Manteo, NC, USA
N400LE
BEECH A24
Shortly after takeoff on the instructional flight, the pilot receiving instruction heard a "pop" sound; the flight instructor saw smoke coming from the right lower portion of the instrument panel and felt a melted wire contact her leg. The pilot receiving instruction continued to fly the airplane briefly, then the flight instructor took the controls. With inadequate runway remaining ahead on which to land, the instructor initiated a turn to return to the runway. The airplane impacted the ground and slid about 500 ft, coming to rest upright and resulting in substantial damage to the airframe. Postaccident examination of the cockpit revealed that electrical wires of a recently-installed avionics switch had arced against the top aft edge of the adjacent autopilot control unit and also at the edge of a vertical support member. The wires did not have circuit protection, nor was there any mechanical protection or supports present along the length of the wires to prevent chafing, contrary to FAA guidance. The pilots' failure to secure the electrical system from memory in response to the cockpit smoke would not have mitigated the hard landing, but may have decreased the smoke in the cockpit and lessened the urgency to land.
On October 18, 2017, about 1000 eastern daylight time, a Beech A24R, N400LE, was substantially damaged when it was involved in an accident near Manteo, North Carolina. The private pilot undergoing instruction (PUI) sustained serious injuries while the flight instructor sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor, who was seated in the right seat, stated that there were no discrepancies with the airplane during the preflight inspection or engine run-up before takeoff. The PUI stated that that about 3 seconds after rotation when the flight was about 1/2 way down the runway at no more than 10 to 15 ft above the runway with the landing gear extended, he heard a "pop" sound from inside the airplane that was not over the intercom. He attributed the sound to be consistent with the tripping of a circuit breaker, though he did not look at the circuit breakers. He did not change the landing gear position and continued flying the airplane. There was no discussion at that time about landing straight ahead, though that would not have been possible based on the airplane's location, and speed. The flight instructor further stated that the flight was at 100 ft and at that time the cockpit filled with smoke and electrical wires on her side of the cockpit were on fire and contacting her leg. The PUI verbalized fire 3 times, which she agreed, and he reportedly asked if she wanted him to secure the battery and alternator switches, to which she verbalized aloud yes because they lost the capability to communicate on the intercom. She indicated that he initially turned off the battery, then later turned off the alternator switches, while the PUI indicated that the battery, alternator and avionics switches remained on until he secured them postaccident because she did not reply to his hand motions on the battery switch. She took the controls from the PUI and when near the VOR antenna executed a 180° turn to return to the runway. The PUI indicated that she was not rolled out of the turn and did not arrest the rate of descent impacting the ground while in a slight left wing and nose low attitude, which the flight instructor characterized as a hard landing. She had previously experienced smoke in a cockpit before and wanted to get the airplane on the ground. She also indicated that it happened quickly which did not allow enough time to complete any checklist, adding that the emergency procedures section of the Pilot's Operating Handbook did not contain a checklist for an "electrical in-flight fire." Neither she or the PUI felt airframe buffet or recalled hearing the stall warning system. Examination of the accident site by several Federal Aviation Administration (FAA) inspectors revealed the airplane first impacted on airport property east of runway 17 near the approach end of the runway. The airplane came to rest upright about 500 ft and 212° from the initial impact location. Examination of the cockpit by a FAA airworthiness inspector revealed a wire with melted insulation hanging from under the right side of the instrument panel. The airplane was recovered and secured for further examination. Postaccident examination of the airplane following recovery was performed by a representative of the airframe manufacturer with oversight from the Federal Aviation Administration. Examination of the cockpit revealed an avionics switch and associated electrical wiring was located at the top center portion of the instrument panel above the autopilot control unit. The electrical wires from the switch were 14 gauge and the markings were different from the airplane's original wires consistent with installation of the switch on April 12, 2017. Following removal of the instrument glare shield, no evidence of fire was noted behind the instrument panel. Further examination of the avionics switch revealed one attached electrical wire connected to the electrical bus bar which was co-located with the landing gear circuit breaker. The other attached electrical wire connected to the "COM 2" circuit breaker. Both electrical wires exhibited evidence of electrical arcing where both crossed over the top aft edge of the autopilot control unit and also at the edge of a vertical support member. The majority of insulation of the electrical wire from the bus bar to the avionics switch was melted or completely missing, while portions of insulation of the electrical wire from the "COM 2" circuit breaker to the avionics switch exhibited melting where it was located in proximity to the other electrical wire. Further examination of the electrical wires associated with the avionics master switch revealed they were tie wrapped together at various places and were also tie wrapped to a larger wire bundle near the bus bar, but there was no mechanical protection or supports present along the length of the wires. Additionally, no circuit protection was observed between the bus bar and the avionics switch. Following removal of the switch and wires from the airplane, the wires had a distinct bend where they passed around the vertical support member. Since installation of the switch, the airplane had accrued about 96 hours. Paragraph 11-47 of Advisory Circular (AC) 43.13-1B specifies that all electrical wires must be provided with some means of circuit protection (circuit breakers or fuses) located as close as possible to the electrical power source bus. Paragraph 11-96(b) of the same AC indicated that metal stand-offs must be used to maintain clearance between wires and structure, while (q) of the same paragraph indicated "Ensure that wires and cables are routed in such a manner that chafing will not occur against the airframe or other components."
The failure of maintenance personnel to properly secure wiring during an electrical component installation, which resulted in arcing and smoke in the cockpit. Contributing to the outcome was the flight instructor's failure to attain a proper descent rate during the forced landing.
Source: NTSB Aviation Accident Database
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