McKinleyville, CA, USA
N661TC
PIPER PA-31T
About 13 minutes after takeoff for a medical transport flight, while climbing through about 14,900 ft mean sea level (msl), the pilot reported to air traffic control (ATC) that he was smelling smoke in the cockpit and would be returning to the originating airport. The flight was cleared to return with a descent at pilot's discretion to 9,000 ft msl. The pilot replied, "okay," and said that it looked like he was going to lose some power shortly. The pilot then stated that he had smoke in the cockpit, declared an emergency, and requested that ATC contact the fire department. About 1 minute 15 seconds after the initial report of smelling smoke, the pilot made the last radio transmission of the flight stating that he had three people on board. The wreckage was located about 9 hours later in an area of brush and heavily forested terrain. Portions of the burned and fragmented wreckage were scattered along a debris path that measured about 2,400 ft in length, which is consistent with an inflight breakup. The center fuselage and cockpit areas were largely intact and displayed no evidence of fire; however, there was an area of thermal damage to the forward fuselage consistent with an inflight fire. The thermal damage was primarily limited to the floor area between the two forward seats near the main bus tie circuit breaker panel and extended to the forward edge of the wing spar. All exposed surfaces were heavily sooted. Some localized melting and thermal-related tearing of the aluminum structure was present. The primer paint on the floor panels under the right aft corner of the pilot seat and the left aft corner of the co-pilot seat was discolored dark brown. An aluminum stringer in this location exhibited broomstrawing indicating that the stringer material was heated to near its melting point prior to impact. A single wire located in the area exhibited notching consistent with mechanical rubbing. The main bus tie circuit breakers were partially missing. The remaining breakers were heavily sooted on their aft ends, and one breaker was thermally discolored. Areas of charring were on the backside of the panel. Examination of the wiring in this area showed evidence of electrical arcing damage. Four hydraulic lines servicing the landing gear system were located in this area, and all the lines exhibited signs of thermal exposure with melting and missing sections of material. Six exemplar airplanes of the same make and model as the accident airplane were examined, and instances of unsafe conditions in which electrical lines and hydraulic lines in the area of the main bus tie circuit breaker panel were in direct contact were found on all six airplanes. Some of the wires in the exemplar airplanes showed chafing between hydraulic lines and the electrical wires, which, if left uncorrected, could have led to electrical arcing and subsequent fire. Based on the unsafe conditions found during examination of the exemplar airplanes and the thermal damage to the area near the main bus tie circuit breaker panel on the accident airplane, including broomstrawing of the aluminum structure, electrical arcing damage to the wiring, and melting of the hydraulic lines, it is likely that an electrical wire near the tie bus circuit breakers chafed on a hydraulic line and/or airplane structure, which resulted in arcing and a subsequent in-flight fire that was fed by the hydraulic fluid.
HISTORY OF FLIGHTOn July 29, 2016, about 0105 Pacific daylight time, a Piper PA-31T Cheyenne II airplane, N661TC, broke up in flight and impacted the ground shortly after the pilot reported smoke in the cockpit near Arcata/Eureka Airport (KACV), McKinleyville, California. The airline transport pilot, two medical personnel, and the patient were fatally injured. The airplane was destroyed. The airplane was being operated by Cal-Ore Life Flight as an instrument flight rules (IFR) air ambulance flight under the provisions of Title 14 Code of Federal Regulations Part 135 when the accident occurred. Instrument meteorological conditions prevailed, and company flight following procedures were in effect. The flight departed Jack Mc Namara Field (KCEC), Crescent City, California, at 0045 destined for Oakland International Airport (KAOK), Oakland, California. A postaccident review of Federal Aviation Administration (FAA) radar data and voice communication revealed that, the medical transport flight, which was using the call sign Lifeguard November (LN) 661TC, departed KCEC, was radar identified by air traffic control, was instructed to climb to 15,000 ft mean sea level (msl), and was cleared to KAOK as filed. At 0058:13, the pilot contacted the Seattle Air Route Traffic Control Center (ZSE) controller working the flight and stated that he was going to turn back to Crescent City and that he was smelling smoke in the cockpit. Radar data indicated that the airplane's altitude about that time was 14,900 ft msl, and the airplane