R44 Ditched After Loss of TGB & TR: Improper Maintenance (N1241W, Air Adventures Helicopters, Key West)

On 17 June 2019 Robinson R44 N1241W of Air Adventures Helicopters was ditched off Key West, Florida following the in-flight loss of its Tail Gear Box (TGB) and tail rotor during a Part 91 revenue sightseeing flight.  The three occupants were all uninjured.

Robinson R44 N1241W of Air Adventures Helicopters Ditching off Key West, FL

Robinson R44 N1241W of Air Adventures Helicopters Ditching off Key West, FL (Credit: Unknown)

History of the Flight

The US National Transportation Safety Board (NTSBsafety investigation report explains that:

As the helicopter climbed through 300 ft AGL, the pilot [aged 29, 1430 flying hours total, 1274 on type] detected “rapid tail vibrations.” The pilot radioed tower and requested a return to the airport. He proceeded back to the airport when he heard a loud pop and felt a “hard” right yaw. Attempts to regain control of the helicopter with the anti-torque pedals were ineffective.

He initiated an autorotation, and the helicopter began to yaw to the left. Again, attempts to regain control of the helicopter were ineffective. As the helicopter descended toward the water, the pilot deployed the floats, and landed the helicopter upright on the water without further incident.

Safety Investigation

Examination of the helicopter revealed that the tail rotor assembly had separated from the tail boom…

As well as losing the means of yaw control this will have also resulted in a significant forward shift in centre of gravity, adding to the challenges the pilot faced.

[E]xamination of the mounting hardware between the TGB input cartridge and the tail boom mating flange found that two of the four bolts were missing; both missing bolts came from the right side of the connection. The left side bolts remained secured in place. The missing bolts’ holes in the input cartridge were deformed and were out of round. All of the 4 bolt holes on the input cartridge displayed imprints from the bolt threads, with the deepest imprints on the right sides of the holes, consistent with movement between the lug holes and the bolt shanks. All tail boom flange bolt holes were examined and found that the threading was present, not stripped, and locking inserts present.

The NTSB reveal that c60 flying hours and 5 weeks earlier the tail boom assembly had been removed and replaced.

As part of this maintenance, the tail rotor input cartridge and gearbox would have been removed from the old tailboom and placed on the new tailboom. It is likely that, during this procedure, the right-side mounting bolts were not completely secured to the tail boom casting locking inserts and properly torqued [the the required 240 in-lbs], which resulted in the failure of the right side mounting bolts.

The NTSB report unfortunately contains no further detail on the conduct of this maintenance.

Following the replacement of the tail boom, the pilot reported rapid tail rotor vibrations which required multiple attempts to successfully balance the tail rotor as part of the post maintenance checks.

NTSB Probable Cause

The failure of maintenance personnel to properly secure the right-side tail boom mounting bolts which resulted in the failure of the bolts and an inflight separation of the tail rotor.

Safety Resources

The European Safety Promotion Network Rotorcraft (ESPN-R) has a helicopter safety discussion group on LinkedIn.  You may also find these Aerossurance articles of interest:


Aerossurance worked with the Flight Safety Foundation (FSF) to create a Maintenance Observation Program (MOP) requirement for their contractible BARSOHO offshore helicopter Safety Performance Requirements to help learning about routine maintenance and then to initiate safety improvements:


Aerossurance can provide practice guidance and specialist support to successfully implement a MOP.

Aerossurance’s Andy Evans was recently interviewed about safety investigations, the perils of WYLFIWYF (What-You-Look-For-Is-What-You-Find) and some other ‘stuff’ by with Sam Lee of Integra Aerospace:


Aerossurance has extensive air safety, operations, SAR, airworthiness, human factors, aviation regulation and safety analysis experience.  For practical aviation advice you can trust, contact us at: enquiries@aerossurance.com