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.
It says that damage to the brakes could also lead to excessive vibration on the ground. But the FAA, which points out that a working group has been assessing catalytic oxidation of carbon brakes for the past two years, adds that the concern does not warrant an airworthiness directive.
The European Aviation Safety Agency (EASA) states: “Loss of one brake during a rejected take-off operation is potentially catastrophic, even if no accident of this kind has occurred since the introduction of environmentally-friendly de-icing fluids.”
EASA says it currently does not have jurisdiction over airport equipment, although it will gain this responsibility during a future expansion of its regulatory regime. It says that a safety regulation “could be considered, if necessary” at that point.
In the meantime it is echoing the FAA’s advisory and recommending that operators perform a visual inspection of the relevant brake components during scheduled landing-gear maintenance.
Source: flightglobal.com's sister premium news site Air Transport Intelligence news
Source: Flight International
