AAIB - Westland WASP G-KAXT
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AAIB - Westland WASP G-KAXT
Did a quick search and couldn't find reference to this. G-KAXT Westland Wasp Loss of collective pitch control resulting in a forced landing, Bishopstone, near Salisbury, Wiltshire, 23 September 2016.
With the helicopter straight and level at approximately 1,150 ft, the pilot felt vibration through the collective lever. The vibration ceased after two or three seconds. Approaching higher ground, the pilot pulled up on the collective lever but the helicopter did not respond. He lowered the lever and again, there was no response. Faced with a loss of collective pitch control, the pilot made a precautionary landing.
The collective pitch control rod in the main rotor gearbox had broken. The control rod failure was secondary to a universal joint failure that had occurred in the cyclic control circuit due to lack of lubrication and a build-up of corrosion deposits. That was a result of the design of the lubrication system; fill a reservoir during overhaul of the gearbox when changing the universal joint. The overhaul in this case was 600 hours, and with anticipated military use of 200 hrs per year that would be 3 years. After retirement, the machine had low hrs and so over 20 years the 600 hrs had not been achieved - the universal joint lubricating oil was exhausted from the reservoir and the joint ran "dry" until it failed.
Just goes to show; you have to understand exactly how the thing is built and what it means to depart from the "expected use" which the maintenance schedule is designed around.
With the helicopter straight and level at approximately 1,150 ft, the pilot felt vibration through the collective lever. The vibration ceased after two or three seconds. Approaching higher ground, the pilot pulled up on the collective lever but the helicopter did not respond. He lowered the lever and again, there was no response. Faced with a loss of collective pitch control, the pilot made a precautionary landing.
The collective pitch control rod in the main rotor gearbox had broken. The control rod failure was secondary to a universal joint failure that had occurred in the cyclic control circuit due to lack of lubrication and a build-up of corrosion deposits. That was a result of the design of the lubrication system; fill a reservoir during overhaul of the gearbox when changing the universal joint. The overhaul in this case was 600 hours, and with anticipated military use of 200 hrs per year that would be 3 years. After retirement, the machine had low hrs and so over 20 years the 600 hrs had not been achieved - the universal joint lubricating oil was exhausted from the reservoir and the joint ran "dry" until it failed.
Just goes to show; you have to understand exactly how the thing is built and what it means to depart from the "expected use" which the maintenance schedule is designed around.
common thread here after reading report on the shoreham hunter and now hydraulic pump issues with the sea vixen which we haven't heard detail in terms of last overhaul yet. problem is identifying potential problem areas on a type long out of service and finding the expertise to identify problems. Also worrying is this is a relatively simple type and this could easily have ended up with a worse outcome. Hopefully we will still see these continue to fly !
Same cause as a fatal piston Provost accident a few years ago - maintenance being done on hours not calendar as never envisaged an issue when in service. It's hard to imagine a big of common sense would not identify this though!
