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USN MH-60S Down San Diego

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USN MH-60S Down San Diego

Old 3rd Sep 2021, 20:39
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USN MH-60S Down San Diego

San Diego Tribune is reporting a Seahawk crashed on the flight deck of the carrier Abraham Lincoln off San Diego ,Wednesday ,5 missing 1 rescued from the ocean .Search continues .Thoughts and prayers are with all concerned .
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Old 8th Sep 2021, 13:40
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Thanks, my initial post seems to have drifted down a bit. I deleted it, as yours has a better title.
The Navy reported that an MH-60S Knighthawk operating from the Abraham Lincoln (CV-72) went into the ocean about 60 miles off shore. Six souls on board, one recovered so far. Early report from a local newspaper here.
Some follow up information that doesn't really answer many questions (Navy has confirmed that the other 5 personnel on board have lost their lives ).
I have gone through the Naval Safety Center web page and can't find the summary the news sources are referring to.
The helicopter reportedly touched down on the flight deck and "experienced side-to-side vibrations." It caused the main rotor to strike the deck and fall over the side of the aircraft carrier.
Another source described it a little differently
The MH-60S Knighthawk began undergoing ``side-to-side vibrations'' while landing on the aircraft carrier USS Abraham Lincoln during a routine flight operations roughly 60 nautical miles from shore about 4:30 p.m. last Tuesday, according to a brief preliminary accident summary released by the Naval Safety Center. As the aircraft lurched back and forth, its main rotor struck the deck of the ship, and the impact caused the helicopter to tumble into the sea, the agency reported.
My estimate is something like dynamic rollover (presuming a heading roughly in the direction ship was heading near spot 3 or 4 on the port side of the flight deck, which is where helicopters usually arrive and depart on a CVN)
but
since I have no idea what "experienced side to side vibrations" refers to it's not a very well informed estimate.
Note: I flew and instructed in Seahawks but it's been a while. Based on the information available, which is sparse, that's all I can come up with for why (a) the main rotor blades struck the deck and (b) it then went over the side.
There may be another explanation, though, which may render this estimate moot as more information becomes available.
The "lurched side to side" observation may point toward a hydraulic, or flight control, system anomaly of some kind.
FWIW, an old version of the NATOPS manual for the CH-60S identifies 15 degrees as a critical angle (regarding sloped landings/takeoffs) but points out that there's a lot more to it than that ...
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Last edited by Lonewolf_50; 8th Sep 2021 at 14:07.
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Old 8th Sep 2021, 16:42
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I would suggest the 'side to side' vibration was ground resonance rather than dynamic rollover.

I had this very badly in a Wessex many years ago on rotor start due to unequal tyre pressures (servicing error) and by the time I retarded the speed select lever and applied the rotor brake each wheel was alternately lifting over a foot off the ground and the ground crew were heading in the opposite direction very quickly.

Fortunately we didn't rollover but it was a scary moment.

It can be a function of tyre pressures, oleo pressures or a MR imbalance aggravating the natural frequency of the undercarriage.

The sequence of events described in the reports matches exactly an uncorrected ground resonance situation - eventually the rapidly increasing magnitude of the 'padding' would cause a rotor strike.

The solution is to lift to the hover if you have flying Nr.
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Old 8th Sep 2021, 20:49
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Originally Posted by [email protected] View Post
I would suggest the 'side to side' vibration was ground resonance rather than dynamic rollover.
The report did not indicate that the aircraft was chained / chocked to the deck, which is why I didn't think of that as an issue. But I suppose that there are a variety of ways to enter ground resonance.
Beyond that I won't go - if they landed, got into ground resonance, and didn't lift back off right away I can see the point you are making.

But I am guessing again here.

I don't remember how badly the lateral vibes get when the main rotor dampers leak all of their fluid out, but I do not recall that particular mechanical failure being taught to us as so severe that it makes the aircraft unflyable. Perhaps John Dixson may be able to shed some light on that if he drops by).

