TR Failure Drills

[ShyTorque]

With my QHI hat on, having been a member of the forum for many years, a question for the rotary pilots out there.

We talk about engine failure scenarios until the cows come home BUT...

Are you confident about your ability to deal with a tail rotor problem? Could you recognise the difference between a loss of TR drive and a loss of TR control? Do you understand the theory and the recommended procedures for your aircraft? Do you think you know enough and have you practiced different scenarios?

[Staticdroop]

We had this subject brought up in our company regarding both PPL training and commercial pilots line training. I can recomend the video produced by Bell using a jetranger to demonstrate the various types and the subsequent actions.
It is a subject that is ignored and more should be done to teach the drills required.

[SASless]

Shy....


You ever experience an actual Tail Rotor failure?

[ShyTorque]

Thankfully so far only in flight simulators.

Roofus has had two real ones. Is he still around?

[FlyAnotherDay]

TR problems weren't much mentioned in my UK PPL (as far as I remember) certainly never taught, but I was subsequently taught TR jams when I asked in NZ.

Theory, I understand. Recognise the difference between loss of TR & of control? - yes. Recommended procs - R22 FM only mentions loss of TR thrust, not jams, but what I was taught for jams works as far as I got to try - I'd like to be able to practice to the touchdown and run-on. Know enough and practiced enough? If I have time to work out what's happened and actively think about it, so I guess that's a 'could do with more practice'. Confident to deal with a TR jam? - errrrrr, yes, moderately, in flight or hover, but not on take-off or landing.

[Whirlygig]

Are you confident about your ability to deal with a tail rotor problem?
Well, I think I would come out of it alive but they couldn't use the aircraft again.
Could you recognise the difference between a loss of TR drive and a loss of TR control?
Hmmm.... possibility not. Good point.Do you understand the theory and the recommended procedures for your aircraft?
I understood them at the time :uhoh:
Do you think you know enough and have you practiced different scenarios?
I never know enough but, as part of my PPL, my instructor decided I needed some extra-curricular activites; tail-rotor failure being one of them (collective jamming being another). I am surprised that it is not part of the PPL syllabus and, to be honest, I didn't find the techniques any more difficult or buttock-clenching than engine-offs.

My PPL instructor was a hard task master but I am now glad that all sorts of emergencies were practiced on a regular basis. He still does it if I need a 28 day check ride :rolleyes:

Cheers

Whirlygig

[Nigel Osborn]

Guys & Girls

I can't believe you don't immediately know the difference between a TR drive failure & a control failure. If you don't, please ask someone before it happens to you as there is not much time to whistle dixie if the drive fails. Handling procedures are quite different for both problems & easy to practise.
I don't know how to find it but no doubt some of you computer boffins can. Try looking up an accident that occured to a Bell 47 over Sydney harbour back in 1966 or 1967. All 3 on board were killed and the whole thing was filmed from the ground and by the cameraman in the Bell, truly incredible footage which clearly shows what happens when your tail rotor has had enough.

[Whirlygig]

Nigel,

I don't know of the incident to which you refer but there was a case of a squirrel (last year) at Chicago (?) whose tail rotor failed. This was also videoed and the pilot made several go-arounds before he felt happy to do a run-on landing. All walked away. This scenario would only be limited by the fuel you have on board.

Cheers

Whirlygig

[ShyTorque]

Nigel,

I completely agree with your sentiments. The Sydney Harbour film was shown to all students during RAF training, possibly still is. A drive shaft failure as I remember, the pilot seemed not to autorotate, hence the complete loss of control.

Whirlygig, was that one a drive shaft failure or a control failure? I would be surprised if it was the former if it was possible to go around.

