Helicopter down outside Leicester City Football Club
As stated in my post earlier in this thread, I am not a pilot. I am however, a groundsman, and have worked in stadium environments on and off for many years. What I can tell you is that if standard post match practices were carried out (they may well not have been, given the circumstances), there is a very good chance that any missing components would have been found, if they were on the pitch itself.
Immediately following matches at this level, pitches are effectively 'hoovered' with mowers to remove debris - this debris includes organic debris i'e., tufts of grass etc, and also objects thrown onto the pitch - coins is the common issue in this respect. If a nut, or other component was on the pitch, it would have been found during the post match 'clean up, or failing that, during the next cut as the mower blades would 'find' it.
I suspect however that all pitch maintenance activities would have been suspended immediately given the nature and location of the incident. That said, if there were any components on the pitch, they would most definitely have been found by now.
Immediately following matches at this level, pitches are effectively 'hoovered' with mowers to remove debris - this debris includes organic debris i'e., tufts of grass etc, and also objects thrown onto the pitch - coins is the common issue in this respect. If a nut, or other component was on the pitch, it would have been found during the post match 'clean up, or failing that, during the next cut as the mower blades would 'find' it.
I suspect however that all pitch maintenance activities would have been suspended immediately given the nature and location of the incident. That said, if there were any components on the pitch, they would most definitely have been found by now.
dont make the assumption, or imply that i did, that it fell out into the grass. more than likely it stayed within the cowlings, at least until the crash anyways
Here is a question.
Can someone explain the process / thinking around the AD? In so much that the commentary for the reason of the AD says:-
What I don't understand is the aircraft crashes almost 2 weeks ago. If the AD is truly a precautionary element what prompts the thinking of this 2 weeks later? Surely either its a precaution thinking out loud type AD, in which case why not flag earlier? Or they are concerned about something they have seen more recently, in which case why not just say?? It just seems bizarre.
Can someone explain the process / thinking around the AD? In so much that the commentary for the reason of the AD says:-
Reason: An accident occurred on an AW169 helicopter, the root cause of which has not been identified and the technical investigation is still ongoing. While the helicopter was on a take-off phase at low forward speed, a loss of yaw control has been observed.
As a precautionary measure, Leonardo issued ASB 169-120 for AW169 helicopters to provide inspection instructions to check correct installation of the tail rotor (TR) servo-actuator
As a precautionary measure, Leonardo issued ASB 169-120 for AW169 helicopters to provide inspection instructions to check correct installation of the tail rotor (TR) servo-actuator
It would be incredible if this isn't off the back of something seen or suspected and so why it can't be said more plainly - or indeed co-ordinated via the AAIB goodness knows... Hey Ho.
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Most likely is that they suspect a fault in the feedback link but may not know exactly what at this stage.
Hard to fathom how pin and lockwire could be missed on assembly so might be a failure.
Here is one scenario: If the lockwire was incorrectly installed could it eventually wear into the locking pin, possibly on the head side?
.
It is a slow news week....
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I think TR blades tend towards zero pitch when uncontrolled. Gazelle definitely did in manual. Lynx as well, albeit with a powerful spring bias unit? Sea King? Is it generic or type specific?
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Thanks for the input.
What is the approximate full stroke of the actuator relative to the washer thickness? Would the missing washer offset on null and full stroke positions be subtle/adjustable at some other point or clearly way out? In any case it is hard to fathom leaving the factory that way or with missing lock means.
What is the approximate full stroke of the actuator relative to the washer thickness? Would the missing washer offset on null and full stroke positions be subtle/adjustable at some other point or clearly way out? In any case it is hard to fathom leaving the factory that way or with missing lock means.
I don’t think you would be able to adjust the input mechanism to account for the missing component and the result would be a setting should be far enough out to be identified and rectified.
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Yes, the servo actuator is static but I think there will be some torque transmitted down the control rod as the attachment (bearing assembly?) from the control rod to rotor pitch mechanism will not have zero friction.
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CAA PAPER 2003/1
Helicopter Tail Rotor Failures is well worth a read. Here are some extracts.
There are two major types of TRF:
a) A TR drive failure (TRDF) is a failure within the TR drive system with consequent
(usually total) loss of TR thrust. Example causes are internal fatigue or external
impact resulting in a broken drive shaft.
b) A TR control failure (TRCF) is a failure within the TR control system such that
normal pilot control of TR thrust has been partially or totally lost. Example causes
are internal wear or external impact resulting in a severed control cable. The
resultant TR applied pitch, or power, could be free to fluctuate, or may be fixed
anywhere between high pitch (HP) or low pitch (LP) setting, including that of the
current trim pitch (TP).
