Mesa CRJ2 at Phoenix on Apr 2nd 2011, burning odour, multiple master cautions and warnings on final approach
Last Update: April 9, 2020 / 11:58:12 GMT/Zulu time
The aircraft left Mesa Airlines' fleet on that day and was scrapped in January 2012.
On Jun 17th 2015 the NTSB released a preliminary note stating, that an investigation into the occurrence rated an accident has been opened. The NTSB reported that a post occurrence investigation revealed substantial damage to the right hand pylon in the aft equipment bay area directly above the APU exhaust duct.
On Apr 8th 2020 the NTSB released their final report concluding the probable cause (adopted Apr 6th 2020) was:
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.
The NTSB reported:
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.
Aircraft Registration Data
This article is published under license from Avherald.com. © of text by Avherald.com.
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