was on a southeast heading. At 0058:25, the ZSE controller cleared the pilot direct to Crescent City, issued him a descent at pilot's discretion to 9,000 ft msl, and told the pilot to inform her if he needed anything else. Radar data indicated that the pilot initiated a right turn to a northwest heading about that time, which continued until about 0059:50. At 0058:42, the pilot said that it looked like he was going to lose some power shortly and that he would keep the controller posted as long as he could. At 0058:53, the controller issued the pilot the Crescent City altimeter setting of 29.98 and requested the number of souls on board and fuel remaining. At 0059:07 the pilot stated that he had smoke in the cockpit, declared an emergency, was depressurizing and heading back to Crescent City, and asked the controller to call the fire department. At 0059:24, the controller replied that she would and asked again how many people were on board the airplane. The airplane's altitude fluctuated between 14,900 ft and 15,400 ft between 0058:14 and 0059:26. About 0059:26, the radar data indicated that the airplane was on a northwest heading at an altitude of 15,200 feet msl when Mode C radar data was lost, and no further altitude information was received. At 0059:28, the pilot stated that he had three souls on board. There were no further communications from the pilot despite multiple attempts by ATC controller. From about 0059:38 to 01:00:50, primary radar data returns corresponding to the airplane's position indicated that the airplane continued on a northwest heading, followed by a left turn to a southeast heading. From 01:01:26 to 01:02:02, the airplane continued on a southeast heading. It then began a gradual right turn to a west heading that continued until 01:02:50 when the airplane was lost from radar; the airplane at that time was located at about 53.5 miles south of KCEC and about 6 miles northeast of KACV. An alert notice was issued by the FAA at 0210, and an extensive search was launched. Search operations were conducted by personnel from the U.S. Air Force Search and Rescue, California Highway Patrol, U.S. Coast Guard, and the Humboldt County Sheriff's Office. About 1011, searchers located portions of the heavily fragmented wreckage that were positively identified as belonging to the airplane at 1029. During a telephone conversation with an NTSB investigator, a witness located near Cookson Camp, Arcata, California, reported that, in the early morning hours of July 29, she heard an airplane circle overhead before proceeding westward followed by about 15 seconds of silence. While looking out the window of her tent, she saw a large dome-shaped flash to the west, followed by another flash and a loud rumble. PERSONNEL INFORMATIONThe pilot, age 54, held an airline transport pilot certificate with an airplane multi-engine land rating. Additionally, he held commercial pilot privileges for airplane single-engine land and rotorcraft-helicopter. He also held a type rating for A/BE-1900 airplanes and a certified flight instructor certificate with airplane single-engine land, multi-engine land, instrument airplane, and rotorcraft-helicopter ratings. His most recent second-class medical was issued on July 25, 2016, with the limitation that he must have available glasses for near vision. According to the operator's training records, the pilot completed training and was assigned for duty as a pilot-in-command in Piper PA-31T aircraft on May 12, 2016. He was hired with 7,300 hours total flight time, 1,378 hours of actual IFR, 179 hours of simulated IFR, 3,178 hours of night time, 5,174 hours of VFR cross country, and 3,100 hours of night cross country. In addition, at the time of the accident, he had accumulated about 125.5 hours in the accident airplane make and model. His most recent airman competency/proficiency check, which was administered by a company check airman, was completed on May 12, 2016. The pilot's flight and duty records revealed the he was off duty on July 25 and 26. On July 27, his duty day started at 1700 and ended on July 28 at 0500, and he flew 3 hours 40 minutes. On July 28, his duty day started at 1700, and he flew 2 hours 05 minutes before the accident. AIRCRAFT INFORMATIONThe airplane was manufactured in 1981 and was equipped with retractable landing gear, two Pratt and Whitney PT6A-135A engines, and controllable pitch propellers. It was also equipped with a handheld fire extinguisher, smoke goggles, and a LifePort stretcher system that had been installed in conformance with LifePort supplemental type certificate No. SA00528SE. The modification required additional power requirements, which are discussed below. The operator maintained the airplane in accordance with Piper Progressive Inspections on a 100-hour cycle per Piper document 761-664, dated October 27, 1994. The most recent inspection was completed on July 14, 2016, when the airplane had accumulated 7,286.6 hours total time in service. At