Dynamic components after rotor strike

[Agile]

Can somebody educate me:
Assume a main rotor gearbox and epicycle (with 300h since New) is involved in a roll over, rotor head and blades are damaged biggly, but gear box looks quite OK.
what hapen to such component:
A: inspection and dynamic testing
B: complete regular 3000h overhaul
C: discarded

if somebody knows how it works please let me know

Thanks

[Jetstream67]

Hopefully destroyed before recycling the materials. I’d hate to be relying on it …

[GoodGrief]

You want to buy the parts from the TIMO accident ?

[Fortyodd2]

Answer - C.
Having seen the internals of a main rotor gearbox that "Looked quite okay" from the outside - the pinions inside it had twisted almost 2 and a half times before snapping.

[SASless]

I'd vote for junking all rotating components right the way back to the Tip of the Tail rotor....and start over after making sure the airframe isn't warped or transmission mounts harmed.

A long chat with the Aircraft Manufacturer and getting their input would be wise as well.

[Agile]

You want to buy the parts from the TIMO accident ?
Well I just put 2 and 2 together: the thread of the TIMO accident and the other thread about EC120 component cost wanting all new components.

that question has been naging my mind:
how much over torque a rotor strike actually is on the MGB?
isn't the inertial shock all from the blades own inertia?
with modern testing method can't we revalidate a part fully?

[ericferret]

Well I just put 2 and 2 together: the thread of the TIMO accident and the other thread about EC120 component cost wanting all new components.

that question has been naging my mind:
how much over torque a rotor strike actually is on the MGB?
isn't the inertial shock all from the blades own inertia?
with modern testing method can't we revalidate a part fully?

Firstly G-TIMO appears to have suffered a sudden stoppage not a blade strike, there is a difference.
Dont forget the engine is still driving as well unless it had been shut down or failed.

We had a 365 that had a tail strike which lead to the fenestron cutting a slot in the duct.
The main gearbox was found to have a hard spot in rotation and was replaced with the other tail drive components..
What was missed was that the engine manufacturer required the engines to be inspected.
Shortly after return to service the aircraft suffered an engine failure.
This incident would have been classed as a strike not a stoppage.

[Mee3]

Well I just put 2 and 2 together: the thread of the TIMO accident and the other thread about EC120 component cost wanting all new components.

that question has been naging my mind:
how much over torque a rotor strike actually is on the MGB?
isn't the inertial shock all from the blades own inertia?
with modern testing method can't we revalidate a part fully?
Its not your choice. AH requires scrapping all dynamic in TIMO case. Overhaul can only save those scenario describe in AMM but will cost you half of new.

[Ascend Charlie]

Look at any video where a main rotor hits a cable, or clashes with another rotor, the whole tail boom is shaken off. Huge forces at work, I wouldn't trust any of those components.

[wrench1]

Can somebody educate me:
Assume a main rotor gearbox and epicycle (with 300h since New) is involved in a roll over, rotor head and blades are damaged biggly, but gear box looks quite OK.
what hapen to such component:
A: inspection and dynamic testing
B: complete regular 3000h overhaul
C: discarded

if somebody knows how it works please let me know

Thanks
Most OEMs have either a published rotor strike special inspection or provide a tailored inspection specific to the incident. Depending on the inspection some are tiered by the level of blade damage or if the blade was powered or not. In your examp!e, I believe those components would require at least an overhaul based on my experience with a proper note on the incident. In addition there will probably be engine related inspections as well due to the strike. The manuals would give more details.

[DuncanDoenitz]

It's an open and shut case; the entire power-train, transmission and rotors are unserviceable until a Certificate of Release to Service is issued by an approved maintenance organisation. That is only going to happen if:

1. The type of occurrence is one that's listed in the Special Inspections in the MM, and inspected/repaired accordingly.
or,
2. The circumstances are referred to the Type Certificate Holder, and specific-to-incident approved data is used to inspect/repair.

[ericferret]

It's an open and shut case; the entire power-train, transmission and rotors are unserviceable until a Certificate of Release to Service is issued by an approved maintenance organisation. That is only going to happen if:

1. The type of occurrence is one that's listed in the Special Inspections in the MM, and inspected/repaired accordingly.
or,
2. The circumstances are referred to the Type Certificate Holder, and specific-to-incident approved data is used to inspect/repair.

