ASN Wikibase Occurrence # 170329
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| Date: | Tuesday 7 October 2014 |
| Time: | 08:08 LT |
| Type: |  Robinson R44 Raven II |
| Owner/operator: | Helicopter Charter Karamea |
| Registration: | ZK-HBQ |
| MSN: | 10516 |
| Year of manufacture: | 2004 |
| Fatalities: | Fatalities: 1 / Occupants: 1 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | Mt Arthur, Kahurangi NP -
 New Zealand
|
| Phase: | En route |
| Nature: | Ferry/positioning |
| Departure airport: | Karamea NZKM |
| Nelson NZNS | |
| Investigating agency: | TAIC |
| Confidence Rating: |  Accident investigation report completed and information captured |
At about 08:08 on 7 October 2014, a Robinson R44 helicopter crashed into steep bush to the northeast of Mt Arthur, in the Kahurangi National Park. The helicopter was being flown from Karamea to Nelson for scheduled maintenance, through an area of forecast high winds and turbulence, at the time of the accident.
The helicopter broke up in flight after one of the main rotor blades struck the cabin and the main rotor assembly separated from the rest of the helicopter. The pilot, who was the only occupant, was killed.
The cause of the main rotor strike and subsequent separation was a phenomenon associated with helicopters having two-bladed, semi-rigid teetering main rotor systems, called 'mast-bumping':
- Mast-bumping is where an excessive teetering or 'see-saw' movement of the main rotor causes the inner end (spindle) of the blades to contact the main rotor driveshaft (or mast), while rotating.
Mast-bumping can occur when a helicopter enters a low-gravity (low-G) condition (less than 1G to weightless/zero G), which can be caused by turbulence or induced by flight control inputs.
In-flight break-ups can also be caused by low main rotor revolutions per minute (RPM). However, the Transport Accident Investigation Commission determined that it was very unlikely that low main rotor RPM was a factor in this accident.
The Commission determined that it was very likely that the helicopter entered a low-G condition after crossing the Tasman Ranges downwind from Mt Arthur. Turbulence created by a strong southwest wind likely included severe downdraughts that prolonged the low-G condition, which likely initiated the mast-bumping.
The Commission could not rule out a flight control input as having contributed to the in-flight break-up.
The Commission made the following additional findings:
- had a previous limitation on maximum wind speeds for inexperienced Robinson R44 pilots remained in place, as per that for Robinson R22 pilots, the pilot would have been prohibited from flying at the time of the accident, due to the forecast strong winds and turbulence
- all Robinson helicopter models are susceptible to low-G mast-bumping, and any preventive measures should apply to all of them
- due to their unique main rotor design, during a prolonged or severe low-G condition Robinson helicopters can roll rapidly to the right, and likely break up before a pilot can recover
- a pilot's instinctive reaction to an unexpected right roll, or the unintentional movement of a pilot's limbs or upper body during severe turbulence or low-G, could lead to mast-bumping
- although not an intuitive reaction to a sudden right roll, the aft cyclic technique is the only approved recovery technique, and should be used as soon as low-G is felt to 'reload' the main rotor disc and help reduce any right roll.
Accident investigation:
 |
|
Sources:
https://taic.org.nz/inquiries?SkinSrc=[G]skins/taicAviation/skin_aviation
https://nz.news.yahoo.com/helicopter-goes-missing-near-nelson-25200108.html
https://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11338537
http://home.nzcity.co.nz/news/article.aspx?id=195165&fm=newsmain%2Cnrhl
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 07-Oct-2014 01:47 | angels one five | Added |
| 07-Oct-2014 02:07 | angels one five | Updated [Location, Narrative] |
| 07-Oct-2014 12:33 | Anon. | Updated [Aircraft type, Registration, Cn, Operator, Source] |
| 08-Oct-2014 08:01 | Alpine Flight | Updated [Time, Aircraft type] |
| 10-Oct-2014 07:22 | angels one five | Updated [Time, Total fatalities, Other fatalities, Source, Narrative] |
| 10-Oct-2014 08:17 | Chieftain | Updated [Damage] |
| 09-Apr-2017 19:34 | harro | Updated [Time, Source, Narrative] |
| 23-Jan-2022 03:32 | Ron Averes | Updated [Location] |
| 25-Jan-2022 07:26 | Ron Averes | Updated [Location] |
| 07-Feb-2022 07:14 | Ron Averes | Updated [Location] |
Corrections or additions? ... Edit this accident description
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