Wednesday, June 11, 2008

When concern for the environment brings unexpected dangers

I was intrigued to read about an unexpected side-effect of environmental consciousness. Flight reports:

US and European regulators are recommending that carriers inspect the carbon brakes of aircraft after finding that modern runway de-icing fluids, containing organic salts, can damage the carbon components and potentially lead to brake failure.

The US FAA is planning to modify runway de-icer specifications once a new formal testing protocol has been endorsed. But it is advising operators of carbon brake-equipped aircraft to carry out detailed visual inspection of carbon heat packs for signs of corrosion or other damage.

While carbon brakes have been fitted to aircraft for several years, the switch to organic-salt de-icing fluids – which are considered more beneficial to the environment – has introduced a risk to their integrity.

Aircraft operations in snow or ice can result in slush on the ground, mixed with de-icing fluid, being sprayed into the brakes and their carbon plates, particularly during take-off or landing. Gear retraction exacerbates the problem by allowing the melting slush to flow into the brake assembly.

At high temperatures, some 400-500°C, thermal oxidation can occur in the brakes. While this does not normally have an effect on brake life, alkalis in the de-icing fluid can reduce the temperature at which oxidation begins to around 100-200°C.

The higher probability of exposure to these lower temperatures means the carbon is more likely to soften and crumble over time.

“As a result there is a danger of possible brake failure during high-speed aborted take-off or dragged brake during normal take-off – and subsequent overheat once airborne,” says the FAA in an airworthiness information bulletin.

The article goes on to quote the European Aviation Safety Agency as saying that losing even one brake during a rejected take-off is 'potentially catastrophic'.

Interesting. Greater concern for the environment is a very good thing, I think - but you'd better check out all the consequences first! I wonder whether this has contributed to any accidents in recent years? I've read about several runway over-runs on landing . . . wonder if unduly and/or prematurely worn carbon brakes, caused by this stuff, had anything to do with them? And, if so, will we ever be told?



Peripatetic Engineer said...

Murphy's Law of Unintended Consequences stikes again!

Anonymous said...

I will bet we will never be told if brake failure was the reason.