Preliminary Reports

Unsecured Bearing Was Recently Replaced

Airbus Helicopters AS350, May 1, 2024, Plant City, Florida

Following a low-altitude loss of yaw control that necessitated an emergency autorotation in a field, investigators discovered that the aftmost hanger bearing supporting the tail rotor drive shaft had not been properly secured. One of the two bolts holding it in place was found loose in the tailboom; the other was still in place, but its nut was not correctly seated. All five hanger bearings had been replaced during scheduled maintenance some 12.3 flight hours earlier.

The helicopter was operated by the Hillsborough County Sheriff’s Office.

During a positioning flight from Lakeland Linder International Airport, the 2,322-hour commercial pilot chose a field to practice confined area approaches and slope landings. Maneuvering in the landing zone at about 50 feet and 20 knots, the helicopter entered a left spin that the pilot could not arrest. His emergency autorotation brought the helicopter upright with the engine still running and no damage to the main rotor blades. The pilot and the 132-hour copilot were not injured and exited the helicopter normally after shutting down the engine.

Aircraft damage included separation of the tail rotor gearbox with damage to one tail rotor blade and “multiple bends and wrinkles in the tailboom.”

No Serious Injuries in Emergency Autorotation

Aerospatiale SA315B, May 27, 2024, Hildale, Utah

The pilot and two of his three passengers escaped with minor injuries following an emergency autorotation to a road in response to a partial loss of engine power. The third passenger was not hurt.

Following a 15- to 20-minute sightseeing flight, the pilot shut down the engine to clean the helicopter’s windscreen before boarding new passengers; he reported that the second takeoff was normal but the aircraft soon felt “sluggish.” He initiated the autorotation after the low RPM warning activated at about 50 feet altitude and 50 knots airspeed.

Video captured by a witness showed flames coming from the exhaust stack from a few seconds after takeoff until the helicopter reached the ground.

Final Reports

Aspen Takeoff Overrun Followed Instantaneous Wind Call

Hawker 800XP, Feb. 21, 2022, Aspen, Colorado

Gusty tailwinds reportedly proved too strong to allow the pilots attempting to take off to lift the twin-jet’s nose at rotation speed at Colorado’s Aspen/Pitkin County Airport. No one was injured after the crew aborted the takeoff and the jet went off the runway and into the snow, although the Hawker was substantially damaged.

According to the NTSB final report, the probable cause of the accident was “the flight crew’s decision to take off in tailwind conditions that were consistently above the airplane’s tailwind limitation, which resulted in a runway overrun following an aborted takeoff. Contributing was the flight crew’s use of the instantaneous wind report for the decision to attempt the takeoff.” Like many business jets, the Hawker’s tailwind takeoff limitation is 10 knots.

When the Hawker was cleared to taxi to Runway 33, the wind was reported at 170 degrees at 18 knots, gusting to 30 knots. After a delay due to arriving traffic, the tower controller cleared the Hawker for takeoff and, according to the NTSB, “reported the wind was from 160 degrees at 16 knots, gusting to 25 knots, and the ‘instantaneous wind’ was from 180 degrees at 10 knots.”

The tower controllers must use the two-minute average wind as the official wind report, based on the standalone weather sensor (SAWS) readings, according to the Aspen tower standard operating procedures (SOPs). Further, “If a pilot requests, the instantaneous wind may be issued after the SAWS two-minute average wind has been given.” The ATIS broadcast is also supposed to include a warning if the wind is above a 10-knot sustained tailwind or gusting above a 15-knot tailwind between headings of 100 to 200 degrees for Runway 33.

However, according to the NTSB, there appears to be no actual definition of “instantaneous wind” and no guidance on whether pilots should use it to try to take off at a moment when the gusts appear to die down enough to avoid exceeding a tailwind limitation. The FAA previously told AIN that “instantaneous wind” gives the pilot a three-second snapshot of current wind conditions.

“‘Instantaneous wind’ is a term used by ASE [Aspen control tower] that is not defined in any FAA publication of record,” the NTSB report noted. “After the accident, the ASE ATM [air traffic manager] was asked why ASE ATC chose to use the phrase ‘instantaneous wind’ when reporting the standalone weather, and the manager stated he was not sure where that [term] had originated. He reported that a few operators routinely request the instantaneous wind reports because of their familiarity with ASE operations.”