The wreck becomes the property of the insurance company who sell it for the best price they can get.
This is the point that the dark arts kick in.

[wrench1]

This is the point that the dark arts kick in.
Well the black art side is finally getting harder depending on your view point. Airbus has seen the light so to speak and now provides a listing of scrapped or destroyed aircraft like other OEMs do. They also provide a means to check serial numbers of items if needed. Have had several checks done but thankfully all was on the up and up with some spare components on the market.

[rotorrookie]

Look at any video where a main rotor hits a cable, or clashes with another rotor, the whole tail boom is shaken off. Huge forces at work, I wouldn't trust any of those components.
remember this one few years ago nz 350 crash during sling ops at same second the main rotorblade hits the cable the tailboom snaps off

[ericferret]

Well the black art side is finally getting harder depending on your view point. Airbus has seen the light so to speak and now provides a listing of scrapped or destroyed aircraft like other OEMs do. They also provide a means to check serial numbers of items if needed. Have had several checks done but thankfully all was on the up and up with some spare components on the market.

True but many aircraft out there have no linkage to the manufacturer.
They can't provide listings that they do not possess.

[wrench1]

True but many aircraft out there have no linkage to the manufacturer. They can't provide listings that they do not possess.
No "linkage" required. The list is update from 3rd party sources. Last I looked the Airbus destroyed/salvage listing had over 5000 aircraft by model and S/N. While its not perfect it does give a benchmark to research from. For example, the Kiwi Xmas tree B2 above is on the list.

[Mee3]

No "linkage" required. The list is update from 3rd party sources. Last I looked the Airbus destroyed/salvage listing had over 5000 aircraft by model and S/N. While its not perfect it does give a benchmark to research from. For example, the Kiwi Xmas tree B2 above is on the list.
actually if you contact local ah rep, they can pull up latest status of any sn within minutes. Even its not official, they can tip you what they know.

[Agile]

I do not think it is the role of the OEM to police which airframe should be flying and which airframe should not. (especially when it is in their best intrest to "black list" as many serial number as possible to have the least airframe loose on the market)
why do we have an airworrthiness certificate system then? are we saying it cannot be trusted. if something can be repaired, or inspected according to established procedures, it should get an authorized release form, and if it does it should be authorized by the authority FAA - EASA - CASA - CAA ....

[wrench1]

I do not think it is the role of the OEM to police which airframe should be flying and which airframe should not. (especially when it is in their best intrest to "black list" as many serial number as possible to have the least airframe loose on the market)

The list is merely advisory by the OEM. They have no legal power to "blacklist" any aircraft. Does the OEM have liability, sure, and that was the reason Bell originally started listing aircraft thought to be destroyed or scrap as they were sued over an aircraft that was not original under its data plate.

why do we have an airworrthiness certificate system then? are we saying it cannot be trusted.

It's not the systems fault as it was not designed to cull out illegal aircraft. Since an AWC is usually issued only once to an aircraft, if one were to remove the AWC, registration, data plate, and logbooks from the original aircraft and use those documents/records with any other aircraft nobody would be the wiser. And given there are people who prefer money over conformity you as a buyer may end up with an aircraft or component with a fraudulent history. There was a previous thread on Pprune about this same issue.

if something can be repaired, or inspected according to established procedures, it should get an authorized release form, and if it does it should be authorized by the authority FAA - EASA - CASA - CAA ....

And it still can. I don't know about the other agencies but the FAA has guidance on determining destroyed/scrapped aircraft and the method(s) for which to rebuild that aircraft if one so chooses. Its not the people who want to follow thew rules that caused this, but those individuals who think its okay to break those rules for personal gain.

[airsail]

I ran a Bell component overhaul shop for a short time. We were often sent components for recertification from third party parts suppliers. We had to be extremely careful with drivetrain components as the Bell sudden stoppage inspection states that if you find any damage as you do the inspection, many components require scrapping, not overhaul.

We had a case where a one 212 fly bar arrived for recertification, the book stated that any damage, both were scrap. I thought it unusual that we asked to only recertify one, not two, this involve a full visual and MPI inspection. We asked were the other bar was, no comment, just send that bar back uncertified.

