ANC17LA013 · Robinson Helicopter R22
Castor Aviation Robinson Helicopter R22 · Accident during landing
From Wolf Lake Airport (4AK6) to Wolf Lake Airport (4AK6)
Event
- NTSB case
- ANC17LA013
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Robinson Helicopter R22
- Aircraft type
- Robinson R22
- Category
- Helicopter
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N121MR
- Operator
- Castor Aviation
- Onboard fatalities
- Unknown
- Route
- From Wolf Lake Airport (4AK6), Palmer, AKTo Wolf Lake Airport (4AK6), Palmer, AK
- Aircraft age
- About 31 years (built 1985)
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Landing
- Defining eventThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Miscellaneous/other
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Aircraft › Aircraft oper/perf/capability
- Personnel issues › Action/decision
- Personnel issues › Psychological
- Personnel issues › Task performance
Approximate · Coordinates as recorded by the NTSB; no uncertainty radius is established.
NTSB narrative
The flight instructor stated that he was providing flight instruction to the private pilot, practicing pinnacle landings to an area of remote, snow-covered mountainous terrain. The flight instructor said that just before the accident, the private pilot accomplished two successful pinnacle landings. After a third pinnacle landing site was selected, a gravel-covered site on a mountain ridgeline, the private pilot circled the site several times for reconnaissance. He reported that as the helicopter neared the site, about 10 to 20 feet above the surface, he realized that it had a steep uphill grade making the site unsuitable for landing. He explained that, as he was getting ready to tell the private pilot to initiate a go-around, the low rotor revolutions per minute (RPM) warning light and horn activated. The private pilot reported that when the low rotor RPM warning light and horn activated, he observed the gauge indicated about 90 percent RPM.
The flight instructor then took control of the helicopter, attempting to maneuver it to the right and towards the predetermined escape route, but it descended and the skids subsequently struck the uneven terrain. He said that after the initial collision, he increased collective pitch and applied right cyclic, but it began to spin to the right, while descending. The helicopter continued to spin, while descending, and it subsequently struck an area of steep, snow-covered terrain. The helicopter then rolled downhill multiple times before coming to rest in an area of steep, snow-covered terrain.
Probable cause
The pilot's failure to maintain main rotor revolutions per minute (RPM) during a pinnacle landing, which resulted in a main rotor stall condition, a loss of control, and a subsequent impact with terrain. A contributing factor was the flight instructor's failure to monitor the main rotor RPM during the pinnacle landing.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record ANC17LA013
- Event ID
- 20161219X44123
- Case number
- ANC17LA013
- Dataset
- full-current
- Source SHA-256
- 5cf380f0061817c0331a6b2d8cc7e0ee3a79bea469a1001dc5c10e56f35f5ab3
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: investigation status. Values present in the bulk record are kept.
- The date is the local date, which is the same as the UTC date the NTSB stores.
- API snapshot SHA-256: 8fb9289bb5a7096321f667e6e76650c4e72699a564abc8e3d6ef21952ddecea8; retrieved 2026-09-16T04:54:12.915Z.