Seasprite Court Of Inquiry: Summary Of Findings

Questions and Answers for Media Release dated 6 December 04

What is Ground Resonance?

Ground resonance is a phenomenon that occurs in helicopters like the Seasprite with a fully articulated rotor-head, a dampened undercarriage and, usually, on helicopters with inflatable tyres. Ground resonance occurs when the precise centre of gravity of the turning rotor disc is displaced from the precise centre of rotation. A common analogy is a child’s spinning top – at low rpm the centre of gravity and centre of rotation are not aligned and the top develops a “wobble”.

Helicopters are designed to provide mutual dampening between the main rotor and the undercarriage.

What happened during the accident?

On 22 May 2004, HMNZS Te Mana was conducting routine patrol operations in the Gulf of Oman. A flying operation was scheduled for that morning in support of the operation, with a maintenance ground run required before launch.

The ground run was required to check an oil cooler pipeline that had been replaced earlier. The check required running the number one engine and engaging the rotors. The aircraft was fully lashed to the deck using chain lashings, two of which were attached to the high points immediately beneath both engine nacelles.

During rotor engagement the pilot noticed slightly rougher than usual airframe oscillations. The airframe oscillation quickly developed into ground resonance and became more severe. As soon as the pilot had identified the ground resonance condition he shut the aircraft down.

Damage involved the starboard high point lashing had parted causing damage to the starboard window and door, and damage to the undercarriage on both sides with associated creasing in the skin.

What is the cost of the repair?

The estimated cost to repair the Seasprite is between NZ$1.5 and 3.0 million. It is estimated that the repairs will be completed by the end of January 2005.

What action has been taken to prevent similar occurrences in the future?

The recommendations of the Court of Inquiry are currently being implemented by the responsible agencies within the Navy and Air Force. A number of recommendations were made to improve technical and aircrew publications to better highlight the correct chain lashing procedures, and the dangers of ground resonance. Training syllabi have also been reviewed to ensure adequate instruction on the causes and consequences of ground resonance is provided to all aircrew, maintenance crew, and flight deck officers.

What action has been taken in respect of the personnel involved?

The aircrew involved have been censured on their performance.

ENDS

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