Tailrotor failure - is it always unrecoverable ?
 

Newbie question here, so please forgive my ignorance.

All the tailrotor failures I have seen training videos of, invariably seem to show a high sink rate often accompanied by a spiralling nose down attitude until impact.

Is there a best practice recommendation for cyclic and collective use in such a situation, or are you really just along for the ride at that point?

I'm sure you'll get plenty of answers from the professionals here, but even as low-time heli pilot I know it's not unrecoverable - though when it happens IRL it may be a bit of a shock, like any emergency.

You can enter autorotation, supposing of course you have somewhere to go. Or in the R44 (yes, I know), and I guess most other types, you can fly in a peculiar feeling slip at about 70 knots until you can find somewhere safe to autorotate to.

This is when your instructor has spent half an hour prepping you for the exercise, then counts down before putting the pedals in a more-or-less neutral position. How it works when the TR suddenly parts company with the airframe, or the drive snaps, is another matter. By the time you've realised what's happening, instinctively tried to counter it with pedal, realised it's getting worse, had the "aha! TR failure" light bulb go on, and dropped the collective... you'll be going round quite fast, so your reactions may not be quite that good.

A loss of tail rotor thrust is all about the balance of torque and anti torque. In normal flight we have some amount of torque applied to the main rotor, and we supply the anti torque from a combo of tail rotor thrust, and the stability that comes from the vertical stabilizer. When the tail rotor fails, we must either have enough speed to allow that vertical fin to offset the torque, or we can reduce the torque to the main rotor so that the airspeed can help offset. The absolute fastest way to reduce torque is to lower the collective. By reducing torque this way, we leave the engine fully functional and available, we just remove the torque by reducing the rotor drag. We are then free to increase speed to a point at which that vertical fin can offset torque. then the pilot increases main rotor torque and flies away to a safe run on/ forced landing. If this balance is lost, the aircraft will spin... at that point, it can quickly become a ride along.

It largely depends on what fails and how and where.
If a driveshaft fails, or there's a gearbox failure, you could potentially also lose part of the tail. In this instance the change of CoG could make the aircraft unrecoverable.
There's theory and there's reality.
It's always better to not stick the tail somewhere it doesn't belong, since that seems to be a leading cause of "loss of thrust".

Army AV8R I think your explanation is spot on and very clear. Might I add some value to your post by saying, the amount of "Thrust" (antitorque) available at a specified IAS by the Fin/Tailboom varies considerably as a result of the design. I.e. fenestron fins tend to provide a lot of thrust.

And of course, the lower the IAS when the event happens the more height needed to achieve an IAS whereupon the Fin thrust can be exploited.

Sadly we tend to be at Low IAS during approaches and departures where height is often insufficient to effect recovery.

This post and AV8Rs relate only to a loss of tail rotor thrust. (All the physical components remain on the Helicopter). Flight Manual procedures generally only provide guidance for this type of failure.

As Bell Ringer points out, if a lump of mass departs the airframe at the end of the tailboom the effect on the CG could cause departure from controlled flight. The TR and its GBX are a long way from the rotor centroid so not a lot of mass needs to depart to create this loss of control. For this reason I am not aware of any flight manual that provides a solution for such a condition.

Hope this helps the original poster.

http://www.pprune.org/military-aviat...ssue-19-a.html

FYI

Fonsini - the immediate survivability depends a lot on your height and speed at the time of failure - a low hover or highspeed, high altitude flight should, in the initial stages, be very survivable. Having said that, it depends on whether you identify the nature of the failure quickly and correctly, especially in the low hover.

Altitude and airspeed are your friends when dealing with a TR failure and you may be able to establish a power/airspeed/sideslip condition to allow you to transit to a safe area for EOL or, on some types, a fast running landing.

The EOL may in itself be an interesting one since you have no yaw control and, as you decay the Nr by pulling pitch at the bottom, the aircraft will want to yaw. The friction of the skids on the ground will help keep you pointing in the right direction and a crosswind can make things easier still.

Low speed, lowish altitude failures are usually the worst - if you can gain speed without spearing yourself into the ground then it may help you regain directional control. The worst condition would be a still air hover at 100 -500'.

And besides "loss of tail" (with loss of CoG) and "loss of tail rotor thrust", you can also experience "loss of tail rotor control". In this third case, you usually will be able to fly along with the help of the vertical stabilizer and then make a running landing on any surface. This can easily be trained. Just get off the pedals and enjoy.


It gets tricky when it comes to "stuck pedal" (either low power stuck or high power stuck).


Thracian

Another problem with a drive failure in forward flight is that the tail rotor will go into autorotation. This could lead to flapback and large pro torque moment. The only way you can overcome this is to enter autorotation.

