RETURN TO SERVICE - FULL STORY
Chapter 4
The plan takes shape

On December 15th 2000 the Anglo-French working group meet for the 4th occasion, this time in London. The airlines and manufactures were present to present a set of measures that they hoped would allow Concorde back into passenger service by the summer of 2001. This was initially planned to be a 3 pronged attack, with the manufacturers and each individual airline playing key roles.

It was proposed that British Airways would use one of its aircraft, Alpha-Foxtrot, as a prototype for the proposed modifications:

BA Engineer Mark Morley, demonstrates for the media how the liners will fit into the tanks
A moulded "egg crate" style Kevlar lining would be fitted into Concorde's fuel tanks in the areas that were in danger of being hit by debris from a tyre bust. During the accident fuel was estimated to have been flowing out of the tanks at an average of 60 litres per second (after an initial flow rate of 100 litres/sec). Should a substantial leak occur the liners would be sucked down and fill the hole, reducing the flow rate to an estimated 0.4 litres per second, which was deemed to be acceptable.

Each of the 124 liners has to be individually shaped for each separate area of the wing tanks. They ranged from roughly 4-6 ft. long and 1-1.5 ft. wide. Further problems would arise that each aircraft tended to be slightly different to the next, meaning the a liner that fitted correctly to the design at Toulouse may not fit when it arrived in London or Paris.

A team of 40 engineers, working in two 8-hr. shifts, whould complete the modifications in 8-10 weeks. Subsequent aircraft, which would be worked on in pairs, were expected to take less time to modify once installation procedures are perfected on Alpha Foxtrot.

The liners were fitted in the bottom of the wing fuel tanks between the internal spars. The shallow sides of each tray will be attached with bolts directly to the reinforcing structure of the wing skin within the tanks. This procedure required the engineers working inside the confined spaces of the tanks to drill holes, estimated to be 3/16 in. to a maximum of 1/4 in. in diameter. EADS' design engineers had pre-determined the exact spacing between the holes to be drilled in each compartment.

The manufacturers, using advanced computer modelling and physical trials, tested the modifications package. Results of the tests have proved to be "very promising," O'Sullivan said. "The primary purpose is to stop fuel leaking out." The initial plan calls for 124 liners to be fitted into tanks 5 and 8, with certain parts of tanks 1,4,6 and 7 being lined. These were the areas that analysis had shown to be at risk from tyre or other debris being thrown up from the landing gear area, and was roughly 40% of the fuel tank area. The first idea had been to line all the tanks surrounding the gear and engines, but the complex computer analysis proved this to be unnesesary and overkill.

According to investigators, a large piece of rubber impacted the No. 5 fuel tank, produced a kerosene shock wave and high hydraulic pressure that ruptured the tank from within. The liners are expected to reduce the flow of fuel in the event of a puncture to less than 1 litre (0.26 gal.) per sec. The flow of fuel from the wing tank puncture of the Air France Concorde was estimated at up to 100 litres per sec.

O'Sullivan said there would also be "some attenuation" of shock waves as a result of installing the liners. Investigators of the July 25 Air France crash have determined that the breach in the aircraft's wing tank was caused by a shock wave from within the fuel tank.

This occurred when a large piece of tyre, created when the aircraft rolled over a titanium strip during takeoff, hit the aircraft's under-wing skin just forward of the left main landing gear strut. The manner in which the large piece of tire struck the wing skin triggered a shock wave that caused the skin to rupture from within, O'Sullivan said. This sequence of events became calculable and demonstrable through computer modelling.

The liners in place and suspended above the tank base by the yellow coloured brackets
The liners, which were suspended a few inches above the base of the tanks by specially designed brackets, also had some perforation to allow fuel to flow through them. That will allow for a thin layer of fuel between the tray and the aircraft's skin. O'Sullivan said this was important, as Concorde was designed to employ fuel in its tanks to act as a heat skin coolant as well as being used for centre of gravity purposes.

It was also planned to further shield the 115v wiring in the undercarriage area to stop any arcing that would occur if it were to be damaged. Although the source of ignition was never proven this was always suspected to have possibly have been the main cause.

 
The new British Airways Concorde seats

In January 2000, British Airways had announced that they were planning to upgrade the aircraft interiors to a new design for the new Millennium. There had been talk of fitting this during the early stages of the grounding, but with Concorde's future still uncertain in mid-2000, it was put on hold.

