warning sounds which rendered themselves uninterpretable.

In such a scenario it is possible that a previously learnt ‘conditioned reflex’ took over. Captain Marty had started his career flying twin jets. On a powerful twin jet, V1 (decision speed) is well in excess of Vr (rotate speed). It would be impossible to stop once airborne, so V1 is limited by Vr. Every six months on the simulator pilots practice having an engine failure on take-off. The most difficult moment for this to occur is just as soon as the runway ahead disappears from view. So routinely every six months the candidate on a twin jet practices rotating and keeping straight following an engine failure. On four engine jets there is usually a gap between V1 and Vr, typically of about 30 knots on Concorde. If a conditioned reflex had takes over, it might explain why when rudder was applied, the rotation was irresistibly initiated- 15 knots too soon.

In no way are these remarks intended to apportion blame, they are written to suggest why certain events occurred, and what can be done to prevent a similar accident. The crew of ‘SC’ was faced by a cruel set of circumstances. Even with unlimited time it is difficult to suggest a better way of handling the incident; the crew of ‘SC’ only had seconds.

Through courtesy of :

9023

 

 

 

 

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