According to the NTSB, “Following the accident, the operator informed its flight crews to no longer consider ‘instantaneous wind’ reports in their decision--making process.”

Helicopter Destroyed by 'Unsecured Overalls'

MD Helicopters 500D, Oct. 18, 2018, Wānaka Aerodrome, South Island, New Zealand

An investigation spanning nearly six years ultimately determined that a pair of heavy cold-weather overalls carried loose in the cabin departed the aircraft and flew into the tail rotor after the left rear door opened shortly after takeoff.

The resulting in-flight breakup killed the pilot and two Department of Conservation staff on their way to conduct wildlife culling operations. Police initially treated the accident site as a crime scene due to threats made by opponents of the department’s cull.

Reconstruction of the accident sequence found that the impact separated the tail rotor from the boom, propelling it forward into the main rotor blades. The outer sections of two of the five blades broke off; another then severed the tail boom.

Two experienced flight instructors flying a Robinson helicopter in the traffic pattern saw multiple items leave the cabin before the tail boom bent upwards and separated from the aircraft. Wear on the latch mechanism of the left rear door pointed to its having opened in flight.

King Air Crash Attributed to Tailplane Stall

Beech E90, Oct. 18, 2022, Marietta, Ohio

The NTSB concluded that the twin-engine turboprop’s sudden departure from controlled flight was the result of a tailplane stall caused by ice accumulation.

Both pilots were killed when the airplane entered a spinning, near-vertical descent in the final segment of the RNAV approach to Runway 21 of Mid-Ohio Valley Regional Airport in Parkersburg, West Virginia, crashing into the parking lot of an automobile dealership in neighboring Marietta, Ohio.

Weather studies indicated “a 20% to 80% probability of encountering supercooled large droplets” during the approach. The King Air was certified for flight into known icing, but the extensive damage and post-crash fire made it impossible to determine whether its anti-icing systems were in use.

The 75-nm positioning flight originated at John Glenn Columbus (Ohio) International Airport, maintaining 11,000 feet en route. Communications with Indianapolis Center, Parkersburg Approach, and eventually Parkersburg Tower were routine.

The airplane maintained the minimum crossing altitude of 2,800 feet to the final approach fix, then slowed from 170 to 126 knots. Multiple eyewitnesses saw it flying straight and level before suddenly spinning straight into the ground, a sequence also captured from several different angles by security cameras. 

Published stall speeds for the E90 range from 65 knots with full flaps to 88 knots with flaps retracted.

Tailplane stalls are relatively rare and usually precipitated by icing, which accumulates more readily on the tail than the wings. They cause an abrupt pitching-down moment similar to a wing stall, but the required recovery technique is exactly opposite to the conventional stall recovery.

Training Accident Remains Mysterious

Learjet 35A, May 15, 2023, Hohn Military Airport, Schleswig-Holstein, Germany

The failure of a highly experienced pilot to apply sufficient rudder pressure during a planned simulated engine failure, and that of the similarly experienced pilot monitoring to intervene in time to avert a catastrophic loss of control, were not explained by any findings from the cockpit voice or flight data recorders, and no evidence of mechanical anomaly was found in the wreckage.

The 62-year-old pilot flying, who had logged more than 8,000 hours in Learjets, and the 58-year-old pilot monitoring, who had more than 6,250 hours in type, were killed when they lost yaw control after reducing thrust on the right engine shortly after takeoff.

The 1993-model jet entered a snap roll and crashed inverted next to the runway. Before the simulated engine-out, a required maneuver during recurrent proficiency checks, the pilot monitoring had said, “In advance, you will lose the right engine.”

The accident, described in detail in the October 2023 issue of this report, took place during a larger exercise in which six of the operator’s Learjets were to conduct practice instrument approaches to help train air traffic control staff while also conducting proficiency checks for the pilots flying.

Another company pilot recalled an incident (confirmed by flight data recorder information) in which the wiring behind the rudder pedal in a different Learjet temporarily restricted him from applying full rudder pressure during the same exercise, but its relevance to the accident could not be determined. ζ