26 June 2009
This Service Difficulty Advisory (SDA) advises owners and operators of Transport Category Airplanes equipped with carbon brakes, utilizing airports where runway de-icing (RDI) fluids are used, that b rake failure or degradation may occur as a result of the switch to more environmental friendly organic salt RDI fluids (mainly potassium formate and acetate, but other alkalis as well
The RDI fluid remains on the underside of the aircraft and can collect as ice and slush on the landing gear, and coat the carbon brake rotors and stators . During landing gear retraction, the ice and slush on the gear (now in a horizontal position) melt on the brake units where it is further absorbed into the carbon rotors and stators.
The presence of the alkalis in the RDI creates a catalytic condition, which lowers the temperature of oxidation and softens the carbon. This condition causes the brake to flake and crumble over time, reducing the life and long-term efficiency of the brakes themselves.
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) or excessive vibration during any ground operation. It should be noted that the center of the brake unit cannot be easily inspected, and this is where its stator couplings are indexed to the torque tube, mechanically linked to the axle, thus transmitting the braking torque to the wheels.
The current Society of Automotive Engineers (SAE) Aerospace Material Specification (AMS) runway de-icer specifications were developed with the endorsement of the SAE G-12 aviation industry representatives, which included both domestic and foreign airlines, airframe manufacturers, and regulators. Modification of the SAE AMS specifications will occur once the affected parties formalize new testing protocol that has been formally endorsed by the SAE G-12, Aircraft Ground Deicing Committee.
Transport Canada recommends owners/operators of transport category airplanes equipped with carbon brakes that operate to/from airports where runway de-icing (RDI) fluids are used, to carry out a detailed visual inspection during each landing gear wheel removal, of the carbon brake rotors and stators for obvious damage, distortion, carbon chips, crushed, flaked, soft, fractured carbon or missing carbon elements . Carbon oxidation often develops on the inner diameter of the carbon stator drive lugs . Unless stator drive lugs are fractured, oxidation damage to the lugs cannot be easily detected on an installed brake.
- EASA Safety Information Bulletin No. 2008-19R1, issued January 12 2009, which can be found at: http://www.easa.eu.int/ws_prod/c/c_sin.php.
- FAA SAIB NM-08-27R1
Defects, malfunctions and failures occurring on any aeronautical product should be reported to Transport Canada, Continuing Airworthiness in accordance with the CAR 591 mandatory Service Difficulty Reporting requirements.
For further information, contact a Transport Canada Centre, or call Jean Grenier, Continuing Airworthiness, Ottawa. Telephone 613-952-4343, or facsimile 613-996-9178, or e-mail firstname.lastname@example.org.
For Director, National Aircraft Certification
Acting Chief, Continuing Airworthiness