Dear Steven,

Your letter about the wet air filter element is interesting. This same factor was the cause of an accident down here in Otago during a particularly snowy period some years ago.

The pilot had been operating for most of the day as he recovered snow bound stock. This meant landing amongst snow disturbed by downwash for much of that time. Gradual induction of snow flakes caused the filter to become wetter and wetter until it totally collapsed. This starved the engine of air, causing an abrupt stop. The result was a crash.

The R22 used to have an alternate air source in the form of a sprung loaded flap on the bottom of the air box. RHC, for better or worse, has been not been incorporating this in the R22 for probably some 10 years.

The advent of the governor has been wonderful but it does bring up one major problem.

In 'the old days' before governors were mandatory the pilot was constantly rolling throttle on and off, especially when operating near the upper limit of MP. In doing so it was possible to feel when the throttle was at or near full input because it would be felt to come up against its stop. This early warning sign is now harder to detect because the governor is opening the throttle for you. It is not until a loss of RPM occurs that you realise the Helicopter is already in an overpitched state. You have to learn and adopt a new system of finding how much power (throttle travel remaining) you have available.

Here in the South Island where we frequently operate between 6 and 8000 feet. Sound judgement has to be used by the pilot. The way we check on the amount of throttle input remaining (or lack of it) is to give it a quick snap open to the stop (over riding the governor) and then back again. The pilot will immediately feel how much throttle travel remains.

There are so many times (especially on sling) when your attention or even your head is not in the cockpit. This method is a good one, it saves you having to continually duck your head inside to look at the gauges. Basically, it is taking you back to the days before the governor, giving you an early warning of approaching full throttle.

As you say in your letter there are a lot of reasons why the Helicopter may be down on power. In your case good on you for noticing a change from the normal and doing something about it.

Am still keen to see you instruction book when complete, with the view to using it in my business.

Kind regards

Simon Spencer Bower

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