Damaged right landing gear assembly of a DA40 after an extended taxi with a strong quartering tailwind

What can you do?  You have just been cleared to taxi… to the far end of the field.  That could be 1 mile away, or it could be more.  We have all faced this situation.  We may have actually done it a hundred times and never thought about the possibility of how hard our brakes are working and what could happen if they worked too hard.

The fact is that our brakes on our DA20, DA40, DA42, and for that matter every aircraft are designed to slow down our aircraft after landing, but the energy of stopping the aircraft must be converted into another form.  The brakes convert that energy into heat which must be dissipated somehow.  This is not a new concept.  Aircraft and any other vehicle installed with brakes must somehow shed the heat generated after use.  In fact, that heat, measured in temperature, continues to rise for sometime after the brakes have been released actually peaking up to almost a minute after the brakes have been released.  A protracted taxi with power and brake is like driving your car with one foot on the gas and the other on the brake.  Not only is there risk of overheating or even fire, there is also the very real possibility of brake fade, rendering them useless when you need them most.  Any brakes should be used intermittently, not continuously.   

Why is this situation of any more concern on Diamond aircraft than any other aircraft that we have been flying since the 1970s?  The fact is that our aircraft have castering nose wheels and main wheels enclosed by aerodynamic wheel fairings which can retain heat generated by braking.  In order to steer, we must use a combination of rudder and brake to get the aircraft to go where we want.  Most of us have mastered that concept and found that a castering nose wheel gives us amazing control over maneuvering on the ground (except for pushing the aircraft backwards into a parking space).

Is there a time when pilots have to exercise a different amount of discretion over the use of brakes during taxi operations?  The answer is yes, especially anytime we have a quartering wind.

Case in point:  A DA40 was recently cleared to taxi to the opposite end of the parallel runway at a Midwest airport due to a temporary closure of the closer runway.  The pilot began the taxi and upon turning down the 1.3 mile stretch of the parallel taxiway, they started to feel the effects of the 12 knot left quartering tailwind.  That wind was pushing on the back of the aircraft scooting it along, but also it was trying to weathervane the tail to the right, requiring the pilot to keep pushing hard on the right rudder to pull it back to the taxiway centerline.  This required the pilot to advance some power to energize the rudder with some control authority.  In order to do this and to keep the aircraft from squawking low voltage alerts and cautions to the pilot, the power was advanced to about 950 RPM.  Now the aircraft would have been taxiing too fast for the conditions.  The pilot naturally started using the right brake to help keep the aircraft on the taxi centerline stripe.  When the pilot reached the end of the taxiway, he noted a strange burning smell.  He did not have to wait long before the aircraft behind him announced to the tower that the DA40 had smoke pouring out from under the right wing.  The tower urgently prompted the pilot to evacuate the aircraft and called the fire department.

The aircraft's right wheel had now burst into flames while the pilot sat and watched in horror as the aircraft wing burned.  The rescue crew arrived quickly and started dousing the right wing with “Purple-K” chemical extinguishing agent.  After 5 minutes, it was over.  The wheel brake had done its job and converted that energy to heat.  That heat, contained within the efficiently designed wheel pant had transferred through the brake rotor to the tire.  The tire burned and set the wheel pant on fire.  Once the wheel pant burned, it started burning the underside of the wing with a nasty burn mark between the forward and the aft spar.  The Purple-K of the crash rescue team did its job, but the cabin is now coated with the agent because the pilot left the canopy open in his haste to evacuate the aircraft.  The pilot was lucky.  He could have started down the runway for takeoff and then found out, complicating the resulting outcome in some unimaginable way.  The aircraft was not so lucky.  It will not be flyable for months while the wing, flap, and entire landing gear assembly is replaced.

Post fire remains of the wheel, tire, and fiberglass fairing of a DA40

What can we learn from this situation and how can we avoid having it happen to other unsuspecting pilots of sleekly designed aircraft?  First, this could have happened on any aircraft, but it tends to be more pronounced on castering nose steering aircraft with aerodynamically designed main wheel fairings such as Diamond, Cirrus and Columbia.  Second, we need to be aware of what the wind is doing to our aircraft at all times and have a plan for action.  Our instructors have always taught us to use aileron correction for quartering headwinds and tailwinds, but have they ever provided us information about brake duty cycle?  Is there even anything in the Aircraft Operations Manual about this? Probably not to either question.

There was little that the pilot could have done differently that day, but here are a few tips that might make a difference the next time.  First, slow down the taxi by pulling back the power.  Make sure that the rudder is being used fully for steering before the brakes are called to action.  Pause along the long taxi distance at the midpoint to allow the brakes to cool, if you suspect that you are using excessive brakes to keep the aircraft straight during the taxi.

I can assure you that a brake fire was the last thing on this pilots mind.  Diamond reports that this is the first such situation of a brake fire that has been reported during taxi, although there was another situation where an aircraft was towed with the parking brakes set which resulted in a fire.  Cirrus Aircraft went through a rash of brake fires in the past year, so Diamond owners should not feel slighted.  This is not the last time this will happen, either.  We can only communicate the situation to other pilots who, now armed with the unfortunate outcome, can store yet another piece of operational data in their already loaded brains.  This is aviation.  That is our job.