Another rotor break off in flight
 

Seems that this was in Korea. What type helicopter is that?

KAI Surion

https://en.m.wikipedia.org/wiki/KAI_KUH-1_Surion

Looks like a...

KAI KUH-1 Surion

"As the prime sub-contractor, Eurocopter has provided technical assistance in part for developing the power transmission, main gearbox, boom and tail gearboxes, automatic flight control system and rotor mast."
Just saying...

Regards.
Aser

Related development......332. Per that amazingly always accurate source....Wikipedia.

Sound familiar?

MUH-1 Marineon, a Surion variant.

Thats the mast snapping/separating at the head, rather than a gearbox internal failure ?

If you try to slow the video, or advance slowly, it seems as the coning angle is all over the place on takeoff. First it may appear normal, but seems to vary, then right around 9 seconds, when just over the last building, you can see the rotor tilt left, to the camera, then back forward. Then the cone angle drops, and raises again, before the rotor drops a lot around 10 seconds, one frame seems like blades are crowded in the front, spreads out flat again and one blade departs. The two other puma departures had intact heads and blades. I would not rule out a gearbox seizure as some have speculated, but probably not my first guess. But since this event was takeoff rather than cruise, all control positions and airflow vastly different, so the subsequent chain events could be different. Still, usually rotor heads and the blade roots tend to stay grouped, even after powered impact. This blade is missing at the head altogether, so I would suspect a blade attachment, or at least a blade control mechanism that could send this to extreme pitch, that would produce an extremely high load in the flatwise direction rather than chordwise, before separation. Who has graphics of rotor/ control system? Assume they are same as the AS332.

Except for the blade departure, clear in a 0.25x reproduction, I really need to check my glasses or get a bigger screen.

Looks like leading edge pitch control horns. If the mast or transmission let go, the blade roots would rise up while the pitch links remain at the same point.
This would produce a brief period of low or even negative pitch. Kind of matches the footage at the 10 sec mark when the coning angle of the rotor disk goes negative.
I think the missing red blade flapped down enough to contact the fuselage and sheared off at the hub.

MGB - same as 225
 

The Surion fleet has only recently returned to flight following a prolonged grounding due to the Norwegian 225 accident. They share a common MGB. This is terrible news.
RIP to those departed.

There was a big change in tail rotor rpm also. I'm going cross-eyed trying to tell if it was immediately before or simultaneous with the main rotor breakup/ separation.
Looks like first a rotor blade took out the windscreen with a simultaneous drop in TR rpm, then rapidly followed by main rotor separation.

The cone angle definitely goes very suddenly negative just before the break up, for me thats the cause. So perhaps a collective control link problem?

I have NEVER seen a MR Mast shear off like that!!! I also see a very abrupt change in RPM at 17 sec.

While you Video Geeks are examining the video....consider the actions of the entire rotor system immediately prior to the apparent separation of the one blade from the Rotor Head if you will.

I am wondering how the Rotor System would react to a sudden stoppage of the MGB particularly in the way each Blade would react both individually and as an attached part of the whole Rotor Head.

If the MGB seized and the Mast sheared off.....that would also shear the Pitch Change Links I am thinking.

As that happens very quickly....the effect on the Rotor Blade movements would also be very rapid and should (I am guessing) transmit a somewhat common reaction to all of the Blades.

Meaning to me....the Rotor Head would act more or less in a common manner and not shed individual blades.

If that Rotor Head moved such that a single blade made contact with a strong object (say the fuselage) then I can see a single blade being lost from the Head.

Do you see the whole Rotor Head Tip Path Plane tilting in such a manner or are we seeing a single blade launching off for points unknown while the rest of the blades act in a common manner?

It's really odd. It's like the fuselage ascended through the rotor disc. A rotor blade strikes the roof of the forward fuselage, buckles mid span then hits the windscreen and separates. Then the rest follows.:sad:

You have to use caution in determining rpm from video, aliasing can produce strange (even static) perceived rpm, as we see often on videos of rotors or props. It may be valid to say theres an rpm change, but whether it's positive or negative or how much is not really possible.

For me the accident sequence is:
- Sudden collective pitch change.
- 1 blade strikes fuselage & departs
- Out of balance rotor over-stresses the shaft and fractures

By private message....a suggestion was made a Swashplate Bearing failure could also be a possible cause for such a tragedy.

Meaning there is a reason they are called "Test Flights"?