With old helicopters like the S55 and S58 you could get away with finding a power/speed combination to either a fast run on or an autorotation to the ground. Modern helicopters, especially those with a stabilisation system, don't have the aerodynamic qualities to continue flight so you are committed to landing fairly rapidly.

Probably a pilots worse nightmare.
Probably the least practiced malfunction (for obvious reasons).
Probably the least understood malfunction.
Probably a helicopter's achilles heel (unless you're NOTAR).
Probably not a lager, then................

http://www.pprune.org/rotorheads/422...+rotor+failure

Enjoy.

TC

Notar has a TR but it is hidden in the tailcone ! The shaft and straps can fail !

I didn't realise this while practising it during training, until considering that it's always practised at height, with sufficient forward airspeed.

The discussion the other week about the "pumping" of the collective if experiencing TR failure in the hover or taxiing was a good clue as to how little the typical PPL training covers this problem.

In the hover or hover taxy, if you can recognise it, reduce the yaw (lower the lever and or close the throttle - twist grips have a distinct advantage here) and cushion the touchdown then you should survive it.

that's because it can be very dangerous so best done in a simulator if you can get in one.

First, you have two know about the main failure about Tail rotor :
1/ lost of control = pedal, cable, anything change the pitch of the blade but blade runing always
2/lost of part or totally Tail rotor : driving shaft, blade, tail gear box =blade no more runing properly.
Two cases totally different to manage, but you have to identify what happen first..
in case 1, you only lose the "pedal" control of your tail rotor, that'is the simpliest case. Take a look on your T/r if you can to understand whathappen, then, take your time, choice a big and flat safe place to land. On most of the helicopter manual, they say "Perform autorotation". It's trus, but you have another way : make a very flat approach, accept the yaw and keep the nose be to the right or left (depend the rotor clockwise or not). when you are nearly to the touch down low rate of descent low speed, apply slowly the pitch to put the nose "on line" with the frame and slide slowly until stop. Then put the pitch down, shut down and go to the Bar drink a Beer....
In the case No. 2, it's a little more creepy. i got a training by a pilot who's had experiment IRL .. on after the training, it and i'm not sure to do the same thing if happen really to me...
So, when you lose part or totally of the blade the CG change and you lean and you have the nose to go down . All of that happen fast...very fast.
At this time, reduce the speed if needed. Remind that to go straight and maintain altitude, you have to admit the bank and the nose down Take your time ( not too long, you don't know if the T/R maybe destroy the rest of your tail...) to choice a really good place to perform an autorotation...And do it......BUT, you have to know something : All your instrument byair managed are totally false ! Speed/rate of descent/ altitude..The bank and the nose down change the wind in the static plug and dynamic.. So if you have a GPS or another electronic system, trust him for the speed...If not : trust yourself for manage the speed, your rate of descent and perform your autorotation.....Good luck....
I never see this procedure on any manual and nobody train me on , except a old Jungle pilot who's experiment that the sling rope and the hook bump and destroy his Tail rotor. Thanks to him ;)
Sure, to explain the both procedure i take the best case : some speed, and not to close to the ground...
If no speed, try to gain some speed to put some air on your fin and be little be "online" to perform case 1 or 2.
If close to the ground, look like final approach, ( i had experiment it IRL ) PITCH DOWN ! if not you make the weathercock very fast.. It's better to crash on your skids than turning until not controlled crash...

Making "absolute" statements. Where generalized comments are more appropriate would be a better approach to this.

Example...a Gulf of Mexico event where a Bell 412 had a total upset at night due to a tail rotor failure in cruise flight.....the Crew regained control and successfully landed the aircraft.

It is not the presence of SAS that determines the outcome but rather the ability to match weather vaning effect to main rotor torque by reducing Collective and reaching an airspeed/Pwer setting that allows that.

The biggest hindrance probably is far too many helicopter pilots just do not understand the interaction of the flight controls and rpm control and the affect they can have "Torque" applied to the airframe.

As there are many different kinds of tail rotor failure....in all kinds of situations....in all kinds helicopters....there can be no single response.

The key training issue is to explore control reactions in controlling "Torque" without use of the Tail Rotor.

Also....one has to grasp the fact "Green Arc's" are for NORMAL OPERATIONSand there is nothing Normal about dealing with a tail rotor failure.

One has to be able to instinctively react in some situations and then be able to follow up with learned concepts.....and doing whatever it takes to control the aircraft.

I have had one tail rotor failure at a hover....we landed with no damage.

I have had one Stuck Pedal situation in flight....and landed safely.

I attribute both to the quality of training I received in the US Army.