There's another possible scenario that occurred to me during lunch.

A few hears ago a UH-60L (from which the CH-60S => MH-60S is directly descended) had a considerable length the skin (aft of the spar) on a main rotor blade come off in flight. The aircraft got a heavy vibration, the crew did an autorotation, and they reported very heavy vibes at the bottom when they cushioned the landing at the end. (All walked away).
That offers me another possible scenario as I think through that very sparse report: what got that observed lateral behavior started?
If, as they approached the ship, a similar blade skin dis-bond happened, severe vibes would show up since they still had power on. Again, the lack of detail leaves this as "a guess" ... I suspect that it will be a while before more is known as the investigation has begun in earnest.

Thanks for sharing your thoughts, crab.
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Old 9th Sep 2021, 08:41
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Lonewolf - yes I think a blade delamination or a faulty drag damper could easily cause the resonance - we had a situation in NI many years ago where a blade drag damper lock was left in and the aircraft started up. It was stable enough until flying Nr was reached and then it went pear-shaped very quickly - ISTR the crew got it airborne and then carried out a prompt running landing, shutting down the rotors as soon as the wheels touched the ground. Wessex pilots were very au fait with ground resonance issues.

I can imagine a crew, unfamiliar with the rapid onset of ground resonance, wanting to keep it on the deck as you don't know if it will get worse in the air - good idea but shut down the rotors immediately.

We used to demonstrate a damper check as part of the airtest qualification on the Sea King - you sat in the hover and circled the cyclic once or twice (fairly small circles but quickly) and then stopped to see how long it took for any oscillations to stop - a faulty drag damper was evidenced by a slow to reduce 1R.

It was possible to set up a sympathetic oscillation in the rotor which persisted as a 5R for a few seconds and was very unpleasant - a pilot who was trying to fault diagnose a damper issue managed exactly this and though he had lost control, dumped the lever and trashed a perfectly serviceable aircraft.
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Old 9th Sep 2021, 12:17
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Crab and Lonewolf:

The ground resonance testing ( mechanical stability is the term used in the Engr Dept ) involves depleting the MR damper fluid, the tire pressure and the landing gear strut servicing. The Naval aircraft main gear ( Seahawk ) are quite different than the Army S-70 gear BTW*. In any case neither was conducive to the rapid entry into ground resonance experienced on the S-58.
*The Army gear design was greatly influenced by their very severe crash-worthy requirements, while the USN gear was very influenced by the frigate landing requirements. Those who have been to PXT can still see the 50 x 50 ft pad they built on a 9 degree slope. Landing at 12 ft/sec was “ interesting “. Actually we had asked for a larger pad, but the USN gave us 50. Trouble was that getting the vertical speed under control within 1 ft/sec isn’t easy and we were starting well above 100 ft and I couldn’t see the pad, even after taking the door off. Solution was that Seahwak Test Director CDR Jack Costello put on a flight suit, acquired a prtable UHF radio, stood on that slope and gave us a GCS for the first part of the descent. He was, as you can imagine, pretty close to the ship when we hit the ground.
Jack Costello, in a previous career, had flown Seals into North Vietnam in a UH-2.
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Old 9th Sep 2021, 15:57
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Originally Posted by JohnDixson View Post
Crab and Lonewolf:

The ground resonance testing ( mechanical stability is the term used in the Engr Dept ) involves depleting the MR damper fluid, the tire pressure and the landing gear strut servicing. The Naval aircraft main gear ( Seahawk ) are quite different than the Army S-70 gear BTW*. In any case neither was conducive to the rapid entry into ground resonance experienced on the S-58.
*The Army gear design was greatly influenced by their very severe crash-worthy requirements, while the USN gear was very influenced by the frigate landing requirements. Those who have been to PXT can still see the 50 x 50 ft pad they built on a 9 degree slope. Landing at 12 ft/sec was “ interesting “. Actually we had asked for a larger pad, but the USN gave us 50. Trouble was that getting the vertical speed under control within 1 ft/sec isn’t easy and we were starting well above 100 ft and I couldn’t see the pad, even after taking the door off. Solution was that Seahwak Test Director CDR Jack Costello put on a flight suit, acquired a prtable UHF radio, stood on that slope and gave us a GCS for the first part of the descent. He was, as you can imagine, pretty close to the ship when we hit the ground.
Jack Costello, in a previous career, had flown Seals into North Vietnam in a UH-2.
Wow, that's a blast from the past. Jack Costello. Had not heard his name in some years (I remember first meeting him when I was a JO flying SH-2F's).
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Old 9th Sep 2021, 16:30
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Jack also saved a member of the Sikorsky Engr crew. This person was in a saloon in the PXT area ( an SA crew was crewing/assisting the USN during some follow-up testing ) and got into a " loud discussion " with the guy next to him in the bar. It progressed and they went outside to settle the matter......except this guy's two pals also went outside, so our guy wound up getting beat up by three. Jack went outside to see how things were going, saw what was happening and ( oh, I forgot to mention that Jack boxed in college and had been a bouncer to earn some spending $ ) decked the three fellows. Should have put Jack in for a Winged S Award*
*get one of these if you rescue someone while flying a Sikorsky helicopter.....well...this was sorta in line with the basic idea..
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Old 10th Sep 2021, 04:44
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rapid entry into ground resonance experienced on the S-58
We had a H-34 at Ellyson that fell on its side during a mag check - at least that's what we were told was the cause.
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Old 11th Sep 2021, 09:53
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King Stallion to the rescue

The first real world mission for the Flying Leathernecks new King Stallion involved the recovery of said MH-60S. Pair of VMX-1 King STallions were undergoing OT & E at 29 Palms nearby so they got the call from the Navy Safety Center to assist with the lift.

https://www.navair.navy.mil/news/CH-...-09082021-2033


cheers




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Old 11th Sep 2021, 20:39
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Originally Posted by chopper2004 View Post
The first real world mission for the Flying Leathernecks new King Stallion involved the recovery of said MH-60S. Pair of VMX-1 King STallions were undergoing OT & E at 29 Palms nearby so they got the call from the Navy Safety Center to assist with the lift.

https://www.navair.navy.mil/news/CH-...-09082021-2033


cheers
https://www.thedrive.com/the-war-zon...-world-mission

Here's a good article covering the lift.
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Old 4th May 2022, 19:36
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Crash Report

Report:

https://www.cpf.navy.mil/Portals/52/...5ijQ384A%3d%3d

From the report:

The mishap was caused by the failure of the yellow damper hose on LT 616 in-flight, resulting in total loss of main rotor system damping and the immediate onset of severe vibrations upon touchdown.
So the accident was caused by ground resonance resulting from rotor head line failure. If the report is taken literally a single fluid hose to a single damper failed resulting in the loss of damping in all four blade dampers!! How can this be true? Can someone familiar with the design verify that this is not the case? If true how could such a design be approved?

Assuming that the report’s wording was poorly chosen and should have been “loss of damping to the single blade”, this raises the further question on why loosing a single blade’s damper would be catastrophic? Note: Commercial certification requires demonstrating safe operation with a single damper failed.

