I had a quick look at Section 8, Training. It makes a big thing of the use of simulators, preferably with 6 DOF (Degrees Of Freedom). Fine for the military with the Lynx, but do CHC or Bristow have anything so elaborate? And coming down the pecking order, I have yet to come across an R-22 sim with any DOF at all.

Page 155 names several schools that describe TRF at least in passing, but - for a report released in November 2003 - I thought it strange that SouthernAir were mentioned. Didn't they go the way of all good things a little while ago? Like, two years?

But fantastic spot, Nr. You also beat me to it with the December bulletins.

What a tome! A most impressive body of work, with many things to learn and more to ponder. The discussion by Steve O'Collard at the end is worth the price of admission!

Some concerns I have:

The failure rate appears all out of whack to me. I see the rate of approximately 20 per million hours on the tables (notably P. 40) but that seems awefully high, based on the failures I know of for the aircraft I follow. For example, at 20 per million, I would have expected about 50 TR failures on S-76 fleet, but I can only recall maybe 5 if I stretch. For Black hawk, that would have to be about 80 tail rotor failures, again a big number.

Introducing a new and potentially eye-watering system like a parachute that always deploys when the tail rotor fails and never ever deploys otherwise is an interesting concept. It is kind of like the guy who carries a bomb aboard all airliners that he flys on, because, "The odds of there being two bombs aboard is so very low, I am completely safe!"

The study does survey lots of options, and does call for more and better design attention for TR systems, certainly important if those pesky data are accurate. And the call for monitoring for failures is positively 21st century, as the S-92 has about 20 vibration monitors for the drive train alone, all reporting through a Level A software system.

Thanks for the steer, Nr. Good stuff.

Ya , Thanks for posting the link NR.

Would two tail rotors be safer than one?
http://www.UniCopter.com/Temporary/TwinTailRotor.jpg

Would no tail rotor be safer than one?

:D :D :D

Tail Rotor failures
 

Summary:

The report contains what the CAA describes as the "deliverable" from from the QinetiQ research project ‘Helicopter Tail Rotor
Failures’ carried out for the CAA under a contract awarded to the Defence Evaluation and Research Agency (DERA) in 1997. The project was co-funded by the Ministry of Defence.

The project studied tail rotor failures and their consequences and was carried out because of overwhelming evidence gathered by the UK Tail Rotor Action Committee that TRFs were occurring at rates much greater than the airworthiness design standards require. This was true for both tail rotor drive and control systems, and applied to both civil and military types.

The principal aims of the study were to analyse and quantify the nature and extent of the problem, and explore ways to reduce failure/accident rates and/or mitigate their effects in the future. In addition, existing training procedures and handling advice
were examined and means of improvement suggested to prepare aircrew better for the effects of TRFs.

The study looked into the nature and extent of helicopter tail rotor failures, techniques/technologies to reduce occurrence and/or mitigate consequences, existing emergency procedures and handling advice, current pilot training practice and simulators, existing airworthiness requirements. It included piloted simulation-based experimental work.



(If you're not on broadband, it may be easier to download the file first.)

I've browsed through this weighty tome, and was impressed by the detailed work.
More specific comments will have to wait for a thorough review, but aside from generating more TLA (three letter acronyms) that will probably cause confusion, there is little to fault with the work done.
We do need to simplify things here so that we can help to train everyone
for example - for engine fuel control problems, the advice of 'high Rotor RPM, high engine bad (for multi-engine machines) and Low Rotoro RPM - low engine bad' helped to simplify a very complex subject.
Does anyone have any thoughts on this - like (for N. American direction of rotation main rotors) - yawing right, no sinking- loss of tail rotor, yawing left plus sinking= loss of engine (on the assumption that your tail rotor control system is unlikely to give you a hardover, but could perhaps jam)

Shawn,

For pilots who fly both American and European types (opposite main rotor rotations) and I am one, there is a big danger of confusion during the initial stages of a T/R malfunction, which can jeopardise the recovery. At a simulator for the S-76 I attended, there was constant reference to the terms "Lucky Left & Rotten Right", I'm sure you will have heard this used, too. I don't like this term because for a european helicopter it is "rotten left & lucky right".

I thought myself through this during my RAF time carrying out instruction on the Puma Sim. I came up with the following maxim:

The LUCKY side, no matter what the direction of blade rotation, is the RETREATING side!

Much easier to remember, as most pilots do actually remember which way the rotors went on start up!

