Concorde’s return to service is imminent

 - May 8, 2008, 5:59 AM

British Airways (BA) flew a modified Concorde to Shannon, Ireland, on August 7 before conducting refresher crew-training operations last month. As many as 35 takeoffs and landings were to be flown as the airline prepared for a possible resumption of scheduled services, perhaps before next month.

BA and Air France are hoping that British and French regulators soon will re-issue the supersonic airliner’s certificate of airworthiness, which was withdrawn following the loss of an Air France Concorde shortly after taking off from Charles de Gaulle Airport on July 25 last year. All 109 passengers and crew and four people on the ground died in the accident. European manufacturer EADS, the design authority for Concorde, was expected to submit a formal application at press time for the grounding to be rescinded.

The crash occurred after a massive fuel leak developed from a wing tank that had ruptured following a tireburst. In an interim accident report in July, Bureau Enquetes Accidents (BEA) safety investigators said “ignition of an air/fuel mixture in the left dry bay caused violent overpressure.” The officials are still analyzing the fuel-tank rupture mechanism, having been unable to confirm an earlier hypothesis that the original puncture followed internal over-pressure after the wing was struck by tire debris. Investigators have formally excluded maintenance and crew actions and decisions, as well as weight considerations, as causal factors.

Following introduction of “viton-impregnated Kevlar” liners (designed to inhibit leaks from damaged fuel tanks), new puncture-resistant tires and hardened wiring harnesses, the first modified Concorde was used for fuel-system trials in late July. BA has been optimistic that the changes will not compromise performance, despite earlier fears that a whole row of seats would need to be removed to offset the extra 880 lb weight of the modification. Now, it is thought that lighter tires and cabin-interior fittings will achieve the same result. Although analysis of test results is not yet completed, BA Concorde chief pilot Mike Bannister claimed the modification has a “negligible” effect.

The July test flights confirm fuel consumption and aircraft range with the reduced tank volume. Five tanks were run dry to check the new usable volume. Concorde’s range has always been marginal on transatlantic operations–air-traffic priority is given to Concordes over land because of their higher fuel consumption (and noise nuisance) at low speed. One BA senior Concorde captain was fired after landing at London with less than minimum fuel reserves.

After last month’s refresher flight, the British airline plans four assessment operations to reestablish customer-service standards and to perform additional crew-training operations. BA hopes to resume service this month, while Air France plans a more conservative schedule starting next month, with the actual dates being driven by the time taken for modification.

What Went Wrong?
The interim accident report reveals “a rapid degradation” of alloy mechanical properties in most of the airframe, with “splashes of melted aluminum” on recovered aircraft parts. Because one main gear door did not open, the undercarriage could not be retracted, contributing to high drag.

Engine teardown and data analysis show the powerplants ran normally. Early power loss on the number-one engine likely followed ingestion of tire debris, and takeoff thrust reduced further, following ingestion of fuel and “hot gases.” Power was restored to almost normal thrust before the ingestion of “hard objects” and hot gases and fuel caused a final power drop. The number-two engine was shut down during routine fire procedures, an action that officials said was justified by an “almost total loss of thrust” and a fire warning.

Flight-planning data, taking account of runway characteristics and a number-two thrust-reverser repair, confirmed that estimated takeoff weight was below allowable maximum limits. Low fuel consumption during taxiing left the aircraft over limits, but “this does not change aircraft performance on takeoff.” Taxi tests with Concorde tires over a metal strip similar to one found on the runway after the accident reproduced damage like that found on one crash tire. The omission by maintenance staff of a bogie spacer on the landing gear “did not contribute” to the accident, investigators said.