NTSB Final Report: Whiteside, TN

The pilot and the passenger/observer, who were both law enforcement personnel, were flying in a helicopter on a law enforcement mission when it struck a marked, 1-inch diameter, energized (161K volt) aluminum high-tension powerline cable. The high-tension powerlines were about 430 ft tall and about 3,800 ft long. A witness was driving on a nearby interstate when he observed the helicopter flying low and close to the powerlines. The witness reported that he was concerned the helicopter was going to hit the lines. He described the helicopter as hovering, and it did not appear to be in distress. The witness then saw the helicopter strike the powerlines and observed an “arc.” The helicopter spun a few times as it descended and went out of view.

The helicopter came to rest in heavily wooded and steep mountainous terrain, which resulted in substantial damage to the fuselage, main rotor, and tail rotor. A postaccident examination of the airframe and engine revealed no evidence of any preimpact mechanical malfunctions and failures that would have precluded normal operation.

Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot’s failure to maintain clearance from the powerlines.

Personnel issues                            Monitoring environment - Pilot

Aircraft                                               Altitude - Not attained/maintained

Environmental issues                    Wire - Effect on equipment

Factual Information

History of Flight

Maneuvering-low-alt flying            Collision with terr/obj (non-CFIT) (Defining event)

HISTORY OF FLIGHT

On August 23, 2022, about 1447 central standard time, a Bell 206B helicopter, N770HP, was substantially damaged when it was involved in an accident near Whiteside, Tennessee. The pilot and the passenger/observer were fatally injured. The flight was conducted as a Title 14 Code of Federal Regulations Part 91 public aircraft operation.

The helicopter was operated by the Tennessee Department of Safety. The pilot, who was an officer with the Tennessee Department of Safety, and the passenger/observer, who was a detective with the Marion County (TN) Sheriff’s Department, struck a marked, 1-inch diameter, energized (161K volt) aluminum high-tension powerline cable while en route to rejoin a marijuana eradication mission. The high-tension powerlines were about 430 ft tall and about 3,800 ft long.

According to the Tennessee Department of Safety, the pilot and the passenger/observer had been conducting a joint-agency marijuana eradication mission that day and stopped for lunch and fuel at the Marion County Airport (APT) in Jasper, Tennessee, at 1248. The pilot purchased 48 gallons of Jet A at 1251. After lunch, a call came in requesting back up for a pursuit that the Tennessee Department of Safety was engaged in. The pilot felt the pursuit would be over before they arrived to assist. Then a call came in about a missing person case that the passenger/observer was working and was not associated with the eradication mission. The pilot and passenger/observer departed at 1401 and flew to a set of coordinates (a hotel) of where the missing person was believed to be. The missing person was not located, and the helicopter returned to join the eradication efforts. It was on this return flight that the helicopter struck the powerlines.

A witness was driving eastbound on Highway 24 toward Chattanooga, Tennessee, when he observed a “dark colored helicopter” flying westbound just north of the interstate. He was talking on the phone to his wife at the time and he told her how concerned he was that the helicopter was flying so low and very close to a set of powerlines. He described the helicopter as hovering, and it did not appear to be in distress. The witness then saw the helicopter strike the powerlines and observed an “arc.” The helicopter spun a few times, and it appeared as if the pilot was trying to regain control of the helicopter. The witness said the helicopter then descended and went out of view. At the same time, a broken section of a powerline cable fell on the interstate in front of his vehicle.

AIRCRAFT INFORMATION

The Bell 206B is a two-bladed, 5-seat helicopter powered by a single Rolls Royce 250-C20J turbine engine. The Tennessee Department of Safety owned and operated the helicopter as a public use aircraft.

The helicopter was maintained by the Tennessee Department of Safety under a continuous inspection program. A review of the engine maintenance logbook revealed the last entry was made on August 15, 2022. At that time, a 150/300 engine inspection was completed as per the Rolls Royce Maintenance Manual. The aircraft total time (ACTT) was 5,668.0 hours and the engine total time (ETT) was also 5,668.0 hours.