Last edited by The Sultan; 4th May 2022 at 20:07.
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Old 4th May 2022, 20:20
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Originally Posted by The Sultan View Post
If true how could such a design be approved?
If you look at the millions of flight hours that the S-70 has flown since introduction, because it works. (Seahawk and Blackhawk share that common lineage).
For What It's Worth: not surprised that the lateral disturbance seems to have been related to dampers. In my experience, main rotor dampers were a source of never ending attention, and frustration, when I was in the Fleet around 30 years ago. I would need to dig into the NAVSAFCEN's data base on mishaps to dig out such ones as had dampers as a contributing factor, but it's been a long time since I was in a job that allowed me access to that.
I suspect that there is a little more to be learned on this. I'd love to see if any changes to the NATOPS were made for the CH-60S as a result (in terms of 'if you run into this, do that') instructions.
No further speculation will be made by me.
PS: thanks for the link, the JAGMAN report will get a more thorough read from me later on.
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Old 5th May 2022, 06:10
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You have two options when you encounter ground resonance like that - either get airborne again or shut down really quickly, it would seem the pilot did neither.
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Old 5th May 2022, 06:25
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automatic blade folding


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Old 5th May 2022, 09:43
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Originally Posted by [email protected] View Post
You have two options when you encounter ground resonance like that - either get airborne again or shut down really quickly, it would seem the pilot did neither.
The surviving crewman states on Page 20 that he saw the pilots attempting to secure the PCLs. I guess the vibrations prevented them doing so in time.
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Old 5th May 2022, 10:11
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The surviving crewman states on Page 20 that he saw the pilots attempting to secure the PCLs. I guess the vibrations prevented them doing so in time.
Hence my comment about doing it really quickly - in ground resonance the amplitude and severity of the oscillations increase very rapidly so if you have dithered whilst trying to diagnose the problem, you are already on your side.

Only good awareness amongst the Wessex fleet about the problem and good training by the RAF prevented me from ending up, like them, as the owner of a big pile of scrap.
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Old 5th May 2022, 14:45
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Crab,

As Lonewolf stated this is not a common event and the report indicated there was no warning prior to the incident. You have to allow 1-2 seconds to realize their is a problem before anyone can be expected to respond. The pilot attempted to shut down the engines, but events over took them almost instantly. To get the result you put forward the crew would have had to know of the problem, prepared for it and done a hovering throttle chop with max collective and hope the rotor rpm dropped below the critical frequency before the oscillations became destructive. If the problem had been annunciated the best course may have been to ditch.
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Old 5th May 2022, 14:55
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Sultan - I disagree, I have encountered full on ground resonance in a Wessex and the early stages in Sea King - there is enough time to do something about it but you need to have been trained to recognise and deal with it.

As soon as they landed and experienced the 'padding' that precedes GR, they should have lifted to the hover - if the oscillations stop, that is when you consider a running landing or a low hover throttle chop.

How much GR awareness is there amongst the Blackhawk users? If it is a very unusual occurrence on that aircraft then it is understandable why they didn't recognise it and act quicker.
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Old 5th May 2022, 15:33
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I shall agree with Crab on this one....yes I know.....mark it on the calendar as it is somewhat rare.

In my past I flew the Hughes 269/TH-55, a very limited exposure to the H-19 (Whirlwind to our British friends), the H-34/S58T, and the Alouette III which all were candidates for the Fastest Self Destruction Competition.

Starting in primary flight school we were exposed to the dangers of Ground Resonance....those of us who were flying the TH-55 and not the H-13 or H-23 had to know about.

Recognizing the onset of Ground Resonance is the most important issue....knowing what it feels like (we had demonstrations of it in our training) and then immediately doing as Crab said....Pick up to a Hover or shut down the engine(s) and decrease the Rotor RPM as quickly as possible are the two options.

It is not the shut down of the engine that makes the real difference....it is the Rotor RPM and the Angular out of balance of the Rotor system.....changing the resonance and reducing the forces generating the resonance is key.

In the video....the second Hughes 269/300 clip shows how the quickly the resonance dissipates after lifting off the ground as the aircraft is free of the surface and the feedback from contact with the surface

The chinook clip shows the aircraft was tied securely to the ground and the aircraft landing gear struts were unable to function as designed......and despite the Test Engineers shutting the engines off.....there was no way to slow the blades quickly as the aircraft did not have a Rotor Brake.




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