AH-64 Tail Rotor Loss Article

[T28B]

I recommend the article in Air Clues 19 (see the sticky on this forum) (http://www.pprune.org/military-aviation/579095-air-clues-spring-summer-2016-issue-19-a.html)written by Lt Col Nick English, AAC, regarding a loss of tail rotor drive during a combat sortie in Afghanistan. Of particular interest to pilots (of all sorts) is his description of their decision processes, simulator training and it influence on this incident, and in general how the crew reacted to an emergency that began as the pilot flying sensing a vibration in the aircraft and then went downhill from there. If we had a thread on this in Rotor Heads or Mil Aviation, my search terms are not finding it.

[Thud_and_Blunder]

Strongly agree. The article came out just before I ran a simulator session highlighting that very topic for one of our line pilots; I think it's one of the most useful things I've ever read in Air Clues. Excellent skills, excellent article - excellent value.

[PDR1]

What came as a surprise to me was the statement that a current UK Military helicopter has an RTS which accepts that autorotations aren't usually successful (or whatever the pphrase was).

I'm no Heli pilot, but is that common with the current generation of military helicopters?

PDR

[Tourist]

What came as a surprise to me was the statement that a current UK Military helicopter has an RTS which accepts that autorotations aren't usually successful (or whatever the pphrase was).

I'm no Heli pilot, but is that common with the current generation of military helicopters?

PDR

There is a difference between "successful" meaning the sim considers that the aircraft survived the landing without gaining any more damage, and "successful" meaning that the crew survive.

In a multi engine helicopter, an auto is very rare.

[PDR1]

Yes, I appreciate that in a multi the need for an auto is more likely to be due to a tail rotor drive/control failure*, but I'm surprised that it's possible to certify a heli with that sort of characteristic.

That sounds like I'm disbelieving - I'm not! I'm just surprised. Did someone show that the probability of needing a full autorotation was below the 1 in 10^9 threshold with an ALARP argument?

PDR

* although weren't the Sea Kings prone to transmission failures if they had an engine failure when hovering out of ground effect when doing things like mountain rescue? Something in my memory talks about it being very marginal and prone to over-torquing failures on the remaining engine, but I may have made it up

[Arm out the window]

Quick question if anyone knows the answer - as I read it, the pilot in the article discusses how he didn't do an auto as per the standard training, but used a technique he'd developed by practicing in the sim until he could achieve a safe landing some of the time.

There's mention of not wanting to land at high speed (great idea); he also talks about getting the engines off (or to idle?) and achieving an autorotational state, taking control of the aircraft and landing safely as per this personal technique.

I assume what he's talking about is getting most of the forward speed off in a flare, then cushioning on as you normally would in a smaller helicopter, or at least running on with low forward speed. He doesn't go into detail about this part - does anyone know what happened in the actual flare / touchdown phase?

Following on from that, is the taught technique to run on at high speed (as might be appropriate onto a runway, for example, but obviously not out in the sticks)?

[Flap62]

No helicopter knowledge at all but the picture in the article suggests some element of run on.

[Lonewolf_50]

Quick question if anyone knows the answer - as I read it, the pilot in the article discusses how he didn't do an auto as per the standard training, but used a technique he'd developed by practicing in the sim until he could achieve a safe landing some of the time.

There's mention of not wanting to land at high speed (great idea); he also talks about getting the engines off (or to idle?) and achieving an autorotational state, taking control of the aircraft and landing safely as per this personal technique.

I assume what he's talking about is getting most of the forward speed off in a flare, then cushioning on as you normally would in a smaller helicopter, or at least running on with low forward speed. He doesn't go into detail about this part - does anyone know what happened in the actual flare / touchdown phase?

Following on from that, is the taught technique to run on at high speed (as might be appropriate onto a runway, for example, but obviously not out in the sticks)?
About 20 years ago, when I was getting Blackhawk training in the sim, the auto technique the old warrant officer taught to me included run on/fwd speed rather than any attempt to stop on a spot. I can try to find my old -10 and see what the paramaters were per standards: my brain recalls 20-25 knots A/S but I may be recalling a different number. (Will edit if I can find that reference).

[rjtjrt]

From the photo's in the article, looks like the aircraft was run on. Wheel tracks in the sand for quite a distance.
One photo seems to show other crew member just after he jumped out and shows wheel tracks as well.

[Tourist]

* although weren't the Sea Kings prone to transmission failures if they had an engine failure when hovering out of ground effect when doing things like mountain rescue? Something in my memory talks about it being very marginal and prone to over-torquing failures on the remaining engine, but I may have made it up

The problem in the Seaking and many other helicopters is not transmission failure once single engine so much as simply a shortage of power.

