DCA11FA072

The flight crew stated that while on final approach, they noted a right engine 10th stage bleed air indication, a right jet pipe over-heat indication, and a right pack over pressure indication. They also noted, after landing, that there was a burning smell. Postaccident examination of the airplane revealed fire damage to the aft equipment bay in the area of the right pylon directly above the auxiliary power unit (APU) exhaust duct. There was evidence of chaffing on the right integrated drive generator (IDG) power feeder cable as well as damage to an adjacent hydraulic line. Additionally, two support brackets, designed to secure the hydraulic line to the aft fuselage, near the area of the fire had fractured, with one bracket no longer attached to the fuselage. Consistent with the chafing, there was a pin-sized hole near the end of the hydraulic line where it connected to a fitting that was mounted on a bracket attaching the line to the airplane's structure. The pin-sized hole was near the chafed IDG cable strand, and about 0.0625 inches from the hydraulic line, instead of the required minimum distance of 2.0 inches specified in Bombardier wiring installation specifications. NTSB Metallurgical examinations of the IDG power feeder cable revealed that the damage to the insulation around the pin-sized hole was consistent with chafing. The examination also found material splatter consistent with electrical arcing of the conductors. The damaged area of the hydraulic line revealed evidence of splattering and material expulsion consistent with electrical arcing against the hydraulic line's external surface. Additionally, the chaffed wire and hydraulic line were examined using energy dispersive x-ray spectroscopy (EDS) to determine if any material transfer consistent with an electrical arcing event, had occurred and the wire and the hydraulic line both had chemical elements not normally found in each. The bracket had fractured into two pieces, and one of the tabs matched the fracture on the main body of the bracket. There was fretting wear damage on the surface of the tab where it was attached to another surface indicative of the tab possibly having rubbed against a bolt or pin used to mount the bracket, and the fracture surface exhibited dimpled ductile fracture that is indicative of overstress bending. As a result of the findings from this accident, both Transport Canada and the FAA released Airworthiness Directives.

On April 2, 2011, about 0900 central daylight time, Mesa Airlines flight 2651, a Bombardier CL-600-2B19, N7264, experienced an inflight fire while on approach to Phoenix Sky Harbor International Airport (PHX), Phoenix, Arizona. There were no injuries to the 49 passengers and crew onboard but the airplane was substantially damaged. The flight was operating under the provisions of 14 Code of Federal Regulations Part 121, as a regularly scheduled domestic passenger flight from Des Moines International Airport (DSM), Des Moines, Iowa. According to the flight crew, while on final approach to Phoenix Sky Harbor International Airport, they received a right engine 10th stage bleed air indication followed by a right jet pipe over-heat indication and a right pack over pressure indication. Immediately after landing, the flight crew smelled a burning smell but that it went away. There was no electronic flight instrument display or master warning indications of a fire. Postaccident examination of the airplane revealed substantial structural damage as a result of the fire to the fuselage skin, frames, and stringers as well as portions of the pylon from Fuselage Station 640 to about 700. Inspection of the fire damaged area revealed evidence of chaffing on the right integrated drive generator (IDG) power feeder cable and damage to an adjacent hydraulic line. The chafing occurred in the area where the cable was routed adjacent to a pressurized hydraulic line from the right engine driven pump. The hydraulic line contained a pin-sized hole located in the area near the chafed IDG cable strand. The distance between the hydraulic line and the cable was measured and found to be 0.0625 inches. According to Bombardier's wiring installation specifications, electrical wiring should be separated 2.0 inches from flammable liquids and/or gas lines, such that any deflection of the wiring cannot result in a clearance of less than 0.5 inches. Further examination revealed that the two hydraulic line support brackets in the area of the fire had fractured, with one bracket no longer attached to the fuselage. The damaged IDG wire bundle, hydraulic tubing, and support brackets were examined at the NTSB Materials Laboratory. Damage to the IDG wire insulation was consistent with rubbing/chaffing and damage to the conductors was consistent with electrical arcing. Damage to the stainless steel hydraulic line was consistent with electrical arcing against the hydraulic line's external surface. Additionally, the bracket had fractured into two pieces, and one of the tabs matched the fracture on the main body of the bracket. With the associated tab there was fretting wear damage on the surface of the tab where it was attached to another surface indicative of the tab possibly having rubbed against a bolt or pin used to mount the bracket. The fracture surface exhibited dimpled ductile fractures consistent with an overstress bending fracture. Because of this accident, on June 29, 2011,Bombardier issued a service letter recommending that operators perform a detailed visual inspection in the affected area at the earliest possible convenience. The inspection called for operators to pay particular attention to low clearances between the right-hand engine IDG power cables, hydraulic lines, and the support brackets for each. It also went on to provide inspection criteria for said inspections. On July 7, and August 25, 2011, Transport Canada and the FAA respectively released Airworthiness Directives (AD) each, calling for a check for chafed or damaged IDG power cables, and hydraulic lines, and for cracked or broken hydraulic line support brackets in the affected area. The FAA's version of the AD went on to say that "Chafed IDG power cables can generate high energy arcing that can result in an uncontrolled fire in the aft equipment bay."