Hot Brakes & Wheel Assemblies
“To Promote the Science and Improve the Methods
of Aviation Fire Protection and Prevention”
Randy Krause
Port of Seattle Fire Department
Fire Chief
October 2010
Dash 80 Video
Command Post Video
747-400 ER Video
787 Brake Test 2010
Causes of Hot Brakes
Extinguishing agents
Approaching the aircraft?
New Technologies (The “science”)
Causes of Hot Brakes
• Aircraft weight –
– Landing with excess weight (extra fuel)
– To short of runway for the aircraft weight and size
• Landing speeds
– Reverser malfunction
– Short runway
• Extraordinary braking
– Short runway
– Reverser malfunction
• Refused take - off (RTO)
New Technology
What is the wheel assembly/brakes made of?
• Cera-metallic
• Aluminum alloy
• Carbon
• Composite
Note: Today magnesium and titanium are not
being used in the commercial aircraft
wheel assemblies or braking systems.
• Tire failure
– Blow out due to age or other factors such as FOD, over inflation, or
it just wears out. (where does tire fail)
• Fusible plugs
– Failing to operate as designed
• Disintegration of wheel assembly
– Explosive fragmentation due to tire failure or rapid cooling
• Has anyone witnessed this? If so, why did it happen?
• Danger zone ( Approx. 300 feet )
– Outside of a 45 degree angle from gear truck centers forward and
Approaching the Aircraft
• Establish communication with pilot
– Let the flight deck know by radio who you are, what the problem is,
where you currently are, and where you want to go
• Approach from front or aft or 45° angle?
– New approach or “old” school?
• Type of aircraft
– Lower wing aircraft and or engine placement may interfere with
proper ARFF placement
– Heavier aircraft = more gear trucks, wheels and brake assemblies
• Observe tire condition
– Are they inflated, deflated, appear larger than others or on fire
• Is there smoke or fire ?
Boeing Recommendation
Approach Main Gear Along Arrows Never Enter Shaded Areas
When There Is A Suspect Hot Brake Or Tire. Stay At Least 25
Feet (7.6 meters) Away From Tire Or Rim Until Temperature
Returns to Ambient.
Michelin Recommended Approach
In service, tires should also be treated with care so as to avoid conditions
that would damage the tire and wheel assembly or create a dangerous
situation for those around the assembly or aircraft.
You should never approach, or allow anyone else to approach, a tire and
wheel assembly mounted on an aircraft that has obvious damage until that
assembly has been allowed to cool to ambient temperature. This cooling
generally requires at least three hours.
Always approach a tire and wheel assembly from an oblique angle, in the
direction of the tire’s shoulder.
Tire Burst
NFPA 402 Recommendation
Hot Brakes and Wheel Fires.
In order to avoid endangering ARFF personnel and aircraft occupants and causing unnecessary damage
to the aircraft, it is important not to mistake hot brakes of brake fire. Hot Brakes normally cool by
themselves and do not require an extinguishing agent.
ARFF personnel should remain clear of the sides of the aircraft wheel assemblies that are involved in fire
and approach only in a fore and aft direction. Since heat is transferred from the brake to the wheel,
extinguishing agent should be applied to the brake area. The primary objective is to prevent the fire from
spreading upward into the wheel wells, wings, and fuselage.
Foam, water spray, halogenated agent, and dry chemical are effective agents for direct application on brake fires.
Dry Chemical agents and halogenated agents might extinguish fires involving hydraulic fluids and lubricants,
but re-ignition can occur since these agents lack sufficient cooling effect. Halogenated agents are particularly
effective in extinguishing undercarriage fires; however, where magnesium wheel components are burning,
halogenated agents should not be used.
Effectiveness of any gaseous extinguishing agent can be severely reduced if wind conditions are such that
sufficient concentration cannot be maintained to extinguish the fire.
