|G-BOAF in the majors dock, with modifications still ongoing at Heathrow|
Initially British Airways had said it would take 5-6 weeks to complete the tank liner modification on G-BOAF, this estimate proved just a little too optimistic. From the day the tank liners arrived it had been clear that although they had been designed to fit the Concorde design, they would not all fit into Alpha-Foxtrot, as each Concorde had been near enough handbuilt and was individually different from its sister ships.
When the airline's engineers went into the tanks, they went into areas that they had never needed to be in before. Although the drawings for Concorde were technically accurate, it was found that as the different production aircraft had been built slight diferences had been made. Most of these differencies were small, such as a reposition or shortening certain structures inside the tanks to save weight, but this made the engineers life a nightmare at times.
On more than one occasion, individual liners had to be returned to the manufacturer to be modified or re-made completely:
"It's been very frustrating, there has been a lot of hard work been put in and its not been quite right, we've had to scrap a piece (of liner) and thats been quite demoralising." Keith Milner, an engineer at BA, told a TV crew.
"We think we've made it fit, we've sent the information to (EADS in) Toulouse and they've said that its not quite right and it needs to be done again."
Fortunately for the engineers, the testing that had been carried out showed that the tank areas that were understood to be vulnerable near the engines and landing gear were much less than had previously been thought. Along with the positive results from the initial tests on the new Michelin tyres, it was a relief to find that only 78 liners, of the original124 planned, need not be fitted. 25% of the fuel tanks would now be lined compaired to the original conservative estimate of 40% of the fuel tank area. Although this would not speed up the current prototype mod, it would help on subsequent aircraft.
A further twist in the modification process took place after the first set of liners had nearly been completely fitted, "there are small holes in the liners to allow fuel to circulate between them and the wing skin to allow cooling" Jim O"Sullivan told Flight International,
"The problem we had is that they were too big."
The holes are a compromise between a major leak rate and still allowing fuel to circulate correctly for cooling purposes.
"The liners were removed, patched and then had smaller holes drilled in them"
On Alpha-Foxtrot all the liners needed to have some for of re-work done on them, As time progressed this figure would settle down at 15% of the total liners on subsequent aircraft.
An NZG tyre is tested.
A few weeks later on the 10th of April 2001 the DGAC (The French civil aviation authority) announced that it had authorised Air France Concorde F-BTSD to fly from Paris, to Istres to undergo tests with new technology tyres. In the weeks previously the Air France engineering staff had completed the D check on the aircraft and performed a high speed taxi test on the runway at Charles De Gaulle airport. With temporary authorisation to fly being granted the aircraft would carry out a post modification subsonic airtest.
Sierra-Delta Depart for Istres as AF373s
A week later the stage was set for Concorde to return to Istres. Concorde 213 took off as AF374 from Paris CDG at 11h35, commanded by Air France training captain Andre VERHULST along with First Officer Jean ROSSIGNOL and Flight Engineers Andre CZMAL and Alain PICCININI. Sierra Delta arrived at Istres at 12:23 to start a set of test on the newly developed Michelin NZG tyre technology
In a similar fashion to the leak test in January, the aircraft is accommodated in a hanger at Istres, who also assisted by providing ATC support for the tests. Maintenance of the aircraft would again be looked after by a team from Air France.
At this stage the only tyre certified for use on Concorde were the traditional design used in the Goodyear and Dunlop tyres. The aircraft had transited down from Paris with the standard Air France Goodyears fitted to all 8 wheels on the main landing gear. For the return flight these would be re-fitted regardless of the test results, as the Goodyears were the only tyres the aircraft was certified to use. The main objective of the test would be to test in different conditions the performance of these tyres against the new Michelin NZG tyre.
Concorde features an anti skid system that is regulated from the nose wheel. This system was calibrated from the current data on the Dunlop and Goodyear tyres used by the airlines. To recalibrate the anti skid protocols, tests would have to be carried out not only on a dry, by wet runway.
It would be possible to fit different tyre types to different positions of the bogie, to allow a comparison to be made. Eg Goodyear's on the front and NZGs at the rear. Along with the different tyres, special sensors were be fitted to measure the deceleration being provided by each individual tyre. This procedure would, along with many other things, also the anti-skid protocols to be re-programmed for the new tyre profile.