Both of these TRFs are time critical emergencies. The pilot has to identify and
diagnose the TRF type and react with the correct control strategy within a few
seconds (or less), to prevent the aircraft departing into an uncontrollable flight state.
Even if the pilot recovers from the initial transients, yaw (pedal) control will have been
lost and the ability to manoeuvre safely and carry out a safe landing will have been
significantly degraded. The TR and its drive and control systems are clearly flight
critical components and should be designed so that their probability of failure is
‘extremely remote’. The airworthiness design requirements for UK military and civil
aircraft define ‘extremely remote’ as being less than 10-6 [1] and between 10-7 and
10-9 [2,3] per flight hour respectively.
Recovery from the failure transient
For TRDFs, and TRCFs where the post-failure pitch angle of the TR blades is different
from the pre-failure trim position, the immediate effect is a yaw response. That is, (for
anticlockwise main rotors), nose to starboard following a TRDF or LP TRCF, and nose
to port following a HP TRCF. The level of initial yaw acceleration will depend on the
nature of the failure, and the level of yaw rate and attitude build-up will depend on the
forward speed. In hover, an unchecked TRDF will result in the yawing moment from
the main rotor torque reaction spinning the fuselage at rates in excess of 100° sec-1,
perhaps even as high as 150-200° sec-1. Typically, the higher the forward speed, the
lower the yaw rate and attitude excursion as any natural directional stability of the
aircraft will tend to reduce the severity of the motion. However, this is only true up to
some value of sideslip, beyond which it is possible that directional stability can
reverse, resulting in increased yaw rate and attitude excursions. Evidence from the
Lynx TRF AFS trial [5] suggests that the ability of the pilot to successfully manage a
forward flight failure is strongly related to the extent of the initial yaw/sideslip
transient. If this exceeds 90°, then the pilot is unlikely to be able to recover, as the
flight control problem is exacerbated by disorientation; if the yaw rate reduces to zero
below about 30° yaw angle, then the pilot has a much greater chance of recovering
from the failure. Accompanying the yaw excursions will be pitch and roll motion,
which can further increase the risk of disorientation. An additional effect of any roll
attitude transient is an increase in the main rotor disc angle of incidence, leading to
an increased risk of the rotor over-speeding as the pilot reduces main rotor collective
to contain the effects of the failure. The extent of the attitude excursions depends on
the aerodynamic design characteristics of the fuselage and vertical stabiliser, the
resulting directional stability, the type of attitude stabilisation present in the flight
control system and the pilot’s control actions
Helicopter Tail Rotor Failures is well worth a read. Here are some extracts.
There are two major types of TRF:
a) A TR drive failure (TRDF) is a failure within the TR drive system with consequent
(usually total) loss of TR thrust. Example causes are internal fatigue or external
impact resulting in a broken drive shaft.
b) A TR control failure (TRCF) is a failure within the TR control system such that
normal pilot control of TR thrust has been partially or totally lost. Example causes
are internal wear or external impact resulting in a severed control cable. The
resultant TR applied pitch, or power, could be free to fluctuate, or may be fixed
anywhere between high pitch (HP) or low pitch (LP) setting, including that of the
current trim pitch (TP).
Both of these TRFs are time critical emergencies. The pilot has to identify and
diagnose the TRF type and react with the correct control strategy within a few
seconds (or less), to prevent the aircraft departing into an uncontrollable flight state.
Even if the pilot recovers from the initial transients, yaw (pedal) control will have been
lost and the ability to manoeuvre safely and carry out a safe landing will have been
significantly degraded. The TR and its drive and control systems are clearly flight
critical components and should be designed so that their probability of failure is
‘extremely remote’. The airworthiness design requirements for UK military and civil
aircraft define ‘extremely remote’ as being less than 10-6 [1] and between 10-7 and
10-9 [2,3] per flight hour respectively.