[Nigel Osborn]

ShyTorque

A bolt holding the pitch link broke allowing 1 tail rotor blade to swivel. This lead to that blade flying off into the harbour. This lead to a massive balance problem which caused the other blade and the gear box dropping off into the harbour. This sudden decrease in weight at the rear tip of the 47 caused the forward c of g to be at least 12 " out of its forward limit.
Jim was hovering at around 1000 ft and started to spin straight away. Whether he autoed or not, he now had no practical control of the 47 but as the rotor rpm looked good and as he was an ex RAF pilot, we all believe he did but as I say, it didn't matter anyway.
Incidently his wife was cooking lunch for him on a fine Saturday morning, when the media phoned to ask her what she thought of her husband's accident!
Another ex RAF pilot had the gear box and TR drop off in his 47 in the cruise but this time it swung on the tail rotor cables. The 47 pitched up as it swung back and pitched down as it swung forward. He entered auto and by shear a**e it levelled off as he touched down on a gravel bank in the river Gordon in Tasmania!!
He ran out of fuel in PNG a few months later and killed!

Sorry rambling on but I used to fly for that company.:(

XE
Yes, TR drive failure = engine failure
Control failure NO

[Ascend Charlie]

We (in Oz) always taught jams, loss of control and loss of drive to all our students, commercial or private, and they nearly always went to touchdown. Only power terminated if Bloggs let it get away from himself at the last second.

A marvellous way to learn control of the aircraft and develop a "feel" for it. The most important thing we drilled into Bloggs' thick skull was:

DON'T LET THE NOSE COME UP!

By keeping the nose down, there is control of the speed and rate of decay of speed. Nose up, speed comes off fast, haul on collective to stop ground impact, nose of helo zips off to the right and you are in trouble.

Last year at FSI in the S76 sim, we were practicing tail drive failures. Crash Buddy elected to auto to the ground, and we would have survived. For my turn, I nosed over for speed and with some manoeuvering managed a smooth run-on at the nearby airfield, much to the surprise of the sim instructor.

So, for you junior QFIs, find a senior one who will run you through the scenarios to touchdown, and then pass it onto your students.

[Helilog56]

:ooh: I have managed to endure two seperate t/r failures over 27 years. Henceforth whenevere I am instucting or working as a training pilot the personel experience is great to utilize as a trainig tool. In Canada a lot of emphasis is put on t/r jams, loss of t/r authority and loss of t/r effectiveness. Any and all companies in any part of the world, and doing all types of work should positively be doing this also....Trust me, when (not if) this happens to you, you will be thankful if you had the training...;)

[Hummingfrog]

Nigel and XE

"Tail rotor drive failure does not equal engine failure" is too simple a statement.

In the helicopter I fly - AS365N2 a tail rotor/fenestron drive failure, unless in the hover, is not an enter auto immediately scenario. The large fin is designed to offload the fenestron in the cruise so directional control should be fairly easy to maintain.

The tricky bit is landing as a combination of airspeed and power needs to be found which keeps the a/c from crabbing as it touches down. In the Dauphin's case a wind from the right helps.

Don't expect to land off your 1st approach as this should be used to assess the airspeed/power combination. If it looks wrong go around early.

Once you have got the airspeed/power combination right fly the helicopter like a fixed wing with a threshold speed of the airspeed for zero yaw + 5kts

Once on the ground don't relax and lower the collective or you will find yourself leaving the runway as the yaw will develop very quickly. Keep the collective in the same position you landed with and shut down the engine(s). This removes the yaw and allows you to keep straight with brakes

My company encourages us to practise this and it can be "fun":uhoh:

HF

[ShyTorque]

Good replies!

I think it prudent to remain a little wary of simulators as the ultimate "gospel truth" for this type of failure because of the way they are programmed.

A manufacturer cannot test the ultimate aerodynamic behaviour of his aircraft's response following tail rotor malfunctions / failures in any great depth, for obvious reasons. A "best estimate" response is usually programmed into the software for cases like this, which are known as "off model" situations.

What sims are really great for is to teach understanding of the different types of TR malfunction and developing a strategy to deal with them.

[Thomas coupling]

Whirly: If you don't know the difference between a TR drive failure and TR control failure, I suggest you go back to school before your next flight:ooh:

I would suggest 90% of the helicopter fraternity do not practice nor discuss TR problems in sufficient depth. For many it's put in the "too difficult" box.