F-BTSD carries out a wet runway test at Istres
After each "accelerate-stop" run, the data from the test was analysed, and the first conclusions drawn. This made it possible to programme the following tests, and to carry out any recalibration work on the aircrafts systems.
A final ground test was conducted to show how the aircraft would handle undertow with the aircraft at different masses, and using turning circles up Concorde's maximum. This allowed any abnormal deformation in tyres to be spotted if it occurred.
Captain Edgard Chillaud, Test Pilot Pierre Grange and Roger Beral, along with Mike Bannister in the Cockpit of F-BTSD
A circuit pattern was flown that incorporated 2 "touch and go" landings, culminating in a hard stop. Mike Bannister from British Airways was invited to be an observer in the cockpit for these circuts, a favour that would late be repaid during a British Airways training session in Ireland.
During these circuits weather condition were most definately not the best for flying, but produced some of the "worst case scenario" weather. This led to even better data being produced from the aircraft landing on a very wet surface....saving the airport fire service a little work!
Everyone involved felt very positive at the end of the tests,
the wet sufrace for the final test had been a welcome bonus and the tyres performed
brilliantly. They tyres were also 20Kg lighter each, so a overall saving of
160Kgs would be made to help off-set the tank liners being fitted that were
expect to add around 460Kg. In the British Airways aircraft this would further
be off-set by the new lighter interiors.
With all the data Michelin and EADS needed at the completion of the tests, F-BTSD was flown back to Paris Orly airport rather than its base of CDG on May 5th.
The reason - the aircraft had recently competed an 18 month D check and needed a repaint and the Air France paintshop was based there!
A shiny aircraft flew back to CDG on Saturday May 30th. The Saturday departure allowed large crowds to turn out at Orly, and see the aircraft depart for an airport that she would not visit on a regular basis.
Just over a month after the end of the first ever flight with the a set of new NZG tyres fitted, Michelin called a media conference in Paris to announce that the new radial NZG tyre would be offered for use on Concorde when it returned to service
|Michelin show off their new NZG tyre at a Paris press conference|
"This (tyre) offers higher damage resistance and substantial weight gains, two key qualities in the field of aviation."
The tyre would be submitted to the regulators as part of the overall package that was being put in place to return Concorde to service.
With the news that the new tyre would be available for Concorde, the working group met a few days later on June 8th. The working group, formed made up not just of the airlines, manufacturers and government officials, but also the regulators, had been monitoring tests on Concorde and said the results are positive, but at this stage it was still too early to put a timescale on when it can go back into service.
"The group considers that work is progressing satisfactorily although it is slightly behind the original schedule," the working group's spokesman said.
The group said tests on a new tyre designed by French tyre-maker Michelin were positive, but that more work was needed on the plane's fuel tanks which are also being modified.
The installation of this internal coating proved more complex than though at the beginning. " The modification of the tanks is almost carried out ", the group stated and that " tests will be able to take place in the coming weeks".
"The manufacturers committed themselves to making the main efforts to finish the tests and to promptly provide their analyses to the authorities ", said the French aviation regulator, the DGAC.
|Alpha-Foxtrot rolls of of the Majors Dock (Discovery Channel)|
Mike Street, British Airways' Director of Customer Service and Operations said:
"The successful completion of this element of the modifications programme marks a significant milestone in our plans to return Concorde safely to service,"
"Tests are still being carried out but we are on track for a resumption of services hopefully later this summer," he added in a media statement.
"The ground tests that G-BOAF will undertake will last approximately two-three weeks, before flight testing begins which will include at least one flight to RAF Brize Norton. "
Testing at Brize Norton was to include a demonstration of running a modified tank dry to see how the new liner mods will react in such a situation. This test is also to enable a recalibration of the fuel quantity indicators and systems.
If testing goes well, the modifications will be replicated in the other six aircraft in its fleet, while Air France, which owns the other five remaining flight ready Concordes, were making good progress in modifying its first aircraft, F-BVFB.