Letters to ICAO

27th April 2010

For the attention of:
Mr. M Raymond Benjamin
ICAO Secretary General
999 University Street
Montreal
Quebec
H3C 5H7
Canada

Dear Sir,

Fuel Tank Flammability

Further to a letter dated 1st August 2009 from the Chairman of the Air Safety Group we are writing this joint letter to you to express our continuing concerns about the current situation concerning fuel tank flammability on B737 and B747 aircraft. Following a number of fuel tank explosion events and the preparation by the FAA of an NPRM on the subject of 'Reduction of Fuel Tank Flammability in Transport Category Airplanes', the ASG has made comments* on this NPRM and the resulting Final Rule, which was published in July 2008. Whilst we share the FAA's general concerns about fuel tank flammability, we do have some quite different views about what needs to be done.

The new FAA rule was prompted by fuel tank explosions on Boeing 737 and 747 aircraft in the 1980's and 1990's. As a result, the FAA has now introduced new design requirements for lowering fuel tank flammability on new aeroplanes and will require the retrospective modification of those aircraft which have centre wing tanks and are US Registered. The main purpose of writing this letter to ICAO is that the FAA does not appear to have adequately discharged their duties to inform Contracting States, operating these aeroplane types, of the necessary information for ensuring safe operations. It should be remembered that the two Boeing 737 explosions occurred on a Philippine and a Thai registered aeroplane. It may be of some surprise to the Authorities in those countries to find that the FAA plans to require improvements to ensure the safety of the US fleets, but not theirs.

Looking at the circumstances of the two Boeing 737 and the TWA 800 Boeing 747 fuel tank explosions, it is widely understood that the centre fuel tank in each case was heated to a temperature well above the fuel flash point by the aircraft air conditioning systems located underneath, which have high temperature components. At these high temperatures, the necessary ignition energy to cause an explosion reduces significantly and consequently becomes more likely. NOTE: Although the original fuel tank safety philosophy was largely based upon preventing possible sources of ignition from occurring inside the fuel tank, it has been generally recognised more recently that this has proved practically impossible to achieve. We are concerned that in the same operating circumstances - high ambient temperature, low fuel state, air conditioning running - fuel tanks of Boeing 737 and 747 aeroplanes could be in exactly the same high flammability state as the accident aeroplanes and thereby be most susceptible to any low energy ignition sources.

It is our view that the FAA action should have been categorised as a mandatory continuing airworthiness issue and forwarded to all other contracting states in the context of Annex 8, Part II, Chapter 4, Para 4.2.1. Hence, in our view, steps should have been introduced by FAA Airworthiness Directives (AD) to reduce retrospectively the flammability levels for all in-service Boeing 737s and 747s - not just the ones on the US Register.

We would be interested to learn whether ICAO has any sympathy with this view. The European Aviation Safety Agency has already been informed about our view and is currently considering the possibility of retrospective action to reduce fuel tank flammability.

Thank you for your attention.

Yours faithfully

Mr R Gifford,
Executive Director PACTS

Captain R Williams FRAeS,
Chairman, Air Safety Group

* The ASG comments on the Fuel Tank Flammability NPRM can be found on FAA Docket 2005-22997.

1st September 2009

For the attention of:
Mr. M Raymond Benjamin
ICAO Secretary General

Dear Sir,

Fuel Tank Flammability

I am writing this letter to you as the Chairman of the Air Safety Group (ASG) of the United Kingdom. The ASG is an independent, voluntary organisation whose aim is to promote safety in Commercial Air Transport operations and Fuel Tank Flammability is one of a number of subjects of concern and in which we take a keen interest. We also advise the UK Parliamentary Advisory Council for Transport Safety PACTS) on aviation safety matters. The ASG was actually founded as the result of a campaign in the early 1960s, to stop the use of wide-cut kerosene (Jet B) in civil airliners. The ASG concern then was that the higher vapour pressure of Jet B fuel meant that it was more likely to cause a fuel tank explosion and, in particular, constituted a significantly greater risk of fire following a crash or emergency landing with the obvious adverse effect on safe passenger evacuation.

More recently, following a number of fuel tank explosion events and the preparation by the FAA of an NPRM on the subject of 'Reduction of Fuel Tank Flammability in Transport Category Airplanes', the ASG has made comments* on this NPRM and the resulting Final Rule, which was published in July 2008. The ASG shares the FAA's general concerns about fuel tank flammability, but we have some quite different views about what needs to be done.

The new FAA rule was prompted by fuel tank explosions on Boeing 737 and 747 aircraft in the 1980's and 1990's. As a result, the FAA has now introduced new design requirements for lowering fuel tank flammability on new aeroplanes and will require the retrospective modification of those aircraft which have centre wing tanks and are US Registered. The main purpose of writing this letter to ICAO is that the FAA does not appear to have adequately discharged their duties to inform Contracting States, operating these aeroplane types, of the necessary information for ensuring safe operations. It should be remembered that the two Boeing 737 explosions occurred on a Philippine and a Thai registered aeroplane. It may be some surprise to the Authorities in those countries, to find that the FAA plans to improve and ensure the safety of the US fleets, but not theirs.

Looking at the circumstances of the two Boeing 737 and the TWA 800 Boeing 747 fuel tank explosions, it is widely understood that the centre fuel tank in each case was heated to a temperature well above the fuel flash point by the aircraft air conditioning systems located underneath, which have high temperature components. At these high temperatures, the necessary ignition energy to cause an explosion reduces significantly and consequently becomes more likely. NOTE: Although the original fuel tank safety philosophy was largely based upon preventing possible sources of ignition from occurring inside the fuel tank, it has been generally recognised more recently that this has proved practically impossible to achieve. The ASG is concerned that in the same operating circumstances - high ambient temperature, low fuel state, air conditioning running - fuel tanks of Boeing 737 and 747 aeroplanes could be in exactly the same high flammability state as the accident aeroplanes and thereby be most susceptible to any low energy ignition sources.

It is the ASG's view that the FAA action should have been categorised as a mandatory continuing airworthiness issue and forwarded to all other contracting states in the context of Annex 8, Part II, Chapter 4, Para 4.2.1. Hence, in our view, steps should have been introduced by FAA Airworthiness Directives (AD) to reduce retrospectively the flammability levels for all in-service Boeing 737s and 747s - not just the ones on the US Register.

The ASG would be interested to learn whether ICAO has any sympathy with this view. The European Aviation Safety Agency has already been informed about our view and is currently considering the possibility of retrospective action to reduce fuel tank flammability.

Thank you for your attention.

Yours faithfully

Captain Russ Williams FRAeS
Chairman, Air Safety Group

Cc EASA, NTSB, FAA, CAA

* The ASG comments on the Fuel Tank Flammability NPRM can be found on FAA Docket 2005-22997.