Each pilot was required to check into an electronic maintenance database prior to flight to record the ACTT. The last entry made for N770HP was on the day of the accident. The ACTT entered was 5,674.0 hours.

WRECKAGE EXAMINATION

The helicopter came to rest in heavily wooded and steep mountainous terrain on the west side of the powerlines. The nose of the helicopter was embedded in the ground on a ravine wall with the tail section pointed straight up in the air. There was no post-impact fire. The tail boom (minus the tail rotor) separated from the helicopter just aft of the horizontal stabilizer and was located downhill of the helicopter. This section of tail boom exhibited a downward slanting impact mark consistent with contact of the main rotor blade.

The helicopter was equipped with aftermarket composite tail rotor blades. The tail rotor (minus one blade) was located approximately 100 ft east of where the helicopter came to rest and under the powerlines. Damage to the tail rotor and tail rotor gearbox was consistent with impact damage. The other tail rotor blade was not located. The top portion of the vertical stabilizer had also separated from the helicopter and was found under the powerlines and adjacent to a set of train tracks located north of where the helicopter came to rest. The fractured area of the vertical stabilizer exhibited striated gouging marks consistent with contact with powerlines.

The cockpit area and forward fuselage sustained extensive impact damage. Only the right side (pilot seat) was equipped with a cyclic and collective; however, both sets of anti-torque pedals were installed. Both sets of pedals had separated from their respective control tubes from impact. The cyclic had separated at its base due to impact and was found in the wreckage. The collective was fractured from impact but remained partially attached at its base, and the throttle (twist grip) was loose.

Examination of the flight control system from the cockpit to the main rotor and tail rotor revealed numerous impact fractures to the control tubes/linkages, but each fracture was consistent with overload from impact with terrain. Examination of the helicopter revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation.

The two main rotor blades were marked with either a red or white dot to differentiate between the two blades. The white blade remained partially attached at the trailing edge and the spar was fractured just outboard of the doubler. This blade was cut at the trailing edge for recovery purposes. The red blade separated just outside the doubler and was found uphill of where the helicopter came to rest.

Examination of the white blade revealed striated impact marks on the bottom of the blade about 2/3 outboard of the blade root. These striated marks were consistent with impact with the powerline. Striation marks were also observed on the top of the blade but were not as pronounced. The red blade exhibited arcing at the trailing edge tip of the blade.

The engine remained secured to the helicopter and none of the engine mounts were damaged. Examination of the engine revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation.

Pilot Information

Aircraft and Owner/Operator Information

Meteorological Information and Flight Plan

Wreckage and Impact Information

Administrative Information

The National Transportation Safety Board (NTSB) is an independent federal agency charged by Congress with investigating every civil aviation accident in the United States and significant events in other modes of transportation— railroad, transit, highway, marine, pipeline, and commercial space. We determine the probable causes of the accidents and events we investigate, and issue safety recommendations aimed at preventing future occurrences. In addition, we conduct transportation safety research studies and offer information and other assistance to family members and survivors for each accident or event we investigate. We also serve as the appellate authority for enforcement actions involving aviation and mariner certificates issued by the Federal Aviation Administration (FAA) and US Coast Guard, and we adjudicate appeals of civil penalty actions taken by the FAA.

The NTSB does not assign fault or blame for an accident or incident; rather, as specified by NTSB regulation, “accident/incident investigations are fact-finding proceedings with no formal issues and no adverse parties … and are not conducted for the purpose of determining the rights or liabilities of any person” (Title 49 Code of Federal Regulations section 831.4). Assignment of fault or legal liability is not relevant to the NTSB’s statutory mission to improve transportation safety by investigating accidents and incidents and issuing safety recommendations. In addition, statutory language prohibits the admission into evidence or use of any part of an NTSB report related to an accident in a civil action for damages resulting from a matter mentioned in the report (Title 49 United States Code section 1154(b)). A factual report that may be admissible under 49 United States Code section 1154(b) is available here.