It would be interesting to learn whether there is an increased incidence of TR failures/control failures than engine failures.

I know which I would prefer:\

[ShyTorque]

For those pilots with an hour to spare, take a look at this CAA paper.

http://www.caa.co.uk/docs/33/CAPAP2003_01.PDF

Appendix B (at the end of the document) is very useful pilot reading.

[Banjo]

One of our Pilots has been un-lucky enough to suffer two tail rotor problems in the last 4 years. One was a failure in the hover following FOD intake the second a pedal jammed on full deflection. He was fortunate enough to walk away from both; the second incident didn't even damage the A/C.

We teach tail rotor problems all the time as it is as important as engine failure drills if not more so. I have to say I don't want either but given the choice I’d prefer the donkey to stop over a tail rotor problem.

As mentioned here already should the TR gearbox rip itself off that mass of metal on the longest arm on the A/C can put you well out of CofG limits and loss of control is the result. Should you react to the pitch down moment with aft cyclic you will only chop of more of the tail boom which will do nothing to help the situation.

As an aside there was a thread on here a while ago on would you land with a chip light or carry on to your destination. The more experienced pilots who have been used to many spurious warning lights over the years seemed to favor the carry on option. In light of the above paragraph I always choose to land. the physical lose of the T/R gearbox which can follow a seizure normally has only one drill for the pilot to follow and it involves putting his head between his legs and kissing his a**e goodbye.

Another consideration is how many engines the A/C has and are you the only pilot or flying multi crew. In most singles the throttle is on the lever and you can control the rate of yaw and "steer" during a run on landing. Failure in the hover allows you to close throttle and take needed action. If however you are flying twins most have a quadrant in the roof which makes power control during run on landings un-workable unless you have two crew who have practiced for such a situation. Does anyone train for this?

Remember also the engine and main rotor RPM considerations if you lost tail rotor drive as all that drag is lifted from the system. If this happens in the hover and you fail to react quickly you will not just be carrying out a spinning tail rotor failure from low hover but will probably find yourself at some height due to the increase in main rotor RPM. This happened to a gazelle a few years ago and the climb to height was impressive due to the throttle being in the roof and the pilot unable to close it quickly.

With PPL students to save them from having to think when under the pressure of a run on landing we teach the simple trick of steering with your little finger. While holding the lever uncurl your little finger and point it at the floor of the AC. now which ever way you want the A/C to point as you run over the ground point your little finger in that direction. No good if the rotors are French but then they seem to place the throttle where you can't use it anyway i.e. single squirrel and gazelle.

All in all I just hope the little thing at the back keeps spinning fine for the rest of my flying.

[ShyTorque]

"If however you are flying twins most have a quadrant in the roof which makes power control during run on landings un-workable unless you have two crew who have practiced for such a situation. Does anyone train for this?"

Yes they do.

[SASless]

Pedals stuck in the "power applied" position should be no big deal....being of the generation that learned how to manipulate the throttle on the collective....I understand all that theory. As I got older....and got more lazy and probably beginning to suffer from alcohol induced memory loss.....I find simply reducing Nr to the minimum I can stand....and landing the helicopter a lot easier. The only way to reduce the excess tail rotor thrust for the collective setting is by slowing the tail rotor RPM thus making it produce less thrust....as I see it. Make a shallow approach...hold your airspeed up....get to a foot or so off the runway....decelerate slowly....until the nose aligns with the runway or you come to a hover...then set the aircraft down. No fancy thinking which way to move the collective and/or throttle.

In that I have flown both lefthand and righthand turning rotor systems....I had to settle upon a common method for that....thus power foot forward....no big deal. Power off foot forward....takes a bit more thinking.....

Recently.....I was indoctrinated into the "approved Euro way of handling BK stuck right pedal situations". It was done at night on NVG's.....and the solution being extolled was to find an airspeed that allowed the aircraft to streamline and then land at a fair old clip using collective position to align the nose of the aircraft with the runway whizzing by at 80-90 knots. This method I found altogether uncomfy and suggested I would be more comfortable doing an engines off autorotation to the runway. I feel rolling over on my side or something at minimum ground speed and all power off would be more desirable than running off the runway in the dark at warp speed and full engine power applied to the rotor system when it hit paydirt.

