Reader Feedback

I received my new October issue of Aviation Maintenance, and in the first few minutes I am figuratively reaching for pen and paper. Page three, the Editor's Notebook, prompted a quick look at the FAA's brilliant website, to search for FSAW 05-08A. Then to page six, Feedback and the "Support for Fuel Tank Inerting" letter. So what's the connection? Before answering that, some reflections
on some major cock-ups that have resulted from the most laudable environmental
or safety considerations.

1: Forty odd years ago, new super-additive crankcase oils that would last forever were introduced for ship's engines. Great food for marine bacteria, which previously had to make do on nibbling at simple straight oils. Ten tonnes of bacteria in your crankcase can cause a lot of fouling, spoilage, and corrosion. Dear Lord, protect
me from anyone who wants to put exotic additive packages in aviation fuel.

2: We can't get much more environmentally friendly than building double-hull crude-oil tankers. But someone forgot that these would be giant floating thermos flasks, in which the hot cargo remained hot, and that the heat-loving type of sulphate-reducing bacteria (SRB) lurking in hot, sour oil reservoirs would flourish
on their first cruise instead of freezing to death in single-hull tankers. And they
would eat their favourite diet, ship's hull plate. I hope that there is no one out there dreaming of double-skinned aircraft fuel tanks.

3: Even worse and more pertinent to the aviation industry, new regulations a few years ago prevented ships discharging bilge water within three miles of the shore. In-shore vessels, particularly tugs, couldn't pump it out so it remained on board
until it could be off-loaded by a dockside contractor. So onboard it became
stagnant, oxygen-deficient, and smelly--and another ideal home for the savagely corrosive and oxygen-hating SRB. They rapidly drilled holes in hull bottom plate, in one case, through 11 millimeters in a year.

So what's the connection with aviation? FSAW 05-08A alerts airlines to the dramatic operational incidents caused by microbes growing in fuel in wing tanks. Actually, much more information is in IATA's Guidance Material on Microbiological Contamination in Aircraft Fuel Tanks, first published in 2000. Some microbes like eating aviation fuel, using the plentiful oxygen dissolved in it. They cause fouling and produce corrosive organic acids, amongst other things. They are pale warriors compared to the oxygen-hating sulphate-reducing bacteria. If SRB could read Feedback they would be celebrating. Removing oxygen by inerting fuel tanks? A dream come true.

So please, let's make sure that we know all the consequences before we endorse inerting. And if inerting could change the microbial flora in fuel tanks to an even more troublesome and corrosive one, let's make sure we have developed maintenance programmes for early detection and treatment. A little prior research and risk assessment would not be amiss.

E. C. Hill

Managing Director

ECHA Microbiology Ltd.

Cardiff, Wales

See www.faa.gov/library/manuals/examiners_inspectors/8300/fsaw/media/fsaw0508a.doc for the FAA flight standards airworthiness bulletin FSAW 05-08A.