No idea how many of these types of parts are floating around awaiting recertification.

[industry insider]

Didn't the fatal accident 225 MGB which failed in Norway in 2016 have an episode where it fell off a truck on its way from Perth to Broome in Western Australia?

[albatross]

Didn't the fatal accident 225 MGB which failed in Norway in 2016 have an episode where it fell off a truck on its way from Perth to Broome in Western Australia?
Yes I heard that too. However I also heard that the transmission was sent to Airbus for overhaul.

[roscoe1]

The question that I don't think is answered outside of Airbus is how deep they went in to " repair" the Puma gearbox after it fell of the truck. The mfg. said it was repaired properly and that makes it legal. It might have been good as new or it might have been the initiation for the failure because something was missed on a bearing race. The assumption has to be that they knew exactly what happened and did what needed to be done and that the failure was unrelated because nothing could ever be proved linked to sliding off a truck bed.

As long as there is a population of people certified to perform overhaul and repair by manufacturere and airworthiness authorities, there will be people willing to take chances on components as pointed out above, without being sure of the history. There will always be complicit people who send components out to these shops without adequate description of what the real status of the part is. The question is, is it wrong to perform an overhaul, per the manufacturers specs, on a component that appears de-novo on your doorstep with a request for overhaul, without being able to be absolutely sure about the circumstances that brought it to you? Having been a chief inspector at an MRO and seen parts from a known wreck appear for overhaul, my answer is absolutely not. Safety issues notwithstanding, for no other reason because you cannot know how the legal system will treat you if there is an issue down the road. I'm retired now and feel very fortunate to never have been associated with an aaccident that caused an injury or worse. The manufacture and the airworthiness authorities always tell you the MINIMUM that you MUST do. Hardly ever do they write down what you SHOULD do to look after everyone's best interests. That list is left to the conscience of the MRO. It costs a lot of money to fly around. Too bad, it's just the cost of doing business.

[Bksmithca]

The question that I don't think is answered outside of Airbus is how deep they went in to " repair" the Puma gearbox after it fell of the truck. The mfg. said it was repaired properly and that makes it legal. It might have been good as new or it might have been the initiation for the failure because something was missed on a bearing race. The assumption has to be that they knew exactly what happened and did what needed to be done and that the failure was unrelated because nothing could ever be proved linked to sliding off a truck bed.

As long as there is a population of people certified to perform overhaul and repair by manufacturere and airworthiness authorities, there will be people willing to take chances on components as pointed out above, without being sure of the history. There will always be complicit people who send components out to these shops without adequate description of what the real status of the part is. The question is, is it wrong to perform an overhaul, per the manufacturers specs, on a component that appears de-novo on your doorstep with a request for overhaul, without being able to be absolutely sure about the circumstances that brought it to you? Having been a chief inspector at an MRO and seen parts from a known wreck appear for overhaul, my answer is absolutely not. Safety issues notwithstanding, for no other reason because you cannot know how the legal system will treat you if there is an issue down the road. I'm retired now and feel very fortunate to never have been associated with an aaccident that caused an injury or worse. The manufacture and the airworthiness authorities always tell you the MINIMUM that you MUST do. Hardly ever do they write down what you SHOULD do to look after everyone's best interests. That list is left to the conscience of the MRO. It costs a lot of money to fly around. Too bad, it's just the cost of doing business.
I think that your trying to make an orange an apple. A gearbox or engine that falls off a truck is going to likely sustain some damage. But an engine or gearbox that stops suddenly because of accident is going to sustain a lot of damage some of it visible and some of it won't be know until someone attempts to use it on an airframe. I think that the regulators as a whole need to ban the reusing of any part involved in an accident

[wrench1]

airsail: No idea how many of these types of parts are floating around awaiting recertification.
While there still are those types of parts floating around in the system, their numbers have been decreasing in my experience thanks to technology. Once where the only records were local hardcopies are now part of a digital system that can be accessed on a global scale. Unfortunately, there still are operators who look for the cheapest path to follow which keeps that part of the system viable.