In US systems....left foot forward is good news....right foot forward calls for some airmanship.

One man's opinion anyway!:ok:

[NickLappos]

SASless is right on:

TR stuck at Big power is easier than low power. Reducing the RPM is double magic. The tail thrust drops by the rpm squared, so 90% Nr means the tail rotor is down to 81% of max thrust (.90 x .90). Also, the main rotor torque goes up by the rpm drop, so the torque required to hover goes up by 10%, which means more tail thrust is required to provide the anti-torque. The combination of tail thrust down and main torque up is almost perfect to absorb the max tail rotor angle.

TR at low power, or loss of thrust is different. Whatever you do, start from autorotation and end up in autorotation near touchdown. When the nose swings, and you therefore know thrust is lost or stuck low, get near/into autorotation. That is a safe place to be at, and what you should do when you diagnose the problem. If you can stretch the glide while coming home it might be worth a crack, but do it by slowly adding power from a nice trimmed autorotation. Don't mess around and lose that nose-in-front-of-tail thing, because once you get too slow and have too much right (or left) thrust, your goose is cooked, in a spinning fashion.

How do you try to stretch your glide or fly home with a right thrust situation? from a trimmed auto with a landing spot picked out (your escape route) try raising the collective a little. Keep your feet flat on the floor as all that silly pedal pushing will just frustrate you and allow you to forget the situation (because you will be pushing on them and re-learning what TR failure means). As the nose swings right put in left roll to stop the turn rate, and push the nose down a bit to prevent speed loss. Pick a speed about half way between best climb and best range (maybe 110 knots on a fast helo, 90 in a slow helo). Beedy-eye the speed, do not let it decay! Note speed, ROD and roll angle to keep from turning. As you raise power, you will force more sideslip, needing more roll. It will be screwy, and you will feel very insecure (if you have any brains at all, very insecure). If the nose seems to want to break all the way to the right, just drop the collective a bit to control it. Up collective is right yaw, down is left. With some luck, you can stretch your glide a big bunch. A light weight helo can be flown at a very flay angle of descent if you keep the speed up.

If you halve your ROD, you double your range to touchdown, and you increase the number of landing areas by 4 times (more area to pick one out in). At the bottom, just flare the nose up, drop collective and you will be in auto. Burn off the extra speed to get th best auto speed, then stabilize in the auto and make the landing.

All this fly-home theory is nice, if in doubt, just enter auto at the start, and forget the test pilot stuff, autorotate to a landing. Keep your speed up a bit right till touchdown, as you want the slipstream to help the fin keep the nose behind you.

[muffin]

How nice to have a safety discussion that is not about engine failure for once. Thanks to the original contributor for raising this topic.

Certainly during my PPL training all the emphasis was on engine failure and autos but the whirly thing at the back was hardly ever mentioned. I do think that there should be more time allocated to this during training.

Keep the discussion going guys - I am learning a lot.

[ShyTorque]

Nick,

A question regarding reduction of rotor speed. The minimum RFM figure for N2 / Nr on the S-76 is 93%, how would reducing it further, for example to your figure of 90%, affect the aircraft mechanically?

What about the engine to transmission torques increasing as the Nr is reduced for the same power? Is there likely to be a problem with breaking something else?

[Dynamic Component]

I would be very carefull on generalizing on what a "tail rotor control failure" is:confused:
In ze french FMs(EC120) it talks about "tail rotor control failure", but seems to follow the procedures of tail rotor drive failure(Auto)

This could confuse dumb pilots like myself:}

[NickLappos]

Shy,

Good questions, and important ones.

generally, no parts will fail for a 10% overtorque (at least on the helos I have deep knowledge of). Remember, this is a very broken machine you are flying home, and when you land safely, and get down from the shoulders of your passengers who have been carrying you around singing "For he's a jolly good fellow" with true passion, you can write up the over torque! A few seconds on touch down are no sweat, IMHO.

