NZ Seasprite accident report - ground reasonance

Anyone know how common ground resonance incidents are in helicopters in
general and SH-2s in particular?


www.nzherald.co.nz/index.cfm?ObjectID=10112184

see also http://www.nzdf.mil.nz/news/articles/2004/12/1206.html

Pilots censured on helicopter bungle

[Helicopters on RNZN ships are kind-of operated by the RNZAF, hence mixture
of Navy and Air Force references]



23.02.05



A Navy pilot and co-pilot responsible for a lashing bungle which damaged a
Seasprite helicopter during anti-terrorist patrols in the Gulf of Oman last
year have been censured, the Defence Force said yesterday.

The Seasprite, aboard the Navy frigate HMNZS Te Mana last May, was
incorrectly lashed to the deck, a court of inquiry found.

The helicopter was badly damaged by excessive vibration, known as ground
resonance, when its jet engine was started for a routine run.

Repair costs have been estimated at between $1.5-$3 million.

The Navy pilot and co-pilot involved in the incident had been censured, Air
Force spokesman Squadron Leader Ric Cullinane said.

"That essentially means a letter goes into their file and there will be
consequences for future employment, promotion or postings," he said. "But
there is the opportunity to show that it was a one-off incident." The
incident may eventually cost nearly $4 million, once additional costs of
delivering a replacement helicopter to the gulf and bringing the damaged
Seasprite home are accounted for.

The accident happened when the frigate was deployed as part of a
multi-national taskforce hunting for terrorists, sympathisers and illegal
cargoes in the gulf and the Arabian Sea.

Following court recommendations, the Navy and Royal New Zealand Air Force
are now developing new publications to highlight correct lashing procedures
and the dangers of ground resonance, and are reviewing training materials.

The Air Force magazine Insight said the Navy was fortunate the pilot was
unscathed and the aircraft was repairable.

"The majority of ground resonance events that have occurred on a Seasprite

have resulted in complete destruction of the aircraft." Mechanical problems
with the Air Force's five Seasprite helicopters in the past year reduced
training time and resulted in one mission sacrificing flight safety, Insight
said.

"On this occasion an aircraft, that was only rated for day visual flight
rules (VFR) flying, flew into the hours of darkness and the crew were
unaware that the anti-collision lights were unserviceable."

The Seasprites recorded 65 flight safety events (FSE) in 2004.

Eight incidents involved smoke and fumes, and five of those occurred in the
same helicopter, which took eight months to repair.

Numerous mechanical problems in the past year had meant training sorties had
not been completed in time and put pressure on instructors to conduct

exercises whenever possible, Insight said.

The Seasprites reported more incidents involving human factors than any

other squadron, "which is commendable, as all squadrons will have had a

number of incidents that went unreported", the magazine said.

A total of 357 FSEs were reported over 2004.


--
Errol Cavit | | "If I have to choose between my
country going under and England going under, I should want my country to go
under. For England is the bastion of us all." Dr.HV Evatt, Australian
Minister for External Affairs, New York, March 1942.

Errol Cavit wrote:
Anyone know how common ground resonance incidents are in helicopters in
general and SH-2s in particular?

Don't know much about the H-2, but on the H-60 there are a couple of
tiedown points just above and behind the cockpit doors. While the
rotors are turning you don't use these to chain the aircraft to the
ship, because the aircraft can get into ground resonsance that way.

I don't think ground resonsance incidents are very common. Common
causes might be a weak blade damper (like the shock absorber on your
car), combined with a hard landing that may "excite" one of the
blades to vibrate divergently. The way the aircraft is touching the
ground has a lot to do with it too- it will vibrate differently in
the air than on the ground when the wheels are on the deck or
depending on different tiedowns points being used. Possible
responses by the pilot could be immediately taking off again (to
break the connection to the ground) or immediately shutting down the
rotor system. The problem usually does not solve itself but instead
gets very bad in a matter of seconds.

That's it in a general terms. Each thing I said is not necessarily
true in every case of ground resonance.

If you want to understand it on a fundamental level, I think the
mathematical explanation is pretty advanced, way beyond my level
anyway