[roscoe1]

I think that your trying to make an orange an apple. A gearbox or engine that falls off a truck is going to likely sustain some damage. But an engine or gearbox that stops suddenly because of accident is going to sustain a lot of damage some of it visible and some of it won't be know until someone attempts to use it on an airframe. I think that the regulators as a whole need to ban the reusing of any part involved in an accident
Of course it goes without needing to say if the mfg says parts are to be pitched then out they go. In cases where that is not specified there will always be people who see no reason they shouldn't reintrroduce items that pass the prescribed inspection or overhaul back into service. You have no idea how far the gearbox fell, how it landed, if it was properly protected in a can or sitting on rubber tires. I think its fine if regulators were to ban reuse of accident parts or assemblies but they would never do that because there are too many parameters to define. Manufacturers would love it, operators would have some legitimate complaints. Turnng a t/r driveshaft into a twisted broken mess from a tail rotor strike might not be a reason to pitch a gas coupled compressor rotor or at least it's housing, for example. I am not saying it would be a good idea, just that it is more complicated in a world where people weigh money and convenience against what they think is being safe.

[industry insider]

Yes I heard that too. However I also heard that the transmission was sent to Airbus for overhaul.

Yes, albatross, that's correct. My opinion is that any such components should be scrapped to avoid any doubt.

[RVDT]

However I also heard that the transmission was sent to Airbus for overhaul.

And who told Airbus it fell off the back of a truck? I am sure the trucking company didn't adjust the paperwork.

Those in the field who change bits on them will tell you any dynamic components and in particular transmission components are shipped like eggs or better with tell tales and all sorts protection these days on all models.

[Agile]

Of course it goes without needing to say if the mfg says parts are to be pitched then out they go. In cases where that is not specified there will always be people who see no reason they shouldn't reintrroduce items that pass the prescribed inspection or overhaul back into service. You have no idea how far the gearbox fell, how it landed, if it was properly protected in a can or sitting on rubber tires. I think its fine if regulators were to ban reuse of accident parts or assemblies but they would never do that because there are too many parameters to define. Manufacturers would love it, operators would have some legitimate complaints. Turnng a t/r driveshaft into a twisted broken mess from a tail rotor strike might not be a reason to pitch a gas coupled compressor rotor or at least it's housing, for example. I am not saying it would be a good idea, just that it is more complicated in a world where people weigh money and convenience against what they think is being safe.Yes, the number of parameters to define is what makes the potential recovery method in-adapted and there goes the risk. Especially, rotor strikes can take so many different dimensions. From the heli tipping over with engine off (yes it happened when a drunk driver drove into an EMS heli) all the way to a full-blown shakeout as the movie shown above.

Take the rotor mast for example, it is stainless steel, if it proves to be dimensionally perfect upon inspection with high grade equipement. what are we to think?

a pure scientist would say: it proves the metal suffered no plastic deformations and thus as no memory of the event, it is then serviceable.
a person with a stake in the safety of the aircraft would say: I don't know…., scrap it!

The aviation industry has been long educated to change parts just because we don’t know any better, but in a world that will become increasingly resource constrained it hold little merit.

[RVDT]

Take the rotor mast for example, it is stainless steel

Really? Quote a model with a stainless steel mast.

[Agile]

Really? Quote a model with a stainless steel mast.
you are not talking to the expert here, but, I have references that show both the rotor mast of the AS350 astar and the top of the engine deck are stainless steel (I assume it is forged and stress relieved.. but I am drifting)

edit: a bit more research showsFerrium S53 (AMS 5922, MMPDS) is an ICME-designed, corrosion resistant, ultra-high strength steel for structural aerospace and other applications where 300M (BS S155) and 4340 are typically used, but S53 steel provides: much greater resistance to general corrosion and to stress corrosion cracking (SCC); excellent resistance to fatigue and to corrosion fatigue; and high hardenability. Its resistance to general corrosion is similar to that of 440C stainless steel, but it has much greater fracture toughness. S53 steel is double vacuum melted (i.e., vacuum induction melted and then vacuum arc remelted or "VIM/VAR") for high purity, leading to much greater fatigue strength. Because of its high resistance to corrosion and ultra high strength and toughness combination, S53 steel is being used in demanding landing gear and helicopter rotor shaft applications without the use of toxic cadmium coatings.

[Planetary]

Airbus provides guidance in SIN 3157-S-63.