Helicopter down outside Leicester City Football Club
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Only the extension/retraction of the pitch change shaft. It would appear once a full pedal input was made the feedback lever link disconnected itself from the pitch change shaft. It happened within 45 secs of take off and from the video, appeared to fail at the first significant yaw input. Was the nut in place before it lifted?
As to this thread being full of "absolute bo££ox", IMHO I'd echo the point made earlier (which I can't now find) that for inexperienced pilots (such as me), the amount of insight from those who are far more knowledgeable has a value that far outweighs the obvious nonsense - which we can easily choose to skip.
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[QUOTE=noooby;10303760]Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.
I remember delivering a new EC135 T1 to a new owner, during a walk round of the aircraft with him he commented that the tail rotor seemed to be missing a fairing, I pointed out it never had one, to facilitate preflight inspection and daily maintenance. 2 years later I flew the new P2 version that did have a fairing covering the important bits. Being old school I'd rather be able to cast an eye and a torch over the Tail rotor components, the P2 looked tidier but I always thought it was an improvement that actually made things worse.
My only accident was a tail rotor drive failure, thankfully only from a high hover taxi, due to servicing error. The intermediate gearbox came off the tailboom with most of the drive shafts and tail fairings. I'd already completed 4 ground runs to track and vibe the Tail rotor which had had components replaced. The 5 bolts holding the shaft to the IGB had been replaced but the engineer had not replaced the nuts. The supervisor signed off the job and secured the fairings, from that point on the aircraft was doomed. I felt a slight vibe through the pedals for around 2 seconds before it went bang just as I moved forward after the post take off checks. Thankfully the non handling pilot got the ECLs back just as I got the collective down and we had rotated through a full 360 turn.
The missing nuts were still on the bench in the hangar, I've had a very wary approach to tail rotors ever since, particularly when they've been tinkered with!
I remember delivering a new EC135 T1 to a new owner, during a walk round of the aircraft with him he commented that the tail rotor seemed to be missing a fairing, I pointed out it never had one, to facilitate preflight inspection and daily maintenance. 2 years later I flew the new P2 version that did have a fairing covering the important bits. Being old school I'd rather be able to cast an eye and a torch over the Tail rotor components, the P2 looked tidier but I always thought it was an improvement that actually made things worse.
My only accident was a tail rotor drive failure, thankfully only from a high hover taxi, due to servicing error. The intermediate gearbox came off the tailboom with most of the drive shafts and tail fairings. I'd already completed 4 ground runs to track and vibe the Tail rotor which had had components replaced. The 5 bolts holding the shaft to the IGB had been replaced but the engineer had not replaced the nuts. The supervisor signed off the job and secured the fairings, from that point on the aircraft was doomed. I felt a slight vibe through the pedals for around 2 seconds before it went bang just as I moved forward after the post take off checks. Thankfully the non handling pilot got the ECLs back just as I got the collective down and we had rotated through a full 360 turn.
The missing nuts were still on the bench in the hangar, I've had a very wary approach to tail rotors ever since, particularly when they've been tinkered with!
Art....‘‘twas not the tail rotor that let you down!
Sycamore, the TR is duplex hydraulic. It is controlled with a single push-pull cable. Unlike previous Leo machines that have relied on control tubes. Hydraulics cannot be selected off as the aircraft cannot be flown without hydraulics.
I know as much as any 169 operator who asks the right questions
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First off, I'm just relaying what Leonardo is telling the operators when they ask about this SB. That the AAIB have not (as yet) given them any info about possible or probable causes of this accident.
Sycamore, the TR is duplex hydraulic. It is controlled with a single push-pull cable. Unlike previous Leo machines that have relied on control tubes. Hydraulics cannot be selected off as the aircraft cannot be flown without hydraulics.
I know as much as any 169 operator who asks the right questions
Sycamore, the TR is duplex hydraulic. It is controlled with a single push-pull cable. Unlike previous Leo machines that have relied on control tubes. Hydraulics cannot be selected off as the aircraft cannot be flown without hydraulics.
I know as much as any 169 operator who asks the right questions
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.
Not discernible from the drawing but appears that the shoulder the washer sits on is probably just a bit larger than the hole in the hinge bracket (90). Lack of washer would allow the system to operate normally but might cause high stress on the hinge bracket leading to a fracture. Even without a fracture it could dig a hole in the hinge bracket resulting in play that could cause other issues such as the nut being loose which in turn could cause other damage.
[QUOTE=MurphyWasRight;10304564]From the picture it seems improbable that both locking means were missing/misinstalled.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.
I have no experience on this helicopter type (but 43 years on many others).
In most mechanical assembly situations a washer is placed "under" a nut, and looks "correctly assembled" when inspected, but it is the opposite in this case.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.
I have no experience on this helicopter type (but 43 years on many others).
In most mechanical assembly situations a washer is placed "under" a nut, and looks "correctly assembled" when inspected, but it is the opposite in this case.