The spindle fracture tells a big story.
This was not a repeat of the planetary failure chain of events, as I mentioned earlier, blades stay attached even after powered impact. Look at the tail rotor broom sticks, still attached. The separation is in a completely different spot, not at the conical housing, with struts and all.. No, I would strongly suspect that this started with the blade attachment shown broken in the photo.
fracture surface, even at the view shown, is not a clean shear, it has some jagged features on the aft side, and the area near it is clean from paint.
Then, there is an inward crushed area below and forward. This could be the indication of blade twist overload of the remaining segment of metal.
In this theory, crack exists, and is not detected, rigidity holds the geometry. Initial collective load is a "push" on push rod, blade twists, and crack opens further, BTM (Blade Twisting Moment). Damper loads contribute, possible to be complicit in root cause.
Airspeed increases, transitional lift allows collective to drop. Push rod "pull" begins local crushing, blade now unstable and flutters, before separating from rotor.
main shaft fractures from massive overload.

That was a difficult video to watch. I've never seen that before. I don't wish to see it again. Small mercy it was all over quickly for those aircrew on board. Only thing worse I can think of is the same thing happening from great height.

If we didn't have enough whatching a 225 rotor autorotating alone.....now this. What's the chance to caption that on video?
Anyway, whatever are the causes, I find hard for Airbus to recover from these images. It's more emotional than rational now.
RIP

These kinds of videos are akin to watching a Mid-Air Collision occur.....have seen two of those!

Once seen.....they cannot be un-seen....ever.

One per rev, . I am intrigued by the loss of paint. It is unusual to completely remove paint like this. I am not familiar with this structure, but is there a chance it was bonded at that location?

Blakmax

Maybe, the primer simply didn't stick to the metal and the top coat of paint ripped it off the way it did when the spindle fractured.
Given it was a post maintenance test flight, why would they have needed 6 people on board?

Regardless of the reason for the mainrotor to detach, it's a known fact that Airbus is heavily involved in designing and delivering main components to this aircraft programme.
How many airbus designed rotor disk detachments can be accepted within a relatively short timeframe? Regardless of the root cause, I belive airbus has a MAJOR problem.
The design of this main rotor mast looks very like the 225 mast, but with only four blades. It seems only to have small differences with the drag dampers, de-ice arrangement and dome fairing.
Pitch links, MRH sleeve and blade horns seems identical to the EC225.

This is my take on this accident:

What can cause a pitch link failure? Pitch link damage? Swashplate seizure/failure? Scissor failure?

edit: I also noticed that the pitch link connected to the blade horn of the ruptured sleeve has sheared off at the top, while the other two visible pitch links has sheared off/got the eyebolt pulled out of the pitch link tube at the bottom.

Again Airbus will put the blame on the maintenance crew involved in maintaining the aircraft as usual or they're gonna rule this out as a military prototype crash not in any way related to any other aircraft on the market today. Case closed! :mad:

Rest in peace fellow aviators. :(

Is this the straight 332L2 transmission and rotor system?

It's similar technology. The gearbox integration and rotor system are KAI's design, according to an AH subsidiary.

Correction: the rotor hub is KAI's design.

Spindle wall thickness looks a bit thin.

Surface finish looks a bit bright for paint adhesion.

That's a cheap slap on EC.

Pablo 332. This is my concern as well. I fail to see how paint can fail in this manner. I am a specialist in adhesive bond failure forensics and such a failure in an adhesive bond should ring alarm bells even if it is not a direct cause of the failure. I ask again if any part of that structure is adhesively bonded? If it was bonded then adhesion failures such as that are an extreme warning of exceptionally poor bond strength. If not, then questions must be asked about how paint can just peel off like that. Such a surface finish provides absolutely no environmental protection whatsoever. Adhesion failures in adhesive bonds or paint are indicative of exceptionally poor preparation processes. And before anyone suggests it, a crash event can never change the failure mode in adhesive bonds or paints. The interface is already exceptionally weak and impact can not cause such a change in failure mode.

Regards

Blakmax

Not to be discussed any further here, but my trust in airbus has worn very thin after the 225 accident in Norway.
Can agree that the last assertion is a bit cheap, but the first is a fact from the 225 accident.

Not many similarities with the L2 on this one, more similar to the 225 but with only four blades.
Sleeves, pitchlink, blade horn, droop restrainer support seems by looking at the pictures very similar to the 225.
The sleeves are actually shorter on the this aircraft compared to the 225, if you compare to the photo of the rotor head of the norwegian crash you will see it.
At last it's no doubt where they adopted the design from.

Paint peeling off is not uncommon in this area, at least not on the 225 which by the pictures seems to have used the same paint type, AH replaced this with a glossy light gray color after a while. Maybe they replaced the paint type only for civilian aircraft, I don't know.