Merged threads.

T/R failure in forward flight....
 

All you experts out there - If T/R failure occours in foward flight and enough forward speed and height is available to enter autorotation after chopping the throttle - should the aircraft be flared before making a fast run on landing or not? I am very interested to see what advice is given here by ye old lags. Thanks.

some-ones going to ask
 

the question some one will throw back, is, "what type of failure"

- loss of component (t/r departed)
- loss of t/r control (pedal inputs do nothing)
- fixed pitch failures (how much pedal at failure and which pedal)

type of failure dictates recovery, autorotation may not be necessary


:ooh: i guess that someone was me

As he's chopped the throttle I would think it's a drive failure. Can't recall anyone telling me not to flare. It would be useful to get rid of some excess speed. Of course there may well be yaw in the direction of the blade rotation, due to friction in the transmisssion.

I mean total T/R failure - component loss, broken gearbox, snapped drive shaft - aircraft still able to maintain main rotor thrust.

FS,
You still have some very differnent problems. Loss of component ie: GB or T/R departed , life becomes extreme very fast, due to cg change. You gonna spin , buck and it'll be a wild ride (more than likely) Do what ever you can to keep it flying , even in an auto. It aint gonna be pretty.

snapped driveshaft, or gb fails, use airspeed and or collective pitch adjustments to keep it flying if possible, to a spott where you can auto to or run it on without a scratch if your lucky. Lot of this depends on AC , gross wieght, other enviromental factors, etc.

Every one will be differnt....
like some of these salty old guys around here say. Thousands of hours of sheer boredom, moments of stark terror.

RB

lets say an auto is required --

i've been told (no personal experience), and it makes sense to me, that a flare just before touchdown, besides loosing forward speed, and held (mild flare, not standing it on it's end) so that the stinger makes contact with the ground will have the efect of straightening out the airframe before the skids touch.

having the heels of the skids touching first will also help keep you aligned

wouldn't want to touchdown full skid with a 45 deg nose angle:ouch:

If it's a Squirrel and a simple drive failure, then you should be able to maintain control, fly to a suitable field and carry out a powered run on landing. As one of my colleagues did a few years ago.

There is no straightforward answer. The main variables are aircraft type and landing area condition. If the only place to touch down is full of obstacles (the pilot might have little choice) obviously one needs to reduce forward speed by flaring as much as possible. Shame to survive the impact but at high groundspeed and subsequently watch a stone gatepost get closer to the "between the legs" position.... :\

Some aircraft are best engines shutdown (most I have flown are), some are OK at engine ground idle, and some may be better placed with regard to a speed / power combination. Reading the Flight Manual is always good advice and simulator training helps too.

At night I would want to reduce g/s as much as possible, even at the expense of a higher rate of descent.

Try this though it's hardly light reading CAA study The one line version being:- know the right technique for your aircraft.

407 Too,
Better to level the machine before putting it on the ground. Landing heels first with the disk tilted back runs a good chance of chopping of the tail boom.

Flying Squirrel,

In answer to your question -which, if I'm not mistaken is - "If I've entered autorotation after a T/R failure should I flare at the bottom?"

Yes under most circumstances. If you have rolled the throttle off to achieve aircraft control after T/R failure and the area where you are about to land is not a runway then flare. In a crash forward speed kills so reducing the forward speed to zero just prior to touch down will significantly improve your chances of survival. Directional control should not be too much of a problem through the flare if you have a fin. Expect some yaw in the direction of rotation as you intial the collective. This is due to you imparting a decelerative force on the blades when you initial. The torque reaction of the fuselage is to turn in the direction of blade rotation. The attitude now must be levelled prior to cushioning at touch down. During the touch down you will be rotating but much less wildly than if the throttle was open. Fly to touch down in a level attitude. Hopefully the aircraft will remain upright but even if it doesn't the lack of forward speed will hopefully ensure minimal injuries.

However, depending on the aircraft type an autorotation is not always the immediate solution to a T/R malfunction. The manufacturer's recommended solution is probably most appropriate.

In the case of a loss of T/R Drive or loss of control linkage it is probably advisable to fly the aircraft to a runway. Enter autorotation by lowering collective and only roll the throttle off after achieving a slow enough run on speed and lined up with the runway.

In the case of catastrophic failure and loss of components, the longitudinal CofG problem is now going to dictate whether the aircraft can be controlled and therefore whether the throttle should be rolled off straight away.

There's not enough room here to go through what to do for a jammed pedal.