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E. DESCRIPTION
Following an in service event, this Service Bulletin requires an urgent check of the proper installation and functionality of the Tail Rotor servo-actuator feedback lever installation and interface on the back end of the component.
Incorrect installation may lead to loss of Tail Rotor control which, depending on the flight condition, could lead to loss of control of the aircraft.
Feedback on the compliance to this Service Bulletin is required
3. Perform a visual inspection of the input lever of the TR servo-actuator:
3.1 With reference to Figure 1 and Figure 2 perform an in situ inspection of the nut (60), the cotter pin (50), the lock-wire and the hinge bracket element (90) connected to the lever feedback link (110) for condition and absence of damage.
3.2 Check the connection elements of the input lever (110) of the TR servo-actuator taking particular care on the lever feedback link.
Murphy, there are possibilities as you suggest. The wording of the SD is perhaps not ideal and certainly doesn't detail any specific potential fault or assembly mistake, and maybe that is for a reason; the intention being to ensure that all ships have the components in place and correctly installed in good condition, not to support speculation about actual cause of the accident. However the SD also doesn't mention that washer with the other components.
Nothing to do but wait...
Following an in service event, this Service Bulletin requires an urgent check of the proper installation and functionality of the Tail Rotor servo-actuator feedback lever installation and interface on the back end of the component.
Incorrect installation may lead to loss of Tail Rotor control which, depending on the flight condition, could lead to loss of control of the aircraft.
Feedback on the compliance to this Service Bulletin is required
3. Perform a visual inspection of the input lever of the TR servo-actuator:
3.1 With reference to Figure 1 and Figure 2 perform an in situ inspection of the nut (60), the cotter pin (50), the lock-wire and the hinge bracket element (90) connected to the lever feedback link (110) for condition and absence of damage.
3.2 Check the connection elements of the input lever (110) of the TR servo-actuator taking particular care on the lever feedback link.
Murphy, there are possibilities as you suggest. The wording of the SD is perhaps not ideal and certainly doesn't detail any specific potential fault or assembly mistake, and maybe that is for a reason; the intention being to ensure that all ships have the components in place and correctly installed in good condition, not to support speculation about actual cause of the accident. However the SD also doesn't mention that washer with the other components.
Nothing to do but wait...
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Interesting. As stated in the EAD, perhaps simply a precautionary measure based on what was observed in the accident. It would appear there is though, a way in which the mechanism can be incorrectly installed/assembled that has been either observed or imagined and is causing concern. Of course this may yet not apply in the case of this recent accident.
you can guarantee they found a missing nut on the accident helicopter at this point.
what they cant guarantee yet is if it was an isolated incident or not. Hence the SB and AD.
this is the data gathering stage where they find out if it's a widespread issue or not.
Ive been reading others posts about the two stages of locking. This is a must on any flight control. Dont forget though that they are only safety nets to the initial locking, which is the correct torque on the nut. Continual inspections offer the final net of safety.
In essence what I am saying is there was 4 failures here.
The torque was lost/incorrect or was never applied, allowing the nut to un-thread.
either faulty cotterpin/lockwire, or missing cotterpin/lockwire the failure was just a matter of time.
and the 4th, the inspections, didn't catch the impending loss.
Personally I think the loss of the nut would have happened quickly once torque was lost and the safety features failed to retain it.
what they cant guarantee yet is if it was an isolated incident or not. Hence the SB and AD.
this is the data gathering stage where they find out if it's a widespread issue or not.
Ive been reading others posts about the two stages of locking. This is a must on any flight control. Dont forget though that they are only safety nets to the initial locking, which is the correct torque on the nut. Continual inspections offer the final net of safety.
In essence what I am saying is there was 4 failures here.
The torque was lost/incorrect or was never applied, allowing the nut to un-thread.
either faulty cotterpin/lockwire, or missing cotterpin/lockwire the failure was just a matter of time.
and the 4th, the inspections, didn't catch the impending loss.
Personally I think the loss of the nut would have happened quickly once torque was lost and the safety features failed to retain it.
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Interesting. As stated in the EAD, perhaps simply a precautionary measure based on what was observed in the accident. It would appear there is though, a way in which the mechanism can be incorrectly installed/assembled that has been either observed or imagined and is causing concern. Of course this may yet not apply in the case of this recent accident.
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I wonder whether an incorrect assembly, rather than lose a nut, could cause a misalignment or deformation of the link/control rod, resulting in a jamming of the control rod.
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GRAYHORIZONSHELI Do you actually mean “they found a missing nut” or “they found that a nut is missing”?
I would assume (and surely at this stage of the game, it’s still an assumption) it would be the latter.
