Helicopter crash Hudson River 1

[LittleInch]

Helicopter sight seeing inner York crashed with all dead.

This video looks like it was flying at some speed, then something happens, it seems to change orientation very rapidly which causes the whole tail structure to detach, followed shortly by the main rotor blade and part of the gearbox. Horrible way to go.

https://www.reddit.com/r/CatastrophicFailure/comments/1jwfxh9/full_video_of_the_helicopter_crash_in_hudson

Six people killed after helicopter crashes into Hudson River in New York

Pilot and a family with three children who are believed to have been Spanish tourists were killed onboard aircraft

www.theguardian.com

 

[LittleInch]

Behind a pay wall unfortunately, but I get the gist. It did sound like a bit of a mom and pop operation.

The quote I heard when he said the pilot only had a few minutes of fuel left was rather alarming. He also seemed to be flying pretty fast for a tourist flight.

 

[TugboatEng]

There is a picture of the rotor still attached to the transmission with the mounting hardware on it still. It looks like it tore off a chunk of the airframe.

There is also a picture of the engine. In this design, the exhaust outlet is on the center and the combustor/turbine and compressor are on opposite ends. The compressor section is broken completely off. That is a possible source for the energy to break the airframe.

 

[Sym P. le]

From a New Zealand report here, a typical powerplant layout.

Also, from the first photo, it appears that the mast is significantly bent.

I noticed from the crash video that the entire drive bay was empty, leaving mostly just the passenger compartment. Posted are four cropped frames (not all successive (two pairs)) from one of the crash videos just before impact.

 

[waross]

Years ago I was hanging out in a hotel in the Yukon territory. That's east of a cold part of Alaska, but colder.
An exploration helicopter crew was stationed at the hotel.
One day I was sitting in the coffee shop when a helicopter landed.
The pilot was watching the rotors slow down.
That was strange.
That pilot generally jumped out as the bird hit the ground and headed for the coffee shop.
He often left his mechanic to shut off the engine.
I wandered out to see what was happening.
When the rotors were almost stopped, the pilot jumped up and grabbed a blade.
It had a shallow crease about 1 1/2 inches long.
The radio antenna was shattered at the end and the metal tip was missing.
The pilot remarked;
"I was flying at about 120 MPH and went into a steep dive.
The wind speed bent the antenna upwards and the rotors dipped downwards.
The blade hit the end of the antenna."
The blade had to be replaced.
I heard a price mentioned of about $7,000.
One of the pilots working there had lost a helicopter.
He touched down too hard and the rotor dipped down and cut off the tail.
The inertia of what was left of the rotors flipped the helicopter over and it burned.
Fortunately the pilot was thrown clear.
The only part salvaged was a spot light that was mounted on the front of one of the skids.

Back to the tragedy at hand.
My first thought is that something startled the pilot (a bird perhaps) and he made an abrupt pull on the cyclic stick.
The rotors tilted and contacted the mast.
Other than that we have to wait and see.

 

[TugboatEng]

The damage is largely concentrated in the compressor housing. It looks like the centrifugal compressor disk burst. Can these over speed if the load is abruptly removed? Maybe a gearbox failure led to a catastrophic overspeed.

 

[mfgenggear]

The damage is largely concentrated in the compressor housing. It looks like the centrifugal compressor disk burst. Can these over speed if the load is abruptly removed? Maybe a gearbox failure led to a catastrophic overspeed.

So I worked with gear boxes similar to this design , while I am not an engine expert I have dealt with loose gears for gear boxes.
From this OG memory this prat and Whitney PT 6 engine. Or similar. 10K RPM.
multi staged gear box gears to reduce rpm 1500-2000 rpm. Typically if the gears fail.
Catastrophic failure the gears from the engine self destruct. Parts break with high HP and RPM. Notice how the web and wall
Thickness is noticeably thin.
Safety factor is not much. It's to reduce weight . But I don't like jumping to conclusions. Wait for NTSB findings.

 

[thebard3]

Found this picture this morning. I know nothing about helicopters, but I did hear a lot about 'mast bumping' when it first happened. Does this picture suggest that both rotors are broken at about the same length by contacting the tail boom?

 

[Sym P. le]

How the turbine held on, by a few threads via the combustion chamber. We can see this in a similar orientation in the crash video (frame grabs posted above).

 

[Sym P. le]

Does this picture suggest that both rotors are broken at about the same length by contacting the tail boom?