the time of the accident, the airframe had accumulated 7,309 hours total time in service. Both the left (S/N PZ0641) and right (S/N PZ0642) engines had accumulated 3,712 hours since new. Both the left (S/N 27825) and right (S/N 27829) propeller assemblies had accumulated 1,662 hours since overhaul. Electrical System The Piper PA-31T is equipped with a 28-volt direct current electrical system powered by a battery and two starter generators. External power provisions are available for ground operational requirements. The typical power distribution system is of split-bus design with individual circuit protection and separate pilot-accessible bus-tie circuit breakers that includes diode protection and provides operational flexibility during single-engine or single-generator operation. The main bus tie circuit breakers are located on a panel in the floor between the pilot and copilot seats. The cockpit floor separates the pressurized area (cabin) and the unpressurized area (below the circuit breaker panel). The airplane's panel contained, at the time of delivery, twelve circuit breakers (C/Bs) in two rows of six with current ratings ranging from 50 amps (A) to 200 A. The LifePort modification required the addition of two circuit breakers to the main bus tie panel with ratings of 30 A and 50 A. Based on a review of the airplane wreckage and discussions with the owner, the 50 A C/B "EMS INV" was located next to the "Right Generator" C/B on the first row, and the 30 A C/B "EMS PWR" was located next to the "R Main 2" C/B on the second row. In the structural bay, below the floor where the main bus tie panel was located, additional wiring and components for the left and right starter solenoids were mounted. Hydraulic System The Piper PA-31T is equipped with two hydraulic systems: one for the retractable landing gear and landing gear doors and one for the airplane's braking system. The nominal landing gear system operating pressure is 1900 pounds per square inch, and the landing gear system remains pressurized during gear extension and retraction operations. The hydraulic fluid used in the hydraulic system is MIL-H-5606. A hand pump, located in the cockpit floor just forward of the circuit breaker panel, is installed to serve as an emergency pump in the event of a failure of the engine-driven pumps. The pump is accessed by a door in the cockpit floor, and the handle can be extended to allow pump operation. The pump handle, when in the stowed position, is partially located in the structural bay that contains the electrical circuit breakers. Four hydraulic lines for the main landing gear travel from the hydraulic reservoir, along the fuselage below the floor, through the main spar, and then to the left and right main landing gear actuators and door actuators. A production break of the hydraulic line sections is located below the circuit breaker panel, where each of the lines are joined using AN-type union fittings. Aft of the main spar, the lines connect to AN-type T-fittings and proceed to the main landing gear bays in the left and right wings. Fuel System The Piper PA-31T fuel system consists of independent left and right fuel systems that are connected to each other by a crossfeed system. Each inboard fuel tank contains two submerged fuel boost pumps. One fuel pump must be operating any time its respective engine is in operation in order to supply fuel under pressure to the engine-driven fuel pump. Fuel pump operation for each side is controlled by a three-position switch on the overhead panel. Each set of wing tanks contains a fuel shutoff valve mounted on the inboard side of its respective wing root. The fuel crossfeed valve is mounted on the inboard side of the left wing root. Each valve is operated by a push-pull control lever that is mounted on the cockpit floor against the main spar housing just aft of the circuit breaker panel. The crossfeed fuel system line from the right fuel system to the left fuel system is routed underneath the cockpit floor along the forward face of the main spar. A tee is located in the fuel line along the right side of the airplane in the fuselage to provide fuel for the Janitrol heater located in the nose of the aircraft. No portion of the fuel lines are located in the structural bay that contains the circuit breaker panel. For additional information regarding the airplane's systems refer to the Systems Group Chairman Factual Report located in the public docket for this accident. METEOROLOGICAL INFORMATIONAt 0107, KACV, located about 6 miles southwest of the accident site, was reporting, in part, wind 180° at 4 knots, visibility 1/2 statute mile in mist, runway 32 visual range 4,500 ft variable to greater than 6,000 ft, ceiling 200 ft overcast, temperature 55°F, dew point 54°F, and altimeter 29.85 inches of mercury. AIRPORT INFORMATIONThe airplane was manufactured in 1981 and was equipped with retractable landing gear, two Pratt and Whitney PT6A-135A engines, and controllable pitch