Solid streams of water should be used only as a last resort on wheel fires since the rapid cooling can cause an
explosive failure. However, fires involving magnesium wheels have been successfully extinguished by applying
large amounts of water from a distance. This method rapidly reduces the heat to a point below the ignition
temperature of the magnesium, and the fire is extinguished,. ARFF personnel should exercise extreme caution
when this method of extinguishment is used, as explosive failure of the wheel components is likely.
5th edition; IFSTA Language pg. 342
Acceptable Methods for cooling hot brakes include the following:
Continue to Taxi – will assist in dissipating heat when appropriate; only useful if taxiing can be done without the flight
crew applying the brakes; ARFF personnel should monitor this condition until it is determined to be safe.
Normal Cooking – wheel assembly cools on its own in a remote area of the airport designated be ARFF personnel;
ARFF personnel should monitor this situation until it is determined to be safe.
Water mist of fog pattern – cools wheel assembly; water mist or fog pattern in a continuous flow is a suitable
alternative and safer than using fans in most cases.
Fans – air cools wheel assembly; suitable method to expedite normal cooling; most ARFF departments use portable
fans, and this used places firefighters close to the hazard zone.
Wheel Fires pg 343.
If the wheel assembly is on fire, the safest approach is to use large amounts of water from a distance using
turrets. This application keeps the firefighters out of the hazard zone and allows for extinguishment and rapid
cooling. Once the fire is out, cooling efforts should be maintained to minimize damage to other components.
Handlines can be used in place of turrets as long as the firefighters approach from a fore or aft position. If water is
not available, any suitable agent should be used to extinguish the wheel fire.
The use of combustible metals in the wheel assemblies is declining due to the increased weight of the metals and
their tendency to accumulate rust. New generation brake and wheel assemblies are constructed of cera-metalic,
aluminum alloy, and carbon posing less of a hazard than older generation assemblies, which contained small
amounts of magnesium or titanium in their construction. These metals are rarely found in today’s commercial and
military aircraft. These changes should be taken into consideration when addressing department policy in
handling these types of emergencies.
ICAO Language
12.2.3 Hot brakes and wheel fires.
The heating of aircraft wheels and tires presents a potential explosion hazard, greatly
increased when fire is present. In order not to endanger the members of the airport
rescue and fire fighting service needlessly, it is important to distinguish
between hot brakes and brake fires. Hot brakes will normally cool by themselves
without the use of an extinguishing agent. Most aircraft operating manuals for
propeller driven aircraft recommend that flight crew members keep the propeller
forward of the fire turning fast enough to provide an ample cooling airflow. Most
wheels of jet aircraft have fusible plugs which will melt at about 177°C and deflate the
tire before dangerous pressures are reached. When responding to a wheel fire,
airport rescue and fire fighting members should approach the wheels with extreme
caution in a fore or aft direction, never from the side in line with the axle.
“Since the heat is transferred to the wheel from the brake it is essential that the
extinguishing agent be applied to this area. If further cooling is desired after
extinguishment of the fire, the agent should be directed at the brake area only.
ICAO Language
12.2.4 Too rapid cooling of a hot wheel, especially if localized, may cause
explosive failure of the wheel (is this a true statement). Solid streams of
water should not be used except as a last resort. Water fog can be used but
intermittent application of short bursts of 5 to 10 seconds eve:y 30 seconds
is recommended.
Dry chemical has limited cooling capacity but is an effective extinguishing
agent. Once the tires are deflated, any extinguishing agent may be safely
used as there is no further danger of explosion.
