Incident Overview
On April 2, 2011, about 0900 central daylight time, Mesa Airlines flight 2651, a Bombardier CL-600-2B19 (registration N7264), experienced an inflight fire while on approach to Phoenix Sky Harbor International Airport (PHX), Phoenix, Arizona. The flight was operating under 14 CFR Part 121 as a regularly scheduled domestic passenger flight from Des Moines International Airport (DSM), Des Moines, Iowa. There were no injuries to the 49 passengers and crew members onboard, but the airplane was substantially damaged.
Flight Crew Account
According to the flight crew, while on final approach to Phoenix Sky Harbor, 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 odor, but it dissipated. There were no electronic flight instrument display or master warning indications of a fire.
Postaccident Examination
Postaccident examination revealed substantial structural damage from 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 showed evidence of chafing on the right integrated drive generator (IDG) power feeder cable and damage to an adjacent hydraulic line. The chafing occurred 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 in the area near the chafed IDG cable strand. The distance between the hydraulic line and the cable was measured to be 0.0625 inches.
Bombardier's wiring installation specifications require electrical wiring to 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.
Examination of Components
Further examination revealed that two hydraulic line support brackets in the fire area 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/chafing, 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, one bracket had fractured into two pieces, with a tab matching the fracture on the main body. The tab exhibited fretting wear damage on its surface where it attached to another surface, indicative of possible rubbing against a bolt or pin used to mount the bracket. The fracture surface showed dimpled ductile fractures consistent with an overstress bending fracture.
Corrective Actions
On June 29, 2011, Bombardier issued a service letter recommending that operators perform a detailed visual inspection of the affected area at the earliest possible convenience. The inspection focused on low clearances between the right-hand engine IDG power cables, hydraulic lines, and support brackets, and provided inspection criteria.
On July 7 and August 25, 2011, Transport Canada and the FAA respectively released Airworthiness Directives (ADs) requiring checks 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 AD stated that "Chafed IDG power cables can generate high energy arcing that can result in an uncontrolled fire in the aft equipment bay."