Aviation Investigation Final Report
|
Location:
|
Glacier View, Alaska
|
Accident Number:
|
ANC24LA013
|
|
Date & Time:
|
February 11, 2024, 11:30 Local
|
Registration:
|
N74868
|
|
Aircraft:
|
ROBINSON HELICOPTER
COMPANY R44 II
|
Aircraft Damage:
|
Substantial
|
|
Defining Event:
|
Sys/Comp malf/fail (non-power)
|
Injuries:
|
1 None
|
|
Flight Conducted Under:
|
Part 91: General aviation - Business
|
|
|
Analysis
The pilot stated that he was flying the helicopter solo with the doors removed while scouting potential locations for an aerial photography flight scheduled for later that day. During cruise flight, he heard a loud“boom”and felt a slight airframe vibration. He subsequently lost tail rotor thrust and performed an autorotation to an area of snow-covered, mountainous terrain.
Examination revealed the tail rotor driveshaft was fractured between the forward and aft flex plates. Further examination of the tail rotor driveshaft revealed the fractures were consistent with ductile tension overload. There was no evidence of pre-existing cracks or other damage to the fracture surfaces. The tail rotor blades were not damaged during the accident sequence, and there were no mechanical anomalies found with the tail rotor gearbox assembly.
The torsional twisting of the fractured surfaces of the tail rotor driveshaft is consistent with a sudden binding of the tail rotor gearbox, or a rapid deceleration of the tail rotor blades. There was no damage evident to the tail rotor assembly from a bird strike or impact with a hard object.
Although, if a small rag or towel was overlooked during the preflight inspection and it had blown out of the helicopter during the doors-off flight, it likely would have been struck by the tail rotor, resulting in the rapid deceleration of the tail rotor blades, with little to no detectable damage. Thus, the reason for the torsional fracture of the tail rotor driveshaft could not be determined.
Probable Cause and Findings
The National Transportation Safety Board determines the probable cause(s) of this accident to be:
A sudden stoppage of the tail rotor for unknown reasons, which resulted in the tortional overload failure of the tail rotor driveshaft.
Figure 1. View of the tail rotor driveshaft fracture surfaces
On February 11, 2024, about 1130 Alaska standard time, a Robinson Helicopter R44 II, N74868, was substantially damaged when it was involved in an accident near Glacier View, Alaska. The pilot was not injured. The helicopter was operated as a Title 14 Code of Federal
Regulations Part 91 business flight.
According to the pilot, while in cruise flight with both aft doors removed, about 700 ft above an area of snow-covered glacial terrain, he heard a loud“boom”noise and felt a slight airframe vibration. The pilot stated that he subsequently lost tail rotor thrust and that he then performed an autorotation to an area of snow-covered, mountainous terrain.
A postaccident inspection, after the helicopter was recovered, revealed that the tail rotor driveshaft was fractured between the forward and aft flex plates, which resulted in substantial damage to the tail rotor driveshaft system.
The fractured pieces of the tail rotor driveshaft were sent to the NTSB Materials Laboratory for further examination. The examination revealed the fractures were consistent with ductile torsion overload. There was no evidence of pre-existing cracks or other damage to the driveshaft surfaces. The tail rotor blades were not damaged.
The tail rotor gearbox assembly was removed from the accident helicopter and no anomalies were discovered.
The pilot stated that he did not have a passenger, but that he did have the doors off in preparation for a passenger/photographer later that day. He also stated that during his preflight inspection, he checked for loose items that could blow out and strike the tail rotor.
The pilot did not submit the National Transportation Safety Board Pilot/Operator Aircraft Accident/Incident Report Form 6120.1.
