Letters to EASA
15th April 2008
Mr Claude Probst, Rulemaking Director
European Aviation Safety Agency
Postfach 10 12 53
D-50452 Köln Germany
Dear Mr Probst,
Subject: Fuel Tank Flammability.
Thank you for the reply to our letter on the subject of Fuel Tank Flammability. It is comforting to know that EASA places a high priority on this subject and has initiated a programme to improve flammability However, we are more concerned at present about the problems in the existing fleet. The main point of our recent letter relates to the high levels of fuel tank flammability in Boeing 737 and 747 aeroplanes, both models having experienced fuel tank explosions in the past. The reason why these aeroplane types have high flammability tanks is that the aircraft air-conditioning systems can heat up the centre wing tanks, thereby making them more likely to explode in the presence of an ignition source. Whilst there can be no dispute that making modifications to reduce the likelihood of an ignition source occurring is most beneficial, recent thinking on the subject of fuel tank safety considers that reducing the probability of an ignition source to zero is, practically, unlikely, no matter how many improvements are made.
So far, it appears that the FAA has not addressed this unsafe condition, which is exhibited by the B737 and B747 aeroplanes. Despite the production of the NPRM mentioned in our last letter (FAA Docket No. FAA-2005-22997) and which when implemented as a Final Rule may result in some reduction in the flammability for these aeroplanes, nothing has happened yet.
It is the Air Safety Group's (ASG) opinion that the primary responsibility for dealing with the high flammability of these aeroplanes rests with the FAA, but if this corrective action is not being accomplished, it falls to all other National Aviation Authorities to consider whether they are satisfied with the current safety of B737 and B747 aeroplanes registered in their respective states. This additional responsibility is all the more pressing, given the high profile that the TWA 800 B747 and other accidents have generated.
We have repeated the questions that were in our earlier letter and added some additional words, which it is hoped will further clarify the intent of these questions, this in an effort to amplify our major concerns.
Has the FAA given EASA any information which shows that the continued operation of the B737 and B747 models is safe despite the high flammability of the centre wing tanks?
Following the three accidents (Philippines Boeing 737 in 1990; Boeing 747, Long Island in 1996 and Thai Boeing 737 in 2000), investigations showed that the temperatures in the centre wing tanks at the time of the explosions were considerably above the fuel flashpoint. At these higher temperatures the probability of having an explosion is much higher than for tanks that are kept cooler. The overall experience of the civil jet fleet corroborates this point, since only Boeing models, as far as we know, have had such fuel tank explosions. Noting that no flammability reduction for these aeroplanes has yet been apparent, the ASG would like to know whether the FAA has provided any information which shows that the unsafe condition caused by the high flammability tanks has been controlled in some other way and we would expect EASA to be pressing the FAA on this point.
Are any operational conditions imposed to reduce the flammability of the tanks? (We are aware that operational measures are taken to counter extremely cold fuel temperatures and we believe that at one time additional fuel had to be carried to keep high fuel temperatures down).
The ASG recalls that the FAA did introduce Airworthiness Directives (ADs) to require additional fuel to be carried, which has the effect of not allowing the high tank temperatures to be achieved. Whilst this may provide safety benefits, it does introduce commercial penalties and for this reason, this safety measure may not still be in place. The ASG would appreciate and very much like to receive clarification on this point.
Is EASA satisfied with the FAA position?
Whether or not the FAA has made any representation to EASA on the subject of the flammability of the B737 and B747 aeroplanes, the ASG does not know. We are of the firm opinion that EASA needs to be satisfied by whatever the FAA position may be, and that EASA should have its own position about the acceptability of continuing to operate these aeroplanes - see Question 4 below.
How does EASA consider that continued operation of these aeroplanes remains safe?
The ASG has the impression that fuel tank flammability is regarded by the FAA as a problem that needs to be solved for new aeroplanes, hence the proposals contained (largely) in the NPRM. In practice, it is very unlikely that aircraft constructors could have missed the flammability message, which comes out loud and clear from the various accident investigations, which is 'Keep The Tanks Cool'. But this appears to do nothing to alleviate the potential, continuing flammability problem for the aeroplanes types that have had these fuel tank explosions. The ASG would like to be assured that some action is being taken to correct the unsafe condition that exists with these aeroplanes, but is concerned that this action is not currently in place.
Thank you for your continued attention.
Yours Sincerely
Capt R Williams FRAeS
Chairman, Air Safety Group
+44 (0) 1823 430161
Copies to: Y Morier, Mr M Bell, CAA and the European Commissioner for Energy and Transport
