February's AAIB - helis and cables

[Hilico]

I don't recall seeing either of these at the time - thankfully (and incredibly, in one case) there was no loss of life or even serious injury. Both in Scotland for some reason.

Gazelle strikes cables, low sun obscuring visibility - this one. (http://www.dft.gov.uk/stellent/groups/dft_avsafety/documents/page/dft_avsafety_027264.hcsp)

AS350 notices cables from a little way away but commander unsure whether he missed them - this one. (http://www.dft.gov.uk/stellent/groups/dft_avsafety/documents/page/dft_avsafety_027263.hcsp)

[pilotwolf]

The Gazelle incident was discussed on here - believe it was about the same time as the ex - rally driver pranged his machine- think it was within that thread...

PW

[The Nr Fairy]

Something about the G-NIOL report (http://www.dft.gov.uk/stellent/groups/dft_avsafety/documents/page/dft_avsafety_027265.hcsp) is puzzling me.

The pilot also made a verbal observation that during the ground slide he felt that he had tail rotor control; this suggests that the rotor system was under power at that time

Now, correct me if I'm wrong, but the drive system - assuming no mechanical failures - ensures that if the main rotor is turning, the tail rotor is driven as well, power or not ? The only difference is yaw authority, being dependent on RRPM, will reduce as the main rotor slows.

:confused:

[pilotwolf]

Also...

As autorotation was established, he raised the collective slightly to reduce rotor speed and noticed that the engine was still running.

Why had he considered it had stopped? Nothing in the report suggests this except the decaying rpm. A quick check of oil pressure, manifold pressure and lack of 'no noise' would have given him clues surely? Maybe the situation overuled the brain?

He tried to execute a powered recovery by opening the throttle, noticing that the engine RPM needle came up to meet the rotor RPM, but it seemed unable to output any power to the rotors.

Maybe I m being silly but I don't understand this statement. Do they mean the rate of descent didn't decrease? Which would seem to suggest the settling with power theory. But the report says he raised the collective, add power after this point.

Again I may be looking at this from the wrong angle, (and with hindsight and approaching twice his number of hours) but if he hadn't rolled the throttle off to enter auto and just lower the collective to regain rpm the accident would have been less likely to have happended....

As for the (lack of) yaw problem maybe he wasn't able to keep it straight and that's why he felt he had no authority until it was on the ground. Also if I recall correctly it doesn't require much decrease in rpm to seriously reduce the tail rotor authority due to the high gearing. Something like 100rpm decrease in MR = 600 rpm decrease in TR...

Written before the day's first cup of tea so please forgive silly errors! ;)

[Shawn Coyle]

pilotwolf
Just like your post was written before the first cup of tea, one should take pilot statements with a large grain of salt- without a lot of training, it is very difficult to say exactly what you mean (I know, because I have to teach student test pilots to do exactly this, and I go through red pens quickly).
So, don't try to split out what the pilot said happened in a lot of pilot reports- we all get things wrong even when we are observing in full awareness of what is going to happen, and when something unexpected happens, the powers of observation are among the first things to go.