Pilot Information
|
Certificate:
|
Commercial; Flight engineer;
Remote
|
|
Airplane Rating(s):
|
Single-engine land; Multi-engine
land
|
|
Other Aircraft Rating(s):
|
Helicopter
|
|
Instrument Rating(s):
|
Airplane
|
|
Instructor Rating(s):
|
Airplane single-engine; Helicopter
|
|
Medical Certification:
|
Class 2 Without
waivers/limitations
|
|
Occupational Pilot:
|
Yes
|
|
Flight Time:
|
(Estimated) 5000 hours (Total, all aircraft)
|
Aircraft and Owner/Operator Information
|
Aircraft Make:
|
ROBINSON HELICOPTER
COMPANY
|
Registration:
|
N74868
|
|
Model/Series:
|
R44 II
|
Aircraft Category:
|
Helicopter
|
|
Year of Manufacture:
|
|
Amateur Built:
|
|
|
Airworthiness Certificate:
|
Normal
|
Serial Number:
|
11038
|
|
Landing Gear Type:
|
Skid
|
Seats:
|
4
|
|
Date/Type of Last Inspection:
|
Unknown
|
Certified Max Gross Wt.:
|
|
|
Time Since Last Inspection:
|
|
Engines:
|
1 Reciprocating
|
|
Airframe Total Time:
|
|
Engine Manufacturer:
|
LYCOMING
|
|
ELT:
|
|
Engine Model/Series:
|
IO-540 SER
|
|
Registered Owner:
|
SHEEP MOUNTAIN AIR LLC
|
Rated Power:
|
300 Horsepower
|
|
Operator:
|
SHEEP MOUNTAIN AIR LLC
|
Operating Certificate(s)
Held:
|
On-demand air taxi (135)
|
Meteorological Information and Flight Plan
|
Conditions at Accident Site:
|
Visual (VMC)
|
Condition of Light:
|
Day
|
|
Observation Facility, Elevation:
|
AZK,2953 ft msl
|
Distance from Accident Site:
|
21 Nautical Miles
|
|
Observation Time:
|
10:56 Local
|
Direction from Accident Site:
|
|
|
Lowest Cloud Condition:
|
|
Visibility
|
10 miles
|
|
Lowest Ceiling:
|
None
|
Visibility (RVR):
|
|
|
Wind Speed/Gusts:
|
4 knots /
|
Turbulence Type
Forecast/Actual:
|
None / None
|
|
Wind Direction:
|
240°
|
Turbulence Severity
Forecast/Actual:
|
N/A / N/A
|
|
Altimeter Setting:
|
29.49 inches Hg
|
Temperature/Dew Point:
|
-9°C / -9°C
|
|
Precipitation and Obscuration:
|
|
|
|
|
Departure Point:
|
Glacier View, AK (PVT)
|
|
Destination:
|
Glacier View, AK (PVT)
|
Type of Clearance:
|
None
|
|
Departure Time:
|
|
Type of Airspace:
|
Unknown
|
Airport Information
|
Airport:
|
Ridgeline NONE
|
Runway Surface Type:
|
|
Airport Elevation:
|
|
Runway Surface Condition: Snow
|
|
Runway Used:
|
|
IFR Approach: None
|
|
Runway Length/Width:
|
|
VFR Approach/Landing: Forced
landing;Precautionary
landing
|
Wreckage and Impact Information
|
Crew Injuries:
|
1 None
|
Aircraft Damage:
|
Substantial
|
|
Passenger Injuries:
|
N/A
|
Aircraft Fire:
|
None
|
|
Ground Injuries:
|
|
Aircraft Explosion:
|
None
|
|
Total Injuries:
|
1 None
|
Latitude, Longitude:
|
61.661298,-147.58215
|
READ MORE ROTOR PRO: https://justhelicopters.com/Magazine
WATCH ROTOR PRO YOUTUBE CHANNEL: https://buff.ly/3Md0T3y
You can also find us on
Instagram - https://www.instagram.com/rotorpro1
Facebook - https://www.facebook.com/rotorpro1
Twitter - https://twitter.com/justhelicopters
LinkedIn - https://www.linkedin.com/company/rotorpro1