Page 2 of 2

Re: Helicopter down, Leicester City FC

PostPosted:Thu Dec 06, 2018 2:33 pm
by chipmeisterc
https://assets.publishing.service.gov.u ... vhpeaVaKVw

"The evidence gathered to date shows that the loss of control of the helicopter resulted
from the tail rotor actuator control shaft becoming disconnected from the actuator lever
mechanism. Disconnection of the control shaft from the lever prevented the feedback
mechanism for the tail rotor actuator from operating and the tail rotor actuator from
responding to yaw control inputs. Loss of the feedback mechanism rendered the yaw
stops ineffective, allowing the tail rotor actuator to continue changing the pitch of the
tail rotor blades until they reached the physical limit of their travel. This resulted in an
uncontrollable right yaw.
Sufficient force and torque had been applied to the castellated nut on the actuator end of
the control shaft to friction weld it to the pin carrier and to shear the installed split pin. The
observed condition of the duplex bearing and the increased torque load on the castellated
nut that remained on the spider end of the shaft is consistent with rotation of the tail rotor
actuator control shaft. Whilst the shaft was rotating and a yaw control input was applied, the
shaft “unscrewed” from the nut, disconnecting the shaft from the actuator lever mechanism,
and causing the nut to become welded to the pin carrier. "

Re: Helicopter down, Leicester City FC

PostPosted:Wed Sep 06, 2023 10:22 am
by kanga
BBC gist of final AAIB report, with AAIB animation:

https://www.bbc.co.uk/news/uk-england-l ... e-66716572

"Pilot could do 'very little' to stop Leicester City helicopter crash"

'..The Air Accidents Investigation Branch (AAIB)'s final report said a tail rotor bearing seized, which in turn caused the crash.

The AAIB said the crash was "inevitable" after a sequence of mechanical failures...'

Re: Helicopter down, Leicester City FC

PostPosted:Wed Sep 06, 2023 12:54 pm
by kilburnflyer
If I was a heli -pilot on that type I would like to know why something so critical failed with such catastrophic results on a modern design within the promulgated inspection period.

Re: Helicopter down, Leicester City FC

PostPosted:Wed Sep 06, 2023 2:32 pm
by A4 Pacific
If I was a heli -pilot on that type I would like to know why something so critical failed with such catastrophic results on a modern design within the promulgated inspection period.


You can be confident the families of those on board will seek answers to the very same question.

Design, manufacture, maintenance or usage?

Re: Helicopter down, Leicester City FC

PostPosted:Wed Sep 06, 2023 4:50 pm
by FredFly
To add some detail to the article:

With counter-clockwise rotating main rotor, engine torque will cause the fuselage to rotate clockwise (to the right); the tail rotor exerts force to left of tail boom to counteract/balance forces. The AW169 has a counter-clockwise rotating main rotor and “Tractor/Puller” type tail rotor (i.e.. it’s blowing air to the left even though mounted on right) as opposed to more traditional “Pusher” type TR.

The tail rotor of a helicopter uses circa 10% of the engines power; the AW169 has two 1000SHP engines, so this tail rotor had circa 200SHP going to it.

When the controls failed/disconnected, it did not just fail to provide antitorque but failed “full over” in opposite direction (spinning the fuselage even faster). Loss of TR thrust will cause the aircraft to yaw to the right; this was compounded by the tail rotor also yawing the aircraft to the right at full pitch with circa 200SHP.

This was the worst case for control. The pilot would been in a better situation if they had actually lost the tail rotor or even the whole TR gearbox/assembly.

Re: Helicopter down, Leicester City FC

PostPosted:Wed Sep 06, 2023 7:58 pm
by Boxkite
FredFly wrote:The tail rotor of a helicopter uses circa 10% of the engines power; the AW169 has two 1000SHP engines, so this tail rotor had circa 200SHP going to it.

When the controls failed/disconnected, it did not just fail to provide antitorque but failed “full over” in opposite direction (spinning the fuselage even faster). Loss of TR thrust will cause the aircraft to yaw to the right; this was compounded by the tail rotor also yawing the aircraft to the right at full pitch with circa 200SHP.

If both engines were at max ouput at that time....

Re: Helicopter down, Leicester City FC

PostPosted:Wed Sep 06, 2023 9:31 pm
by A4 Pacific
If both engines were at max ouput at that time....


I suspect in the early stages of the failure that may well have been what was occurring? They received a “Low Rotor RPM” warning. I can only presume that may have been due to the excessive pitch on the tail rotor dragging down the main rotor RPM despite max output from the powerplants? Clearly soon after that, the pilot lowered the collective which likely reduced the required power output from the engines without doing anything to resolve the problem, other than preserving rotor RPM to cushion the inevitable arrival.

They were all extremely unlucky in the final moments. The pilot appears to have achieved a ‘grounding’ that in slightly different circumstances, should have been survivable by at least some of those on board?