Improved de-icing training and awareness of the impact of de-icing fluid on aircraft brakes on could help prolong the life of brakes and save the airline industry millions, according to World Aero, a multi-release EASA, FAA and TCCA certified repair station located in England which specialises in wheel and brake MRO.
Many of the brakes which come to World Aero for maintenance and repair each year have been destroyed by damage caused by de-icing fluid, according to the company.
The worst type of fluid in terms of causing brake damage is composed of an alkali-metal-salt mixture, according to Phil Randell, World Aero's managing director. This fluid is applied by airports to runways and can get transferred on to an aircraft's wheels and brakes when the aircraft is taxiing, taking off and landing.
Unfortunately no practical measures can be taken to avoid this damage caused by runway fluids, but if aircraft de-icing application methods are carried out correctly, then the damage can be minimised as far as possible, Randell says.
The contamination of aircraft carbon brakes by modern types of de-icing fluid can lead to oxidation of the brake discs, causing serious damage to brakes’ wear components.
Discovery of an oxidised brake, seen by line maintenance technicians during routine wheel changes, means the brake must then be removed from the aircraft altogether. Premature removal has costly implications for the operator, as well as an aircraft-on-ground risk, according to World Aero.
The company has seen a number of brakes where high remaining wear is left on the heat sink, but the oxidation of the discs is severe and the only option is to replace the carbon heat sink, says Randell.
Brake oxidation caused by de-icing fluid is a particular issue in countries affected by extreme, prolonged cold weather, where the use of de-icing fluid is more prevalent.
“The issue is particularly prevalent in Boeing 747-400 carbon brakes and World Aero has seen a large number of these prematurely removed from the aircraft and later scrapped due to oxidation,” says Randell. “This costs the airlines a considerable amount, with the replacement heat sink exchange ranging from $30,000 to $50,000 depending on the agreement in place with the OEM, as well as the cost of the premature removal and workshop costs.”
Says Randell: “This often makes the difference between [brakes being] repairable and non-repairable on older-generation aircraft due to the current market value of the brake. In addition to this, OEMs must scrap the removed heat sink due to oxidation, causing there to be no acceptable core heat sink, further adding to the replacement cost.”
Randell adds: “The issue can also be more prevalent in aircraft fitted with brake fans, including the BAe 146 and A320, due to de-icing fluid being sprayed and drawn into and across the brakes during turnaround. Fortunately newer aircraft avoid complications as a more advanced type of carbon is used in the brakes, which can better withstand the destructive effects of de-icing fluid.”
Notes Randell: “[Boeing] 767-300 aircraft used to be badly affected. However, Honeywell released a new carbon heat sink with improved carbon elements. Of the 50-60 Messier-Bugatti-Dowty brakes we see annually, only a very small number of brakes have been removed prematurely due to oxidation.”
The de-icing process ensures aircraft are free of ice, snow or frost before take-off. The one-step or two-step procedure involves the application of one or two types of fluid to an aircraft's flight surfaces by hose from a de-icing vehicle.
De-icing is a time-sensitive task, with operatives regularly feeling under pressure to get the job completed quickly so that the aircraft can get back in the air as soon as possible after application, according to Randell, who formerly was a line maintenance engineer at London City Airport. Part of his job consisted of approving aircraft as being airworthy to fly after de-icing.
In addition to the time pressures involved in de-icing, communication can be difficult. De-icing operatives wear ear defenders and often carry out the task in the early hours of the morning.
Furthermore, particular fluids must be reapplied if a certain time has lapsed before the aircraft has taken off. This means that if there is a long line of aircraft awaiting take-off, the process must be repeated for many aircraft, increasing the exposure of wheels and brakes to the harmful fluid.
Having had considerable experience with the de-icing process, Randell says the process is difficult and operatives face the temptation to over-apply aircraft with fluid in order to ensure that their de-icing is effective.
“The process involves covering the aircraft with de-icing fluid in order to minimise the risk of missed areas, meaning that wheels and brakes are often sprayed directly rather than avoided as they should be,” Randell points out.
However, simple improvements to de-icing training could create awareness of correct work practices and highlight the costly implications of the procedure being carried out incorrectly, according to Randell.
“De-icing training often concentrates on the importance on covering the aircraft with de-icing fluid in order to ensure effectiveness,” he says. “But when de-icing [is being performed] by hand, training could be improved to give further awareness to the airport operatives carrying out the procedure, to highlight protecting the more sensitive parts of the aircraft such as the pitot heads, equipment cooling inlets, and engine inlets, as well as of course the wheels and brakes.”
Because most aircraft wheels and brakes are under the aircraft's body or wing, they have a level of protection. So if they are not directly sprayed with de-icing fluid, damage can be avoided, with a minimal amount of drip down to the wheels to be expected, according to Randell.
Checking for damaged brakes is performed when removing the wheels for tire changes. At that point the brakes can be checked to look for crumbling of their carbon components, especially of the pressure plate located closest to the pistons: this indicates oxidisation of the heat sink.
“With improved de-ice training and awareness of the effects of de-ice fluid on brakes, operators would be able to save significant sums over the lifecycle of an aircraft by having fewer, faster and more cost-effective repairs, ensuring a longer life for brakes and avoiding expensive replacement parts,” says Randell.
Established in 1999 and located in Ditchling Common, West Sussex, World Aero provides aircraft wheel and brake component repair, overhaul, parts sales, parts exchange and inventory management for aircraft ranging from large commercial aircraft to corporate jets.