Improved de-icing
training and awareness of the impact of de-ice fluid
could help prolong the life of aircraft brakes and
save the airline industry millions, says industry
specialist Phil Randell, Managing Director of World
Aero, experts in aircraft wheel and brakes.
World Aero sees many
brakes come through its EASA/FAA Part-145 certified
repair station each year destroyed by de-icing fluid
damage. The damage mainly caused by de-icing fluid
is from the alkali-metal-salt fluid applied by
airports to the runways, which can get transferred
on to the wheels (and therefore 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. 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 the wear
components. Discovery of an oxidised brake, seen by
line maintenance technicians during routine wheel
changes, mean the brake must then be removed from
the aircraft altogether, with premature removal
having costly implications for the operator, as well
as an AOG risk. World Aero has seen a number of
brakes where high remaining wear is left on the heat
sink, but the oxidation is severe and the only
option is to replace the carbon heat sink. It is of
course a particular issue in countries affected by
extreme, prolonged cold weather where the use of
de-icing fluid is more prevalent.
The vital process
of de-icing ensures that aircraft are free of ice,
snow or frost before take-off.
The one
or two-step procedure involves the
application of one or two types of fluid
to the aircraft surfaces by hose from a
de-icing vehicle. It 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. In addition to this,
communication can be difficult, with
operatives wearing ear defenders and
often carrying out the task in the early
hours of the morning. Furthermore,
particular fluids must be reapplied if a
certain time has lapsed before the pilot
has taken off, meaning if there is a
long queue for take-off the process must
be repeated, increasing the exposure of
wheels and brakes to the harmful fluid. |
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Heavily
oxidised B747 brake. |
Having previously
worked at London City Airport as a Line Maintenance
Engineer certifying aircraft as ready for flight
after de-icing, Phil Randell knows first-hand the
difficulty of the process and the temptation to
over-apply aircraft with fluid in order to ensure
that 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.”
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Phil
Randell explains:
“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.
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.
This often makes the difference between
repairable and non-repairable on the
older generation aircraft due to the
current market value of the brake. |
Typical
as-removed B747 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.
“The issue can
also be more prevalent in aircraft fitted with brake
fans, including BAe146 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,” Phil goes on. “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.”
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, Phil Randell advises.
“De-icing training often concentrates on the
importance on covering the aircraft with de-icing
fluid in order to ensure effectiveness,” says Phil,
“but when de-icing 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.”
As most aircraft
wheels and brakes are under the body or wing, they
have a level of protection, so if not sprayed
directly, damage can be avoided, with a minimal
amount of drip down to the wheels to be expected.
Checking for damaged brakes is done when removing
the wheels for tyre change, when a check on the
brakes can be performed to observe for crumbling of
the carbon components, especially of the pressure
plate located closest to the pistons, which
indicates oxidisation of the heat sink.
“With improved
de-ice training and awareness of the effects of
de-ice fluid on brakes,” Phil concludes, “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.”
Established in
1999, World Aero are experts in aircraft wheels and
brakes, providing aircraft wheel and brake component
repair, overhaul, parts sales, parts exchange and
inventory management for international aviation
customers; from commercial airline fleets to
corporate jets. World Aero is a multi- release EASA,
FAA and additionally TCCA certified repair station.
www.worldaero.co.uk |