N617FB

On May 17, 2012, about 0715 central daylight time, a Shorts SD3-60, N617FB, registered to ACC Integrated Services Inc., of Milwaukee, Wisconsin, was substantially damaged following a wheel brake fire during taxi at the George Bush Intercontinental Airport, Houston, Texas. The airline transport pilot and commercial co-pilot were not injured. The airplane was being operated by Air Cargo Carriers LLC of Milwaukee, Wisconsin, as an air cargo flight under the provisions of 14 Code of Regulations Part 135. Visual meteorological conditions prevailed and a flight plan was filed. The airplane was taxiing to position for takeoff from runway 8R and its intended destination was Austin, Texas.

The flight crew reported that the airplane was about 60 pounds over its maximum weight for takeoff. Since their taxi to the assigned runway was long, they decided to reduce weight by using higher-than-normal engine power settings while maintaining some amount of braking to control speed while taxiing in order to burn fuel prior to takeoff. During the taxi, the right and left main landing gear tires deflated when the fusible plugs in the wheels blew out due to over-heating, and a fire ignited in the right wheel housing. The crew reported that they felt the airplane yaw as the tires deflated and were informed via radio by a following airplane that their right wheel was on fire. The crew brought the airplane to a stop on the taxiway, evacuated, and attempted to extinguish the fire with two hand-held fire extinguishers.

Airport fire fighting personnel arrived on scene and extinguished the fire using foam suppressant. The fire resulted in substantial damage to the wing support structures. No injuries were incurred to the flight crew or ground personnel. Although the fire damage was extensive, postaccident examination of the airplane by an FAA inspector, a NTSB investigator, and the operator's maintenance personnel did not show evidence of mechanical malfunction or abnormalities with the wheel and brake system.

The Shorts SD3-60 is a twin turbo-prop, strutted, high-wing airplane. Each of the main wheels are equipped with fusible plugs that are designed to blow out in the event of severe wheel overheating. Inspection of the airplane's wheel and brake systems after the accident showed that the plugs on both main wheels blew out as designed. The fire caused severe damage to the right main gear housing, which was part of the stub wing assembly structure and incorporates the attachment fitting for the wing strut. The operator's maintenance department believed that the fire caused substantial structural damage to the extent that repair was not practical.

The operator submitted in NTSB Form 6120 that both crew members stated that they had been trained to not ride the brakes while taxiing. Additionally, the Captain stated that he did not realize that he was in danger of blowing the tires much less causing a fire, otherwise he would not have attempted to bum off excess fuel while taxiing. The operator revised its training program to highlight the hazards of excessive brake use during all ground operations, including taxi. Additional emphasis will be placed on the purpose of the fusible plugs and photographs of the event will be used in all future training classes where the brake system is taught.