For the rotor rpm on touchdown, most helos suffer those transients on HV engine cuts, and touch down at somewhere around 80 to 85% rpm as part of the certification testing. We have to show the FAA some reasonable data to show that this is not a catsatrophic event, so we know that is ok.

If you ever saw "The High and the Mighty" then you will understand what I am discussing. The old former captain, now a washed up co-pilot, brings the crippled airliner back across the Pacific by vastly over boosting the remaining two engines, knowing he is damaging them, but also knowing that his fuel consumption is now low enough to let their fuel last to shore. He has to smack the young, by-the-book captain to make his point. Sometimes the limits can be "reinterpreted a bit" in a true life and death emergency!

Here is that clip, which illustrates my teaching style, the one I learned from SASless:

http://www.s-92heliport.com/highmighty.wmv

[SilsoeSid]

Interestingly enough, IMHO, no-one has yet mentioned the actions required for the MD 500/600/900 series of helicopters.

I think that zxcvbn would need to reconsider his theory.

[NickLappos]

The NOTAR aircraft have a tail rotor, it is inside the tailcone, out of sight (and better protected, to be sure!)

The types of emergencies are the same, I would imagine, because the fan, its shafting, the control system for it, as well as the nozzel control mechanism are all subject to Mr. Murphy and his Law.

SilsoeSid you are also right to call into question the idea that an autorotation is the cure for all tail rotor failures. At high tail rotor pitch failure, an auto is the worst answer, possibly leading to loss of the machine (to say nothing about its occupants!) This is especially damning when, with a TR control failure to high thrust (so called "stuck left pedal") you could fly home first, and make a powered landing.

[SASless]

Cor! Nick finally admitted he learned something from me! But then with my applied psychology who would not learn!

I prefer to call this method "The Pentacostal Method" in that its core belief is the "laying on of hands" results in the most effective rate of of learning.

It definitely is more fun teaching this way than by mere Rote learning. Primacy, intensity, effect, and exercise are all enhanced by such a technique.

One caution however....never use this technique on people who have arms longer than yours, who enjoy pain, carry guns, knives, dirks or daggers. Otherwise, the post flight de-brief can get a bit involved.

;)

[cpt]

Very interesting thread.
Did you ever consider putting all of these tricks in a book Nick ?

[Red Ant]

Some help guys, this is my pattern of thought when faced with uncommanded yaw or loss of tail rotor control. I would like some input and suggestions on safer/ perhaps more efeective methods

- TR control failure : high pitch angle(TR) , set up approach with nose yawed off towards retreating side of disc, by decreasing collective pitch, test speed at which nose aligns with direction of motion at safe height(500'), approach long flat smooth surface for a run-on landing, get within a few feet(safe tail rotor height clearance ) of the ground and slow down and thus incr. collective untill nose straightens out and run-on to ground.

- Neutral pedal(control system) stuck : similar but higher run-on speed. and the more it leens toward minimum tail rotor pitch stuck, best to enter auto/ semi-auto and do slide/run-on.

- Complete loss of tail rotor thrust/ tail rotor blades/ gearbox failure etc. I was tought to enter autorotation and do heigher than normal flare and then try to flare off all speed before cushioning onto ground. With the bigger twins (10t+ ) higher inertia will alow possibly a bit of yaw towards retreating side during flare before sink starts, thus a run on perhaps possible (gearbox drag). Once entered autorotation and sufficient height and time, inc speed to manuf. recommended V for loss of tail rotor thrust and start to increase coll pitch and correct with bank, as mentioned by 'NickLappos', but down to what altitude would you follow such an extended glide to (agl) before entering full auto again ? and also what sort of flare would be best for small and large heli's ?

Any replies appreciated greatly guys:D

[SASless]

One other thought....

I prefer to fly the aircraft with an aft CG vice loaded way forward. Seems the aircraft handle better when loaded aft and a secondary thought of positively affecting the CG shift should the TRGB and rotating bits depart the aircraft. Maybe it is just that I like to recline in my cushy seat rather than hang in the straps all day.