Now with a clear plan in place to return Concorde to service it could go ahead, albeit in two phases, as the engineers with the thorough knowledge of Concorde's systems that would be required to undertake the intricate work of fitting the new toilets, galleys and lighting systems were tied up in the important re-certification modifications, so this part would have to wait.

Phase one, would however be relatively straight forward to implement and would be in place for the aircraft returning to service. This would see new seats, carpets and upholstery fitted. The second phase, or Project Rocket as it would become known, would follow once all 7 aircraft were back in service. This would feature the more intricate part of the upgrade .

BA's initial hopes were that the cabin upgrade would save up to 1million a year on fuel cost due to the weight savings, but now it was far more important as it would off-set the weight being added to the aircraft by the tank liners. Concorde should, if all went according to plan, have the same range and performance after everything was in place.

Air France's role in this initial build up would be that of testing. One of their aircraft, F-BVFB, would be flown to the Military test base at Istres in the south of France where, using the long runway available there, ground tests would be conducted. Performing high speed runs along the runway, at up to 175knots, the engineers would study the flow patterns from an inert fluid being pumped from various places under the wing.

The idea would be to see where fuel flowing from a ruptured tank would interfere with the engines or landing gear areas. This would confirm the computer analayis of the fule leaks in real conditions. It would also, to some degree, help understand where tank liners would definately need to be fitted to prevent leaking fuel entering the engines and causing surges or failure.

The other key role was to be played by the airframe and engine manufacturers. They would need to build mock-ups of certain sections of the aircraft to establish where and how the leaking fuel was ignited and to try to replicate the mode of failure in the tank skin by the wave effect that had taken place in the fuel. Rolls-Royce would also run an Olympus engine to destruction to study what effect UN-burnt fuel and hot gasses would have on the engine and how it would recover from any surges that may occur as these have been seen during the tragedy at Gonesse.

Captain Mike Bannisrter shows the media the new liners at Heathrow
BA's Flight Manager Technical for Concorde and its Chief Pilot Mike Bannister was upbeat on the plans ; "A huge amount of effort is taking place on both sides of the Channel and we are beginning to see some really encouraging signs of progress."

He insisted this refit would not have gone ahead unless BA had received very positive noises about the likelihood of winning back its air safety certificate,

Capt Bannister went on to say : "We are keeping our aircraft in tip-top condition. A team of engineers has been keeping the aircraft ready to fly, checking them out every day, running the engines and looking after all the computers. This underlines our determination to fly once more"

Although nobody was talking dates; April or May 2001 was being targeted as a possible date for bringing the aircraft back into service.

G-BOAF in position in the Majors dock at Heathrow
Just before Christmas 2000 and the New Year things stepped up a gear as the first Kevlar liners arrived to be fitted into Concorde G-BOAF which had only a few days earlier been wheeled into the British Airways Concorde Majors Dock at Heathrow.

In March 2001 stage one, of phase one, of the cabin upgrade got underway. Twenty pairs of the new seats arrived for a test fitting in Concorde G-BOAE at Heathrow. These would be fitted in the forward cabin as a check fit, but also to allow people to see the seating in Concorde for the first time. The response was very positive.

Concorde's return to service was well and truly underway, but many questions still need to be answered and would the passengers still want to fly on the aircraft.

In the middle of so much doom and gloom the working group was greeted to some welcoming good news to start the new year; They had been informed very early in their planning that Michelin was putting the finishing touched to a brand new design of aircraft tyre which would be fitted to new Airbus A380 Super Jumbo, that promised to meet the most demanding standards. Could this new tyre be just what the doctor ordered for Concorde?

The tyre's design made it near enough impossible to burst, but if it did burst the debris would be so small that they would pose no threat to the wing structure and fuel tanks directly above. It was nearly too good to be true.

 

Michelin had christened the tyre NZG (Near-Zero Growth). Resistance to disintegrating from a cut in the tread rubber is related to the amount of circumferential growth due to the effects of inflation and centrifugal force at take-off. Conventional cross-ply and radial tyres had circumferential growths of 12% and 8% respectively. The new NZG tyre has only a 3% growth and is effectively burst proof even after being cut completely through

The authorities could have been happy with the modifications that were currently in work, but this new tyre, if available, would be a welcome bonus.

Tests would be needed on this new technology tyre before it could be used on a certified passenger aircraft, but Michelin was now poised to become the forth and important prong in the attack to get Concorde back in revenue service.