Note these are general solutions and may vary from type to type and configuration to configuration. ie wheels vs skids, PCL vs twist grip etc

Your best bet is to sit down for a long chat with a crusty old instructor and satisfy yourself you can identify the type of T/R emergency and the best way to deal with it.

PS The suggestion that friction in the transmission is the cause of rotation after initial at the bottom of an autorotation is a myth. It belongs in Mr Lappos' thread about urban myths. The rotation is due to the decelerative force on the blades at initial.

"However, depending on the aircraft type an autorotation is not always the immediate solution to a T/R malfunction. The manufacturer's recommended solution is probably most appropriate.

In the case of a loss of T/R Drive or loss of control linkage it is probably advisable to fly the aircraft to a runway. Enter autorotation by lowering collective and only roll the throttle off after achieving a slow enough run on speed and lined up with the runway."

First paragraph of that advice = :ok:
I agree with you there, but the second paragraph = :(

I have to strongly disagree with the second paragraph. It is VITAL to know your aircraft type because on some aircraft, after a loss of tail rotor drive, any attempt to "fly to a runway" other than in autorotation may result in loss of control. This technique may be a good one if the tail rotor is still producing thrust, i.e. control of the pitch angle has been lost.

We must be very careful with this subject. Trying to give general advice on how to handle a tailrotor malfunction may be inappropriate.

ShyTorque,

I see your point, no fin could equal disaster without the throttle off. I can only reiterate that a long discussion with an instructor about the type/s flown is the way to go. There is no simple "one size fits all" answer. Please see signature below.

Cheers.

To add my two-penneth regarding run-on speed and ROD; 1500fpm is about 15kts downward, 500fpm is about 5kts, 200fpm is about 2kts etc etc. Therefore, after the helicopter has broken its contract with you in such a major way, a relatively high RoD at touchdown is probably preferable to a high-speed run-on as the overall overall inertia, and therefore bone-breaking forces, will be less.

What about flaring to zero-speed? Not a recommendation; but a genuine question?

J

jellycopter,

If I had to do an autorotation to maintain control and/or a powered run on landing was not possible, that's exactly what I would do, flare to zero touchdown speed.

It will yaw late in the flare, as you commence the collective application, but who cares? I would rather contact the ground with no speed and turning than roll it over at speed. The key is to make sure the power is off, lose all the speed completely and get it level prior to touchdown.

TheFlyingSquirrel,

As to your original question, what were you trained to do?

Silberfuchs: tell us what happened to you 10 yrs ago?

I believe that one solution, as there are many ways to skin a cat, is to fly to an area where you will be happy to autorotate into, preferably an airfield as there is a runway and crash facilitys, otherwise best choice available. Let someone know, MAYDAY, dont delay to long there could be a lot of metal thrashing about back there and it could get worse shortly.
Enter Autotrotation close the throttle carry out Immediate Actions make sure the fire making stuff is shut off. As you approach the height specified in the a/c manual flare the a/c reducing speed to zero if possible and aim to come down the last 10 feet verticaly using the collective to cushion the impact. You will spin due to friction but that should be manageable, if you come down verticaly you will hopefully reduce the possibility of rollover associated with high speed run ons.
This may not be the perfect solution but it is the plan i have worked out for myself to give me something to work on come the day.
All comments welcome:ok:

Have a look in the POH. My Enstom POH details what to do for every concievable type of TR failure. The details may not be relevant to other types as Enstrom make a big issue of the fat tail boom helping get you out of trouble.

A good start point for fixed-pitch type failures was taught in the RAAF for a long time, works well for helicopters with twist grip throttles like the B205, 206, and we had twist-grip mod squirrels.

In a nutshell, set up on a long low final for a good run-on area and slow the aircraft in 10 kt increments, stabilising level and unaccelerated to see what the yaw angle's doing.

If yawed left (rotor anticlockwise from above helicopters), keep slowing down in increments until you get 40 to 50 deg. left yaw. or 20 kt. Maintain the speed you're at until over the landing area, then smoothly slow to the hover. If it turns left, reduce your Nr in small increments with beep or throttle (yaw will initially speed up, then slow as the tail rotor slows down and you pull a bit of pitch to stay in the hover).
When the yaw's stopped, put it smoothly on the ground.

If yawed right, slow to a minimum of 20 kt or maximum 20 deg right yaw. Maintain that speed until over the run-on area, then take a 'bite' of throttle to swing the nose straight and conduct a fastish taxiing auto. Use any further throttle to 'steer' (the nose will go in the direction that the bottom of the throttle goes).