[Red Ant]

How Bad would the, or should I say is the forward movement of C of G with loss of the gearbox ?

[ShyTorque]

RedAnt,

I don't think there is a "blanket" answer. Each aircraft has slightly different characteristics and the multiple failure modes cloud the issue. There may also be more than one way of flying the aircraft to a safe landing.

My own main strategy for a TR control failure is the same as your own, namely to aim to get the nose out to the retreating blade side for approach which allows a gentle tweak on the collective to bring the nose straight whilst cushioning the landing.

This has been proven to work for both clockwise and counterclockwise main rotors from my own experiences in a number of different simulators (my own personal practice and also instructor duties). If there is no pressing need to land, I would consider a dummy approach or two at altitude to discover what will work best.

There is an obvious trap for pilots who fly different types, with opposing main rotor directions - it is possible to become confused about what is happening with regard to yaw directions, especially as during a complete rotor thrust loss situation the pilot action may need to be almost instinctive if control and structural integrity is to be maintained. I have always tried to avoid the advice of "lucky left / rotten right" for this reason. I am very confident that a very high percentage of us can remember which way the rotors were turning at startup (!) so the retreating blade is a very useful answer. *The lucky side is the retreating blade side , both for the safe side for the nose to be and the best side for the crosswind to be from on landing*.

P.S. *unless the pilot is faced with a very high TR power situation, which isn't too likely unless a servo runaway has occurred.

With regard to your question about C of G change.... a very significant change is very likely, to the point of the situation being non-recoverable.

[Bomber ARIS]

From the accident reports I have read, it would appear to be almost inevitable that one noses over and goes in inverted, at approximately 120 degrees nose down.

N.B. The above is not scientific; just a conclusion I have cobbled together over many years of reading the crash comics.

[SASless]

Bomber....

During a time and place far far away....a AH-1G Cobra took a hit from a SA-7 missle that removed the entire tail boom and related bits.....the crew (despite being at altitude) survived the incident. The aircraft remained right side up but spun like a top as I recall. One of the pilots is flying in the GOM today.....everytime I see him I touch his shoulder hoping some of his good fortune will rub off on me.

Some very good accounts are around about 412's that shed TRGB's.....some guys actually survived the events....though most do not.

[The Nr Fairy]

For the story of the Cobra / SA-7 mentioned above, see http://www.vhfcn.org/missle.html for full details.

SASless - can you get me a lock of his hair ?

[MightyGem]

How's this for TR jammed in low power, ie cruise. I've tried it in the simulator and it seems to work well.

Start to reduce speed, at some point the nose will start to yaw right(non French rotors). Set up an approach at this speed. The reduction in power for the descent will help. When happy with the approach, retard one engine to idle or shut it down. Maintain the speed all the way down. At the landing point flare off the speed. The reduction of power to more or less zero will stop the nose going right, it may indeed swing slighty left. As the speed decays to zero, start pulling in power to establish a hover, roll off the throttle on the remaining engine or get the second crew (or well briefed pax :eek: ) to retard the roof quadrant, and cushion the touchdown.

As I said, it works well in the sim and may be preferable to a double engine off landing.

[Ascend Charlie]

Back in 1981, the RAAF had a UH-1B which crashed. The T/R pitch change cables ran beside the drive shaft in the upper tunnel (in later models they were moved to the lower one). One cable came off the pulley and wrapped around the drive shaft, causing a full control deflection. The T/R blades flapped way past their limits and struck the fin, causing part of a T/R blade to depart the scene. This imbalanced the gearbox which tore itself out of the fin.

The resulting CG change pitched the nose down, and combined with the yaw, caused a mast bump. The main blade separated, but on its way out, it sliced through the left cockpit, bisected the copilot, removed the left door and then the tail boom. The remainder dropped / fluttered to earth, 3 fatalities.

No time to react.
:ugh:

[sycamore]

For anyone interested , `Gallery` p19 shows what can happen when a blade comes off; took the other blade and gearbox with it; just had enogh stick left to flare into/onto a small clearing on top of a hill.....