Hot Brakes & Wheel Assemblies

Randy KrausePort of Seattle Fire Department

Fire ChiefOctober 2010

“To Promote the Science and Improve the Methods of Aviation Fire Protection and Prevention”

Dash 80 Video1954

Command Post Video1973

747-400 ER Video2002

787 Brake Test 2010

OBJECTIVES

• Causes of Hot Brakes• Hazards• 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.

Hazards• 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 aft

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.

• 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.

Michelin Recommended Approach

Tire Burst

NFPA 402 Recommendation

12.4 Hot Brakes and Wheel Fires.

12.4.2 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.

12.4.4 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.

12.4.5 Foam, water spray, halogenated agent, and dry chemical are effective agents for direct application on brake fires.

12.4.6 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.

12.4.7 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.

12.4.8 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 distinguishbetween 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

BUCKEYE FIRE EQUIPMENT COMPANY

• Use of ABC Dry Chemical Fire Extinguishers on Aircraft Fires

• The basic component of the extinguishing agent contained in an ABC fire extinguisher is mono-ammonium 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 aircraft.

Boeing Dry Chem Recommendation

SUGGESTED OPERATOR ACTION:Boeing recommends that operators and airplane maintenance providers take positive actions toprevent the use of dry chemical fire extinguishes in and around airplanes. This action shouldinclude 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 beadvised through formal training programs or other appropriate means on the potential damagethat can be caused by the use of dry chemical fire extinguishers on airplane fires. Steps should betaken to replace dry chemical extinguishers that are located near parked airplanes and installed onairplane ground service equipment. The dry chemical extinguishers should be replaced asappropriate with suitably rated water, carbon dioxide, aqueous film-forming foam (AFFF), andHalon or Halon replacement type fire extinguishers.

If a dry chemical extinguisher is used on an airplane, the airline should contact their assignedBoeing Field Service Representative for specific advice and information regarding the removal ofdry 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

reach

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-7-3.1All-purpose (ABC) dry chemical-type extinguishers should not be used in situations where aluminum corrosion is a problem.

NFPA Fire Protection Handbook Chapter-Basics of Fire and ScienceExtinguishment 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."

WaterWhen 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

Questions?

“To Promote the Science and Improve the Methodsof Aviation Fire Protection and Prevention”