propellers. It was also equipped with a handheld fire extinguisher, smoke goggles, and a LifePort stretcher system that had been installed in conformance with LifePort supplemental type certificate No. SA00528SE. The modification required additional power requirements, which are discussed below. The operator maintained the airplane in accordance with Piper Progressive Inspections on a 100-hour cycle per Piper document 761-664, dated October 27, 1994. The most recent inspection was completed on July 14, 2016, when the airplane had accumulated 7,286.6 hours total time in service. At the time of the accident, the airframe had accumulated 7,309 hours total time in service. Both the left (S/N PZ0641) and right (S/N PZ0642) engines had accumulated 3,712 hours since new. Both the left (S/N 27825) and right (S/N 27829) propeller assemblies had accumulated 1,662 hours since overhaul. Electrical System The Piper PA-31T is equipped with a 28-volt direct current electrical system powered by a battery and two starter generators. External power provisions are available for ground operational requirements. The typical power distribution system is of split-bus design with individual circuit protection and separate pilot-accessible bus-tie circuit breakers that includes diode protection and provides operational flexibility during single-engine or single-generator operation. The main bus tie circuit breakers are located on a panel in the floor between the pilot and copilot seats. The cockpit floor separates the pressurized area (cabin) and the unpressurized area (below the circuit breaker panel). The airplane's panel contained, at the time of delivery, twelve circuit breakers (C/Bs) in two rows of six with current ratings ranging from 50 amps (A) to 200 A. The LifePort modification required the addition of two circuit breakers to the main bus tie panel with ratings of 30 A and 50 A. Based on a review of the airplane wreckage and discussions with the owner, the 50 A C/B "EMS INV" was located next to the "Right Generator" C/B on the first row, and the 30 A C/B "EMS PWR" was located next to the "R Main 2" C/B on the second row. In the structural bay, below the floor where the main bus tie panel was located, additional wiring and components for the left and right starter solenoids were mounted. Hydraulic System The Piper PA-31T is equipped with two hydraulic systems: one for the retractable landing gear and landing gear doors and one for the airplane's braking system. The nominal landing gear system operating pressure is 1900 pounds per square inch, and the landing gear system remains pressurized during gear extension and retraction operations. The hydraulic fluid used in the hydraulic system is MIL-H-5606. A hand pump, located in the cockpit floor just forward of the circuit breaker panel, is installed to serve as an emergency pump in the event of a failure of the engine-driven pumps. The pump is accessed by a door in the cockpit floor, and the handle can be extended to allow pump operation. The pump handle, when in the stowed position, is partially located in the structural bay that contains the electrical circuit breakers. Four hydraulic lines for the main landing gear travel from the hydraulic reservoir, along the fuselage below the floor, through the main spar, and then to the left and right main landing gear actuators and door actuators. A production break of the hydraulic line sections is located below the circuit breaker panel, where each of the lines are joined using AN-type union fittings. Aft of the main spar, the lines connect to AN-type T-fittings and proceed to the main landing gear bays in the left and right wings. Fuel System The Piper PA-31T fuel system consists of independent left and right fuel systems that are connected to each other by a crossfeed system. Each inboard fuel tank contains two submerged fuel boost pumps. One fuel pump must be operating any time its respective engine is in operation in order to supply fuel under pressure to the engine-driven fuel pump. Fuel pump operation for each side is controlled by a three-position switch on the overhead panel. Each set of wing tanks contains a fuel shutoff valve mounted on the inboard side of its respective wing root. The fuel crossfeed valve is mounted on the inboard side of the left wing root. Each valve is operated by a push-pull control lever that is mounted on the cockpit floor against the main spar housing just aft of the circuit breaker panel. The crossfeed fuel system line from the right fuel system to the left fuel system is routed underneath the cockpit floor along the forward face of the main spar. A tee is located in the fuel line along the right side of the airplane in
An inflight fire in the floor area near the main bus tie circuit breaker panel that resulted from chafing between an electrical wire and a hydraulic line and/or airplane structure.
Source: NTSB Aviation Accident Database
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