I stress again, I am not a pilot, but I am a mech engineer (albeit from a different discipline). As a slight aside, I have used split pins and wire locks on many a track motorcycle in my time, so as well as those two safety measures, there is (as you stated) the correct torque setting for the nut. On top of that, I don’t know if the aviation world use it or not, but on track bikes, it was also common practice to apply a further safeguard in the form of an appropriate thread locking fluid (yes, usually from the Loctite company).
I would assume (and surely at this stage of the game, it’s still an assumption) it would be the latter.
I stress again, I am not a pilot, but I am a mech engineer (albeit from a different discipline). As a slight aside, I have used split pins and wire locks on many a track motorcycle in my time, so as well as those two safety measures, there is (as you stated) the correct torque setting for the nut. On top of that, I don’t know if the aviation world use it or not, but on track bikes, it was also common practice to apply a further safeguard in the form of an appropriate thread locking fluid (yes, usually from the Loctite company).
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First time poster, long time lurker here!
Hopefully I can answer some of the questions posted about the TRA (Tail Rotor Actuator).
The input lever will drive a dual main control valve to control both hydraulic systems. The position feedback is via the trunnion block (90). I would imagine, and I don’t know this specific actuator, that the control valve will be spring biased to return the actuator to a neutral position if the pilot input is lost. If the position feedback is lost the actuator will run away to a hardover position.
If the washer (140) was incorrectly installed position control would still be present, but the null and full stroke positions of the actuator would be affected . This will be installed and checked (visually and by test) at the manufacturer, as would the nut (60) and cotter pin (50). These parts would never be removed from the actuator unless it was undergoing some repair work (removed from the airframe).
As far as a nut going missing, I think that the thread is handed such that the rotation of the Tail Rotor always tightens the rod into nut. If the nut is missing then I would guess that it was a mechanical failure somewhere.
Hopefully I can answer some of the questions posted about the TRA (Tail Rotor Actuator).
The input lever will drive a dual main control valve to control both hydraulic systems. The position feedback is via the trunnion block (90). I would imagine, and I don’t know this specific actuator, that the control valve will be spring biased to return the actuator to a neutral position if the pilot input is lost. If the position feedback is lost the actuator will run away to a hardover position.
If the washer (140) was incorrectly installed position control would still be present, but the null and full stroke positions of the actuator would be affected . This will be installed and checked (visually and by test) at the manufacturer, as would the nut (60) and cotter pin (50). These parts would never be removed from the actuator unless it was undergoing some repair work (removed from the airframe).
As far as a nut going missing, I think that the thread is handed such that the rotation of the Tail Rotor always tightens the rod into nut. If the nut is missing then I would guess that it was a mechanical failure somewhere.
#697 https://www.pprune.org/10304706-post697.html
full link of EASA E- AD https://ad.easa.europa.eu/ad/2018-0241-E
full link of EASA E- AD https://ad.easa.europa.eu/ad/2018-0241-E
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GRAYHORIZONSHELI Do you actually mean “they found a missing nut” or “they found that a nut is missing”?
I would assume (and surely at this stage of the game, it’s still an assumption) it would be the latter.
I stress again, I am not a pilot, but I am a mech engineer (albeit from a different discipline). As a slight aside, I have used split pins and wire locks on many a track motorcycle in my time, so as well as those two safety measures, there is (as you stated) the correct torque setting for the nut. On top of that, I don’t know if the aviation world use it or not, but on track bikes, it was also common practice to apply a further safeguard in the form of an appropriate thread locking fluid (yes, usually from the Loctite company).
I would assume (and surely at this stage of the game, it’s still an assumption) it would be the latter.
I stress again, I am not a pilot, but I am a mech engineer (albeit from a different discipline). As a slight aside, I have used split pins and wire locks on many a track motorcycle in my time, so as well as those two safety measures, there is (as you stated) the correct torque setting for the nut. On top of that, I don’t know if the aviation world use it or not, but on track bikes, it was also common practice to apply a further safeguard in the form of an appropriate thread locking fluid (yes, usually from the Loctite company).
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.
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Those familiar with this particular aircraft have already stated that this particular component requires the removal of a cover for inspection. That being the case, should any component part company from its design location, there is every likelihood that it would be retained by the cover and remain with the aircraft rather than be found on the stadium playing surface. Would that be (yet another) fair assumption?
Again, in terms of scale, I don’t know how big or small this component actually is.
Again, in terms of scale, I don’t know how big or small this component actually is.
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First time poster, long time lurker here!
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If the washer (140) was incorrectly installed position control would still be present, but the null and full stroke positions of the actuator would be affected . This will be installed and checked (visually and by test) at the manufacturer, as would the nut (60) and cotter pin (50). These parts would never be removed from the actuator unless it was undergoing some repair work (removed from the airframe).
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If the washer (140) was incorrectly installed position control would still be present, but the null and full stroke positions of the actuator would be affected . This will be installed and checked (visually and by test) at the manufacturer, as would the nut (60) and cotter pin (50). These parts would never be removed from the actuator unless it was undergoing some repair work (removed from the airframe).
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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.