Recovery from the failure transient
For TRDFs, and TRCFs where the post-failure pitch angle of the TR blades is different
from the pre-failure trim position, the immediate effect is a yaw response. That is, (for
anticlockwise main rotors), nose to starboard following a TRDF or LP TRCF, and nose
to port following a HP TRCF. The level of initial yaw acceleration will depend on the
nature of the failure, and the level of yaw rate and attitude build-up will depend on the
forward speed. In hover, an unchecked TRDF will result in the yawing moment from
the main rotor torque reaction spinning the fuselage at rates in excess of 100° sec-1,
perhaps even as high as 150-200° sec-1. Typically, the higher the forward speed, the
lower the yaw rate and attitude excursion as any natural directional stability of the
aircraft will tend to reduce the severity of the motion. However, this is only true up to
some value of sideslip, beyond which it is possible that directional stability can
reverse, resulting in increased yaw rate and attitude excursions. Evidence from the
Lynx TRF AFS trial [5] suggests that the ability of the pilot to successfully manage a
forward flight failure is strongly related to the extent of the initial yaw/sideslip
transient. If this exceeds 90°, then the pilot is unlikely to be able to recover, as the
flight control problem is exacerbated by disorientation; if the yaw rate reduces to zero
below about 30° yaw angle, then the pilot has a much greater chance of recovering
from the failure. Accompanying the yaw excursions will be pitch and roll motion,
which can further increase the risk of disorientation. An additional effect of any roll
attitude transient is an increase in the main rotor disc angle of incidence, leading to
an increased risk of the rotor over-speeding as the pilot reduces main rotor collective
to contain the effects of the failure. The extent of the attitude excursions depends on
the aerodynamic design characteristics of the fuselage and vertical stabiliser, the
resulting directional stability, the type of attitude stabilisation present in the flight
control system and the pilot’s control actions
Chronus, #3, loss of tail rotor blade ,followed milliseconds later by loss of other blade(s),and probably the gearbox.. The C of G of the a/c will move to somewhere beyond the nose of the a/c ....
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As a former helicopter pilot I experienced three total engine failures in single engine helicopters and three lucky autorotations that saved the day for my pax, me and the company. Most of my helicopter time though is logged in twin engine helicopters, one of which also gave me an engine failure, but that was in level flight and therefore nothing of interest..
With Occam's razor in mind I got to my very own simplified conclusion that this accident started with a tail rotor failure that turned out catastrophic due to no visual recovery in the blurry video. The helicopter’s counter rotation and the engine sound made me think the helicopter descended with high power and high collective all the way to the ground.. The shape of the tail rotor blades on the downed helicopter made me also think that the helicopter hit the ground with the TR not spinning at all due to a TR drive failure… Why wasn’t the pilots able to lower the collective?
With Occam's razor in mind I got to my very own simplified conclusion that this accident started with a tail rotor failure that turned out catastrophic due to no visual recovery in the blurry video. The helicopter’s counter rotation and the engine sound made me think the helicopter descended with high power and high collective all the way to the ground.. The shape of the tail rotor blades on the downed helicopter made me also think that the helicopter hit the ground with the TR not spinning at all due to a TR drive failure… Why wasn’t the pilots able to lower the collective?
Slap,
That was some British understatement being used.
When you lose the Tail Rotor Blades, Gearbox, and associated items from the very rear of the helicopter....the CG shift is forward...and very significant....causing a strong pitching movement that might exceed the ability of the flight controls to compensate for and thus cause the loss of the aircraft.
That was some British understatement being used.
When you lose the Tail Rotor Blades, Gearbox, and associated items from the very rear of the helicopter....the CG shift is forward...and very significant....causing a strong pitching movement that might exceed the ability of the flight controls to compensate for and thus cause the loss of the aircraft.
Yeah that would be fair but what evidence? The video footage was available almost instantly and so now evidence surely means physical evidence from the accident aircraft or of prior events that have been caught prior to an accident with other in service aircraft. It can't be the former if the narrative around the AD is faithful and if its the latter does that take a week to get out with the commitment of intelligent minds?
It would be incredible if this isn't off the back of something seen or suspected and so why it can't be said more plainly - or indeed co-ordinated via the AAIB goodness knows... Hey Ho.
It would be incredible if this isn't off the back of something seen or suspected and so why it can't be said more plainly - or indeed co-ordinated via the AAIB goodness knows... Hey Ho.
The investigation is probably far from over and as far as I know no one would release informations until all data has been analysed.
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As a former helicopter pilot I experienced three total engine failures in single engine helicopters and three lucky autorotations that saved the day for my pax, me and the company. Most of my helicopter time though is logged in twin engine helicopters, one of which also gave me an engine failure, but that was in level flight and therefore nothing of interest..
