Accident Overview
On March 23, 2012, at 1100 central daylight time, a Cirrus Design Corporation model SR22T airplane, N229TX, was substantially damaged during an electrical fire while taxiing for departure at Addison Airport (ADS), Addison, Texas. The commercial pilot and passenger were not injured. The airplane was operated by PlaneSmart! Aviation LLC under Part 91 without a flight plan. Day visual meteorological conditions prevailed.
Sequence of Events
The pilot reported that after a short taxi, the primary flight display (PFD) and multifunction display (MFD) suddenly lost all displayed information. The circuit breakers for battery No. 1 and alternator No. 2 had tripped and could not be reset. The pilot advised the tower controller of the intent to return to the ramp. The controller informed the pilot that the control tower was changing active runways and expected a hold of about 5 minutes. The airplane then experienced a total loss of electrical power. The pilot turned toward the tower to look for light-gun signals, but the engine lost power as power was increased. The passenger noticed smoke emanating from the lower engine compartment. Both occupants exited the airplane and called the control tower via mobile phone to report the fire.
Maintenance and Examination
The airplane had undergone recent maintenance requiring removal of the No. 1 alternator to access an adjacent engine cylinder. A postaccident examination by an FAA Airworthiness Inspector revealed that the grounded shield wire for the main power-out cable had been mistakenly attached to the auxiliary power terminal on the No. 1 alternator instead of the alternator's case-ground connection. Extensive fire and heat damage occurred to the No. 1 alternator wire harness, associated ground buss, and main control unit connectors. The stainless steel heat shield and composite firewall also sustained fire and heat damage requiring major repair.
According to the FAA inspector, the aviation mechanic who removed the No. 1 alternator did not mark or identify the location of the wire harness leads during removal. The mechanic referenced the Aircraft Wiring Manual (AWM) and Aircraft Maintenance Manual (AMM) before reinstalling the alternator but was unable to determine the proper placement of the leads using available documentation. The mechanic consulted a co-worker about the grounded shield connector, which was partially obscured by shrink-wrap and not readily identifiable as a shield wire. The decision was made to install the grounded shield wire to the auxiliary power terminal, which provides one-third of the total output capacity of the 100-ampere alternator.
Manufacturer Response
According to the airplane manufacturer, a historical review of electrical schematics, airplane build records, and supporting engineering documentation established that the No. 1 alternator power shield wire was incorporated in the SR22 and SR22T fleets to address electromagnetic interference on airplanes equipped with a 100-ampere No. 1 alternator, storm scope, and air-conditioning. A review of the AWM confirmed that the auxiliary power terminal and the optional power and field shield wires were not depicted in the electrical schematic and supporting documentation. As a result of the accident, the manufacturer updated the AWM alternator wiring depiction to explicitly account for the grounding shield wires and the unused auxiliary power terminal. Additionally, the AWM and AMM were updated to include a caution message stating, "Do not install cable shielding wire(s) to the AUX power terminal." The updated AMM also included a caution: "Cable shielding could be installed to the power and/or field wire harness. If installed, attach cable shielding wire(s) to ground terminal on alternator."