Extinguishing Agents
• Dry chemical
• Dry powder
• Water
– Plentiful, available, cheap and environmentally friendly
• Foam
• Dual agent
• Use of ABC Dry Chemical Fire Extinguishers on Aircraft
The basic component of the extinguishing agent contained in an ABC fire extinguisher is monoammonium phosphate (sometimes referred to as MAP). The agent is very efficient at
extinguishing Class A type fires because it “melts” and forms a crust on the surface of the burning
material, creating an oxygen barrier. When used on an aircraft fire the agent can flow into minute
structural cracks common in the aircraft’s stressed aluminum surfaces. There it can combine with
moisture to form phosphoric acid, a chemical that is highly corrosive to aluminum. The residue is
extremely difficult to clean up and failure to completely clean the agent from the aircraft will, over
time, result in corrosion that could compromise the integrity of the aircraft. For this reason
Buckeye Fire Equipment Company does not recommend the use of ABC fire extinguishers on
Boeing Dry Chem Recommendation
Boeing recommends that operators and airplane maintenance providers take positive actions to
prevent the use of dry chemical fire extinguishes in and around airplanes. This action should
include airlines and maintenance providers coordinating with airport authorities, maintenance,
fueling service providers, ground service providers, and airport fire services. Operator personnel,
maintenance and service providers, airport authorities and airport fire service personnel should be
advised through formal training programs or other appropriate means on the potential damage
that can be caused by the use of dry chemical fire extinguishers on airplane fires. Steps should be
taken to replace dry chemical extinguishers that are located near parked airplanes and installed on
airplane ground service equipment. The dry chemical extinguishers should be replaced as
appropriate with suitably rated water, carbon dioxide, aqueous film-forming foam (AFFF), and
Halon or Halon replacement type fire extinguishers.
If a dry chemical extinguisher is used on an airplane, the airline should contact their assigned
Boeing Field Service Representative for specific advice and information regarding the removal of
dry chemical extinguishing agents from the affected area of the aircraft.
Boeing Flight Test
• Minor temperatures – Heat waves observed, minor smoke light blue
in color.
– Water or air cool
• Extreme temperatures – Glowing, open flames, moderate to heavy
dark colored smoke
– Cool with water
• If Fusible Plug fails – Open flames, heavy dark colored smoke, slag
dripping temperatures are extreme and a severe hazard exists!
– Cool with large amounts of water preferably with turrets at maximum
Can I use a dry chemical fire extinguisher rather than Halon?
The best way to answer this question is to cite NFPA Standards and other published documents:
NFPA 410 Aircraft Maintenance (Addendum) A-7-3.1
All-purpose (ABC) dry chemical-type extinguishers should not be used in situations where aluminum corrosion is a
NFPA Fire Protection Handbook Chapter-Basics of Fire and Science
Extinguishment with Dry Chemical Agents:
One reason that dry chemical agents other than monoammonium phosphate are popular has to do with corrosion. Any
chemical powder can produce some degree of corrosion or other damage, but monoammonium phosphate is acidic
and corrodes more readily than other dry chemicals, which are neutral or mildly alkaline. Furthermore, corrosion by
other dry chemicals is stopped by moderately dry atmosphere, while phosphoric acid has such a strong affinity for
water that an exceedingly dry atmosphere would be needed to stop corrosion.
Air Transport Newsletter, by Ronald Horn, Nov./Dec. 1983, "Class A-B-C Extinguishers Damage Aircraft"
"The A-B-C extinguishers have excellent fire-fighting capability, but the mono-ammonium-phosphate chemical agent
melts and flows when it comes into contact with heat. This is how it gets its Class A rating. This chemical is highly
corrosive to aluminum, and once it contacts hot aluminum and flows down into the structural cracks and crevices it
cannot be washed out as the B-C dry chemical agents can.
"Once an A-B-C extinguisher is used on an airplane, it is necessary to disassemble the aircraft piece by piece and
rivet by rivet to accomplish cleanup. Failure to do so will result in destruction of the aircraft by corrosion."
When using water:
• As much as available to prevent warping the axle.
• Use hand line / HRET / turret
– Booster reel for hot brakes
– Combat line or turret for brake fire
• Cool entire wheel and brake assembly
• Be aggressive!
– Which means be quick, and careful
“To Promote the Science and Improve the Methods
of Aviation Fire Protection and Prevention”

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