I don't think so. The videos clearly show the assembly twirling down intact. I believe the blades broke on impact though I could be corrected.

It continually amazes me the penchant for popular knowledge regardless of its senselessness. We already have a clear photo of the self-destructed compressor stage.

Captain Steeve has a frank discussion on this incident and helicopter/pilot frailties. Though he also covers more popular knowledge, he doesn't come to any conclusions and hasn't reviewed the latest images.

 

[waross]

If the assembly was subject to the impact load of the rotor hitting the boom, the inertia may have done the damage to the turbine.

 

[Sym P. le]

Rinse and repeat.

 

[LittleInch]

Found this picture this morning. I know nothing about helicopters, but I did hear a lot about 'mast bumping' when it first happened. Does this picture suggest that both rotors are broken at about the same length by contacting the tail boom?
View attachment 8248

Mast bumping is something I had never heard of before, but seems to be when the helicopter goes low G on the top of a climb or sudden dive and its where the rotor blades flex out of plane and "bump" into the mast or the main rotor shaft which then basically breaks off. This doesn't look like this as the whole rotor assembly and what looks like a fair bit of the gearbox has been wrenched off as one unit. tug posted a video earlier on and if you make it through the first 5 minutes has a good explanation of it.

 

[Sym P. le]

 

[LittleInch]

The B roll from the NTSB is here https://www.ntsb.gov/investigations/Pages/ERA25MA171.aspx

First bit looks the most interesting but also that the chair of the NTSB is there as well. I'm very impressed with her whenever I hear her speak to the press.

The tail looks like it sheared off a the second set of rivets pretty cleanly. From the floor set it looks like they haven't recovered the tail section yet. Seems they have found it now, but not on the video.
No FDR or any internal video or data apparently.

 

[Alistair_Heaton]

On the turboprop engines they had a spline shear tube to disconnect the gearbox from the turbine section.

It did occasionally fail for no reason.

Don't have a clue how rotary do it.

That just sounds a nasty company. I have had numerous arguments over the years about sightseeing setups. Most of the time the pilots listening in to the family dispute have the decency to look embarrassed and not say anything. One even departed the job by the time we got back to leave the site. Maybe my comments about lifting 100kg blokes with only 100 ltrs of fuel in an R22 to stay in performance limits were a bit to close to the mark. It was windy and cold which is why it worked.

 

[LittleInch]

Going to be difficult to know what happened first, but looking at the tail damage and then at the right hand blade on post 27, that has all the look of a tail strike with the tip of the blade missing compared to the other blad, kind of matching the damage.

Now that might / may not be the root cause which is when the helicopter first does something very strange which causes it to yaw violently and then its starting to look like that bent the rotor blade down far enough to decapitate the tail. Once that happened that's the end of any sort of controllability.

 

[TugboatEng]

I do want to correct my comment about the compressor. The centrifugal stage appears to be intact. The axial stages are substantially damaged.

I have seen some references to Falk Grid type couplings being used on helicopters. They aren't exactly meant to shear under high loads but do shear cleanly when they do fail. Grid couplings are very sensitive to lubrication related wear. They require special shear stable lubricants due to centrifugal force an no stirring action.

 

[Sym P. le]

From the B-roll, ??

 

[mfgenggear]

What is interesting is how the tail rotor failed.
It appears to be a clean torsional failure.
Heare are some pics of the drive shaft components.

 

[waross]

Anecdote alert:
A story told by a retired tugboat captain;
His tugboat had just been fitted with new reversing gear.
They were doing sea trials with a company engineer from the gear manufacture on=board.
Steaming full speed ahead, the company rep requested the gear be shifted to full astern.
The company rep stated that the gear was designed to take that and he wanted to prove it in sea trials.
After some discussion, the captain made an entry in the log to the effect:
"Steaming full ahead. Going full astern at the direction of the company representative."
The gear was indeed capable of going from full ahead to full astern without damage to the gear.
Unfortunately the mounting was not so robust.
The gear broke its mounts and rotated, doing serious and expensive damage to the tugboat.
[/A]

The point?
Was a boom strike a result of a turbine failure or did the boom strike cause the turbine to break loose from its mounts.
Waiting to see the results of the investigation.
Possibilities:
Turbine failure; I expect that this will show wear and seizing of internal parts of the turbine.
Boom strike: I expect the turbine inspection to show little or no wear and no seizing. I expect the damage to be torsional breakage.
Both options open pending release of investigation results.