UK AAIB March 2012 (rotary)

[Hilico]

A109C in the cruise near Kew Bridge, birdstrike shatters left-hand windshield, P1 minor injuries as a result, P2 lands successfully: Air Accidents Investigation: Agusta A109C, N109TK (http://www.aaib.gov.uk/publications/bulletins/march_2012/agusta_a109c__n109tk.cfm)

Guimbal Cabri G2 develops high yaw rate just before alighting, fuel sloshing may have caused fuel starvation, engine stopped and a/c landed heavily: Air Accidents Investigation: Guimbal Cabri G2, G-UIMB (http://www.aaib.gov.uk/publications/bulletins/march_2012/guimbal_cabri_g2__g_uimb.cfm)

And last month, H500 experts will have been shaking their heads in despair at the AAIB's slapdash approach to accuracy - but fear not, they've realised: here (http://www.aaib.gov.uk/cms_resources.cfm?file=/McDonnell%20Douglas%20Helicopters%20Hughes%20369E%20G-KSWI%20Correction%2003-12.pdf)

Fly safe

Steve

PS Am I picking this back up now?

[VeeAny]

Steve,

Can you for the next month while I settle into a new role ? And I will do so from May onwards again.

I am also working on a new round of safety evenings for this year, as I hope to have more spare time than in the last 18 months.

Gary

[Hilico]

No problem. I would have PM'd you, but in another incident to be described in a couple of months:

PuT attempts to PM P1 but gets MRGB limits problem (Message Rejected, Gary's Blown (message) limits).

[RMK]

In the Cabri G2 incident, they’re talking about yawing to the left and needing more right pedal due to engine stopping. I assumed the G2 had a “clock-wise” rotor path like all Eurocopters. Is that not true?

[John R81]

Clockwise when viewed from above, it says in the report.

My Eurocopter yaws left in torque reaction, right foot to resist.

Keep repeating: "Turns to the right avoid a fright".


All fenestron tail aircraft (that I have have seen) have a large sail area in the tail compared to open blade design. If you allow a torque-related (left for me) yaw to develop then once the wind gets on to the tail one should expect a very strong increase of yaw rate. It takes a rapid boot-full to resist - in anticipation, preferably. Too slow or timid with your footwork, then around you go; and I understand that it can take a number of rotations to control - not so far happned to me, touch wood - so best that it not be allowed to develop at all.

Landing into wind (as it says in the report) then under-use of the right foot would lead to left yaw. The wind would increasingly press the tail back into line as more of the sail area is affected by the wind, which suggests that insufficient right foot is being used to prevent torque-related yaw even with the wind assistance on the tail. That all changes once the machine passes 9 o'clock to the wind as the assistance which the wind is giving on the sail area of the tail reduces, which the pilot experiences as increased yaw rate. Yaw rate will sharply increase one the machine is facing down-wind as the windis now helping the tail to go around, with maximum adverse tail-assistance being at 3 o'clock to the wind. There will be no positive tail-assistance until after the machine passes 12 o'clock again.

That's why, once developed, the machine will likely spin more than once before he pilot regains control.

Interesting that the manufacturer believes that fuel sloshing due to yaw can lead to engine failure due to fuel starvation. I would have hoped for a tank design that did not allow this to happen given that a fully-developed spin can take a number of rotations to bring under control. From the report, the pilot took the correct actions to stop the spin but ran out of time when the engine stopped.