Bombardier CL600 2B19 N7264V accident near Phoenix, Arizona

Probable cause

inadequate clearance between the Integrated Drive Generator (IDG) power cables and hydraulic lines in the aft equipment bay that resulted in chaffing of the IDG power cables and hydraulic lines, arcing, and fire.

NTSB analysis

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.

Text from the NTSB. Open the NTSB docket for DCA11FA072 for the full record.