With Occam's razor in mind I got to my very own simplified conclusion that this accident started with a tail rotor failure that turned out catastrophic due to no visual recovery in the blurry video. The helicopter’s counter rotation and the engine sound made me think the helicopter descended with high power and high collective all the way to the ground.. The shape of the tail rotor blades on the downed helicopter made me also think that the helicopter hit the ground with the TR not spinning at all due to a TR drive failure… Why wasn’t the pilots able to lower the collective?
With Occam's razor in mind I got to my very own simplified conclusion that this accident started with a tail rotor failure that turned out catastrophic due to no visual recovery in the blurry video. The helicopter’s counter rotation and the engine sound made me think the helicopter descended with high power and high collective all the way to the ground.. The shape of the tail rotor blades on the downed helicopter made me also think that the helicopter hit the ground with the TR not spinning at all due to a TR drive failure… Why wasn’t the pilots able to lower the collective?
My guess would be because it was a time critical event.
Factors are : Height above ground coupled with the likelihood of occurence at critical moment of transit to forward flight, size of helicopter, twin engines, high rotation speed following TRFand location of site.
Any chance of succesful recovery would have entailed almost instant recognition of TRF, immediate power reduction and simultaneous pitch down for immediate descent and autorotation, which would involve a high ROD and require favourable terrain below. Might be survivable at low height but not so at the sort of height involved in this instance.
I would readily admit I know little about rotary wing, but I understand that they are far less forgiving than their fixed wing sisters. One thing in common must be that with the vertical stab gone on a fixed wing it also spells curtain time, but as in the cases of the JAL123 747 which managed slightly better than AA 587 they seem to keep going for a little longer before the inevitable. With rotary wing the equivalent of no TR means in no time at all the machine assumes the characteristics of a dandelion strung to a brick.
I really don`t think even the most accomplished pilot could have pulled it off. It would have been a far greater miracle than the Hudson one if they had, would be my humble view.
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Chronus: Is this because of loss of yaw stability or the shift in CG?
Jag,you will lose your stability in yaw,coupled with the C OF G change; you might be able to crowd pax into the back to restore/mitigate the CG PROBLEM.The a/c if disturbed in yaw or roll will probably start Dutch -rolling which will require a lot of handling skills,especially during any configuration changes,and approach/landing....or may not.. A B52 lost it`s fin/rudder and landed safely-see u-tube..
Slap,in my case of t/r and gearbox departure ,the change of CG was about 3" forward of the Fwd limit,`past my nose, anyway`!! The stick has reached the back-stop ,and the a/c has changed direction by about 50-60*;entering autorotation and chopped the engine leads to a further pitch down ,but there is a `pimple` of a hilltop with cleared scrub that we are pointing at.
To flare requires another quick fwd stick and back again with lever,as it`s also uphill,but at zero groundspeed.Landed upright,but burst a main tyre on a treestump.. ...There is a pic on `Rotorheads around the World-views from cockpit(not video) ,page 15....
Slap,in my case of t/r and gearbox departure ,the change of CG was about 3" forward of the Fwd limit,`past my nose, anyway`!! The stick has reached the back-stop ,and the a/c has changed direction by about 50-60*;entering autorotation and chopped the engine leads to a further pitch down ,but there is a `pimple` of a hilltop with cleared scrub that we are pointing at.
To flare requires another quick fwd stick and back again with lever,as it`s also uphill,but at zero groundspeed.Landed upright,but burst a main tyre on a treestump.. ...There is a pic on `Rotorheads around the World-views from cockpit(not video) ,page 15....
Slap,
That was some British understatement being used.
When you lose the Tail Rotor Blades, Gearbox, and associated items from the very rear of the helicopter....the CG shift is forward...and very significant....causing a strong pitching movement that might exceed the ability of the flight controls to compensate for and thus cause the loss of the aircraft.
That was some British understatement being used.
When you lose the Tail Rotor Blades, Gearbox, and associated items from the very rear of the helicopter....the CG shift is forward...and very significant....causing a strong pitching movement that might exceed the ability of the flight controls to compensate for and thus cause the loss of the aircraft.
You can PM me and we can talk the details.
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Why look for a TR failure ?
Statistically there are many more accidents due to unanticipated yaw -- so poorly named as LTE -- than due to TR failures. Looking at the initial yaw, there is no abrupt acceleration. If it is a TR failure, I guess you have to look for a very progressive failure...
AAIB investigations will say it.
AAIB investigations will say it.