We did lots of practice in Huey's....and got to see the effect of the controls including throttle. I used those same techniques in other aircraft I flew later.

I have some key takeaways from your responses that I had not considered. I suspect that many pilots instinctively pull on more collective during a TR failure, exacerbating the spin and loss of control. I fully understand why perhaps only the military routinely accept the risk of training their pilots to deal with such an emergency, as it is far more likely to happen when people are shooting at your aircraft.

Gold standard information as ever - thanks guys.

I agree with SASless, I make my training in the French Army and we perform all kinds of T/R failure....Training is the key ;)

When teaching TR malfunctions just keep it simple. There are 2 types. Loss of drive. Loss of control (stuck pedal, broken cable, jam before or after mixing unit). Easy to diagnose which is which. Loss of drive gets your attention immediately. Loss of control you might not notice at all initially. Loss of drive = lower collective, autorotation, shut down engine/s before the landing flare. Loss of TR control, the technique is the same whatever is causing the problem. Fly at 60-70 kts adjust collective until the ball is balanced and note the power (this will be very close to the power at touchdown). If ball centered with high power, lucky, expect slow speed run-on or hover landing. If low power, bad luck, expect a faster run-on landing. With nose left of centre and aircraft aligned with runway reduce speed to 45 kts just before touchdown but don't land. Fly level 5-10', slight flare to slow down, as the aircraft slows down it will descend, but don't let it land. Slowly increase power whilst flying level and continuing to slow down (the nose will come right as you increase power). When straight, keep that attitude and power setting and the helicopter will continue to slow down and land itself. Do not let the nose go right of centre (for anti-clockwise main rotor, eg Bell). Keep it straight during any ground-run with throttle and some opposite cyclic. That's it, easy. This technique will work for most helicopters.

As long as the TRGB or components haven't departed the scene and put you out of CofG limits, and you have a suitable landing site, you should be able to land without a scratch. I've practiced this many hundreds of times. The key to stuffing it up is letting the nose go right of centre when you're close to the ground. When this happens students tend to react by increasing power, and when you do that it very quickly becomes unrecoverable and you'll turn it into a mangled mess.

Gullibell - you should also stress how helpful a crosswind from the (left in your case) is as it helps keep the nose from swinging right for longer and gives a slower touchdown speed. The bigger the fin/vertical stabilisers, the more effective this becomes.

F.E.D. re your post #9. I can add a historical data point.

During initial commercial S-61 FAA testing at the forward CG limit, the test crews had trouble making the required control delay time after a forward AFCS pitch channel hardover at max power, min speeed ( 40KIAS as I recall ).

The Ch Exp. Pilot got involved and went out to get the data point. Set up the condition right after takeoff, hardover was introduced and nose went down.....and down. Well, the aft stick input was finally made ( with authority ), easily meeting the required delay time, but the tail drive shaft suffered an intervention by a main blade, and an autorotation into an open field with 2 inches of snow resulted. A picture exists showing a perfectly straight line thru the snow made by the tail wheel. Instrumentation indicated a tail rotor Nr that could only be explained by autorotation.

So, the tail rotor autorotative state may not be all bad. The copilot for the flight was Dmitri ( Jimmy ) Viner for the historians out there.

My personal soapbox. Why do we insist on calling completely unrelated malfunctions virtually the same name? Tail Rotor Drive Failure versus Tail Rotor Control Failure.
In the heat of the moment, it's easy to jump down the wrong rabbit hole. I've seen multiple crews open up the cards to the wrong section and start the wrong drills because of this.

My suggestion; Tail Rotor Failure = Loss of drive/TGB detached

Yaw Control Malfunction = Stuck/Sloppy pedals.

Simples

Often because they are not as familiar with the cards as they should be.........I have seen the same for the same reason

This makes interesting viewing

https://www.youtube.com/watch?v=fNkwk2d_DJ8

Agreed Crab. But a simple change in nomenclature from the outset would effectively stop any confusion before it has time to start.

I can't remember what the latest flight safety just culture management buzzword this kind of thing fits into, but there's got to be some systemic failing. We have for years, collectively, set up a man trap that we repeatedly see crews fall into, but don't do anything about it. Stating that people should be more familiar with the cards/drills doesn't fix anything.

Well, looking at the title of your post, if all tailrotor failures were "Unrecoverable" there would be no Emergency Procedures called for. Just as there are no "Wing Falls Off" checklists in fixed wing nor "Loss of Main Rotor" in helicopters.
There are procedures that must be carried out...initial actions are "Memory Items" Reaching for a checklist as you spin like a Kid's top will not lead to a optimal outcome.
You must be fully aware of the initial actions and carry them out.
FYI I had a friend who had the tailrotor and gearbox of a Hughes 500 depart the airframe in cruise flight ..he got it down OK ..his underwear and seat cushion were unrecoverable!