The power required curve for a helicopter is high power to hover, minimum at around 70ktsish for a decent size helicopter and high power again to go fast.

In the hover and light wind (even 15kts makes a huge difference) most/many twin cannot maintain a hover at a decent weight single engine.

Military SAR was allowed to practice without being safe single engine- ie in the event of an engine failure things were not going to be pretty.
In the Seaking we would brief the situation ie run and cut (winchman/SAR diver was going in the water immediately and we would attempt to gain enough speed to fly before impact) or safe single engine. I seem to remember 65% Tq was the magic figure.


The thing to realise is that rotary is very very different to fixed wing. There is an entirely different risk level at pretty much all times.

[Tourist]

http://i404.photobucket.com/albums/pp121/Tourist_photos/Reasoner.jpg (http://s404.photobucket.com/user/Tourist_photos/media/Reasoner.jpg.html)

[PDR1]

So the primary Safety Case argument is simply "If you can't take a joke you shouldn't have joined..."

:)

Thanks Tourist - it's given me an insight. I've spent most of my adult life on the design and support side of the fast jet community, and had a PPL-IMC before marriage & kids got my flying "correctly prioritised" (as my better third put it) 18 years ago, but I've only ever had 2 hours of rotary stick time (both in a piston Enstrom). If I won the lottery that might change, but I don't think it's going to happen any time soon.

PDR

[Basil]

Rivetting article!
I'd like to have flown rotary but they didn't fit in with my career planning; I thought large multi would transition better to civil. Having said that, ex rotary pilots I've flown with have the legendary 'Good pair of hands'.
I do have the plank attitude that they are, to some extent, the work of Satan and have only voluntarily flown in one twice; once before I knew any better and once to please a colleague who wanted to demonstrate how to get a 30ft chopper into a 25ft clearing (Well, that's how it looked to a slightly nervous Basil). Other occasions were by command ;)

[handysnaks]

PDR 1, I can't see that anyone has answered your original question!
The problem was not that the aircraft was unlikely to survive an autorotation to the ground but that it was unlikely to survive an autorotation due to and compounded by a tail rotor failure.
Apolgies if I missed a post that did answer the point!

[3 bladed beast]

Met this guy on a recent course.

Absolutely straight talking senior officer, extremely capable pilot and boss!

Quite refreshing really

[Arm out the window]

Thanks, Lonewolf - I never flew the Blackhawk but the guys at the same unit I was who did used to do reasonably quick run-ons to the runway to practice various emergencies.

Being in the skidded helicopter fraternity, we always went for little or no forward speed for an auto, and would run on to a flat surface at a not-too-excessive speed for some stuck pedal practice. However, I think with any kind of landing out in the bush on uneven or loose ground I'd want to get the speed pretty low no matter what kind of machine I was in, as long as there was sufficient cushioning power in the rotor system to get a relatively controllable touchdown at the end.

Just edited to add: the idea of a low or zero-speed auto for a non-functional tail rotor works for me - it's always a discussion point no matter what you fly, but I tend to agree with the point that it's going to be the forward speed and possible rollover that will get you; a reasonably controlled vertical impact even with a bit of turn seems preferable going into unprepared ground.

[Rotate too late]

Fair one, but I would make the point that a fully tooled up AH in Afghan was heavy....very heavy, therefore bringing it to a halt would have been a challenge in even the very best of circumstances. The ground before them was down to a good operational decision and pure luck. Some of those wadis would have utterly decimated that cab, no matter how good the flyer!
RTL

[The Cryptkeeper]

Rotate Too Late, spot on.

I was Nick's SQHI at 654 prior to this tour (I was leaving the mob) - an extremely capable pilot and OC.

Those of you that have pointed out a slight run on are correct, to achieve a zero speed auto in an AH into a dusty desert would be a miracle! It was quite simply an incredible bit of flying. The TADS footage of his stationary tail rotor from his Wing is eerie to say the least.

Just to clarify, no official training manual or RTS states that a safe landing from an auto after TR failure would be impossible! Experience in the simulator with the current flight model suggested it would be pretty difficult and advocates a high speed run on to maximise the effect of the tail fin of the aircraft to keep it straight - I think this is what his statement in the article is hinting at. Plainly a long run on in the middle of the Helmand desert wasn't a great option, hence the crew's thought process.

One of the great things I always found with Apache training is the idea that there are different ways to achieve the same outcome with all the systems - this tends to imbue in pilots the concept of, "It's a toolbox, you use whichever tools necessary to get the desired result."