WARNING Do not stand directly in front of the intake duct. HOT BRAKES During   a   normal   or   an   emergency   landing,   the landing gear is an item of considerable concern.   With the    added    weight    and    landing    speeds    of    modern aircraft, and because of the extreme braking required on shorter  runways,  overheated  brakes  and  wheels  are  a common occurrence.  You, as a fire fighter, must have a thorough   understanding   of   the   hazards   created   by overheated   brakes,   as   well   as   the   techniques   and equipment used with this type of emergency. Overheated   aircraft   wheels   and   tires   present   a potential   explosion   hazard   because   of   built-up   air pressure in the tires, which is greatly increased when fire   is   present. To   avoid   endangering   the   crews needlessly, all nonessential personnel should evacuate the   area.   The   recommended   procedure   for   cooling overheated wheel, brake, and tire assemblies is to park the aircraft in an isolated area and allow the assemblies to  cool  in  the  surrounding  air.  Using  cooling  agents, such  as  water,  is  not  recommended  unless  absolutely necessary  due  to  increased  hazards  to  personnel  near the    overheated    assembly.    Most    aircraft    operating manuals  for  propeller-driven  aircraft  recommend  that flight crews keep the propeller turning fast enough to provide  an  ample  cooling  airflow. Most  major  jet, propeller-driven,    and    turboprop    aircraft    now    have fusible  plugs  incorporated  in  the  wheel  rims.    These fusible plugs are designed to automatically deflate the tires.   (Failure of fusible plugs to function properly has occurred.) Releasing   the   tire   pressure   reduces   the pressure    on    the    wheel,    and    thus    eliminates    the possibility of explosion. CAUTION The  use  of  CO₂  for  rapid  cooling  of  a  hot brake or wheel assembly is extremely dangerous. Explosive fracture may result because of the rapid change in temperature. When responding to a wheel fire or hot brakes as a member of the emergency crew, you should approach the wheel with extreme caution in a fore or aft direction, never   from   the   side   in   line   with   the   axle. Peak temperatures may not be reached until 15 to 20 minutes after  the  aircraft  has  come  to  a  complete  stop.  See figure 12-15. WHEEL ASSEMBLY FIRES The following types of fires and hazards may occur around an aircraft wheel assembly: 1. The    heating    of    aircraft    wheels    and    tires presents a potential explosion hazard, which is greatly increased  when  fire  is  present.     The  combination  of increased     stress     on     the     brake     wheel     assembly, additional    tire    pressure,    and    the    deterioration    of components  by  heat  may  cause  an  explosion. This explosion  is  likely  to  propel  pieces  of  the  tire  and/or metal through the air at high speeds. 2. Materials that may contribute to wheel assembly   fires   are   grease,   hydraulic   fluid,   bearing lubricants, and tire rubber. a. Grease and bearing lubricant fires.   When ignited,  wheel  grease  fires  can  be  identified  by  long flames around the wheel brake/axle assembly.    These fires   are   usually   small   and   should   be   extinguished quickly with Halon 1211 or water fog. b. Rubber  tires.    Rubber  from  the  tires  may ignite  at  temperatures  from  500°F  (260°C)  to  600°F (315°C)  and  can  develop  into  an  extremely  hot  and destructive  fire.    Halon  1211  or  water  fog  should  be used    as    early    as    possible    to    extinguish    the    fire. Reignition    may    occur    if    the    rubber    sustains    its autoignition temperature or if the rubber is abraded and the fire is deep-seated. c. A broken hydraulic line may result in the misting  of  petroleum-based  fluids  onto  a  damaged  or 12-20 Figure  12-15.—Danger  zones  and  attack  zones  in  combating wheel  fires. (Attack  the  fire  from  fore  and  aft—do  not attack from the side).