A Twin Squirrel landing after a TR drive failure. Not good quality video, but the stationary TR can be seen.

I recall a Met Police Bell 222 had a TR failure around 1980 and made a run-on landing at Hatfield. I think it rolled over but all walked away.

Jellycopter - I just think it is down to training - and that includes knowing the cards through self-study and practice in the simulator.

I think the difference between a TR drive failure and a TR control failure is quite clear, perhaps because I have taught it quite a lot.

TR drive and TR control failures were mandatory parts of the 6-monthly sim on the Sea King as I am sure they are on many other types.

I don't know what you would call the two conditions that would be any clearer.

Crab, if I had a Euro for every misguided helicopter pilot that glibly stated that they'd autorotate in the event of a TRCF I'd be quite a bit better off than I am now.

If you turn the problem through 90 degrees, no one ever gets the drills for stuck collective mixed up with MGB/input drive failure. But we're talking, effectively, the same thing. Why do less well trained crews continue to make the same mistake?

The fact that someone on this thread decided to bring stuck pedals/TRCF into it shows the depth and universal nature of the problem.

I wish, for the good of Rotary aviation, people would stop using the term 'Tail Rotor' when referring to a control malfunction. Call it what it is, a Yaw Control Malfunction.

Because that is what they are. It is not possible to be confused which of the 2 you have, whatever you care to call them. They are so obviously different malfunctions.

TR drive failure don't even bother getting out the emergency checklist, the immediate actions are all memory items. If it's an impending failure e.g. vibration in pedals or airframe, TGB/IGB chip light on, grinding noise etc, but you still have pedal authority then sure, turn towards a suitable landing area and get out the ECL and review the procedure. Maintain height, slow down to best rate of climb speed. Do not descend until you arrive at a point in space where you can execute an autorotation to the landing area.

TR control malfunction there are no memory ECL items, this is a far more sedate problem to deal with. You have time to get out the ECL. The next thing is put your test pilot hat on and diagnose the problem as per the checklist. But as I said before, it doesn't matter whether stuck pedal, broken control cable etc, the landing technique is the same for all of the causes of TR control problem.

Whether TR drive failure or TR control malfunction, if you have a suitable landing area to aim for you should be able to execute a safe landing without putting a scratch on the aircraft.

One could always ask the TOLL Chief Pilot on the NSWA AW139s if a tail rotor strike is unrecoverable. By all accounts, they did recover, but by truck to Bankstown!

As the OP on this, I really was only referring to tail rotor failure in the sense that it has failed completely for reasons of a broken driveshaft or blade failure or hub/bearing failure etc etc.

This video would best illustrate the failure type I was thinking of - with the best video quality I can find showing the TR condition. I also chose this as the pilots survived the forced landing.

I find it hard to believe that it is possible to confuse the two malfunctions too. It shouldn't be possible.
However, after decades as an instructor and examiner I have had many pilots that have. I believe that when pilots give either malfunction the 'tail rotor' label all too often they opt for the dump the lever option when it's exactly the wrong thing to do.

Crab has experienced the same. Are there any other instructors/examiners out there that have seen this from time to time?

I remember Dennis Kenyon demonstrating Tail Rotor Failure recovery whilst doing his display at an airshow at Cranfield in the 1980s. He was flying his normal, excellent, display in an Enstrom when something "went a bit wrong"! He then flew a couple of low passes down the active runway and, on the third pass, did a run-on landing. Everything was OK - apart from the broken TR cable!

Palma - that is exactly what Jellycopter is talking about - it wasn't a TR failure, it was a loss of TR control.

It is straightforward, with a TR failure, the TR is producing no thrust in any direction and probably not turning at all. With a TR control failure, the TR is still turning and may be producing thrust one way or the other, depending on the nature of the failure, or none at all if it has gone to flat pitch.

I never understood the obsession with tail rotors.... Just fly a tandem rotor, at least then all the bits that can break aren't in places where you are going to put them into a tree...

Except that hitting/losing one of those rotors is guaranteed to be catastrophic:ok:

Karma. Toll was reluctant to let me do any training in their NSWA AW139. They got to bend one first with their own people before I ever got close to one.

Confusion reigns for many recurrent trainees when diagnosing TR control malfunctions. But for TR drive failure they don't have time to get confused before they need to carry out an immediate action in response to their predicament. What that immediate reaction is can be surprising...I've seen a pilot just take his hands off the controls and leave the outcome of TR drive failure entirely up to the will of Allah. Needless to say it didn't end well.