In the yawing left in the hover case above, if it starts to go right, again take a bite of throttle and do a hovering auto.

This set of techniques works really well, and has the advantage of being a bit 'scientific' and repeatable, ie gives you some procedures and limits to hang your hat on.

For more catastrophic things like loss of tail rotor components etc, I'm all for setting up for a zero-speed auto as some people above are advocating.

There are a few helicopters that, depending on the components lost and gross weight may achieve sufficient streamlining to continue powered flight to a more suitable landing area. Others can't be streamlined sufficiently no matter what the weight, and will spin until the torque is removed.

Still others fall somewhere in the middle and the outcome depends on airspeed and other factors.

In any case, while it may be possible to run the aircraft on, the better choice seems to me to be zero-airspeed autorotation, which greatly reduces the kinetic energy that needs to be dissipated at touchdown.

-Stan-

You guys may find this interesting reading, its a CAA paper on tail rotor failures, and the procedures highlighted in a number of flight manuals. A bit long, but interesting if you like that kind of thing.

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

Cheers

V.

I was a pax on board an Alouette III recently and experienced loss of tail rotor command first hand. The solution to getting us to the ground safely seemed to be a combination of a few of the last posts.

Immediately the problem occured (just after take off from a clearing amongst some cocnut palms) the pilot elected to head back towards the nearest airfield (a virtually unmanned third world scrape in the jungle), a journey which took an agonising 40 minutes.

His approach was long and low, progressively easing off the speed as we got closer to the field, allowing him time to assess the degree of control. We had the benefit of about a 20kt head wind which meant that he was then able to bring us almost into the hover.

So as the yaw started to kick in and the outside world started to rotate he executed what one might term a "positive" landing. The Alouette was equipped with wheels but the pilot chose to land in the long grass off the runway which seemed to help in absorbing the impact of our landing. The outcome however was that we all emerged unscathed (and the a/c was easily repairable).

Hats off to our pilot, he handled it extremely calmly and I really hope that I get the chance to fly with him again. Unfortunately we had to abandon the heli and switch to fixed wing to complete our task. And the cause..., a failure of the t/r command cable.

It was a clean break of the control cable just forward of the helix drum around which it wraps in the tail rotor assembly.

Please bear in mind that I am not qualified in the engineering department however as far as I could see there seemed to be no signs of wear and tear, and the operator informed me that it was only six months old. The break was so clean that it looked like it had been cut.

I have a picture of it if you're interested.

McHover

I’m grateful to this thread for sending me back to the notes I made the day after suffering a complete T/R drive shaft shear in a 109 some years back. (I caution when reading this that the 109 of course has a very big fin). Part of those notes read:……..

According to both the previous tail rotor failures on 109s the aircraft doesn’t yaw with a failure in forward flight above 120 kts since the tail rotor is completely unloaded and the fin is taking the entire anti-torque load. However in both these cases the entire tail rotor assembly had departed the aircraft. Mine was attached and sometimes windmilling, sometimes not. (I had a chase S76 join me to take a look).

There was a definite and violent yaw to starboard and there was no way it was ever going to fly in the direction it was pointing, or even within 40 degrees of the heading. Although that was uncomfortable it would happily fly at a good range of power settings and between 60 – 100 kts, leaning heavily left “wing” low. The envelope is undoubtedly much wider but I wasn’t brave enough to explore it!

I flew dummy approaches to two out of wind runways in the hope of gaining some help with the heading but the whole thing felt very unnatural and there was no conspicuous advantage to be gained.

I trained the camera man in the left seat (we were returning from a job together) to chop the overhead throttles on my shout. The into wind runway was chosen and I entered a 60 kt constant attitude auto with the engines running (and without intending to flare). The nose stayed 20 degrees to the right of the centreline. At about 20 feet we chopped the engines. It felt very late at the time but was actually a bit early as I was amazed how quickly the nose yawed to port whilst I was pulling in a bit of pitch. I was hard pressed to get onto the ground before the nose swung through the centreline.

In retrospect I would not do an auto next time. I think I would go for a flat approach at 60 kts and accept the increased yaw to starboard (probably as much as 45 degrees). I would then try to gently arrest the descent and then the speed down the centreline at about 5 –10 feet before chopping the throttles, giving more time to worry solely about timing the touchdown to coincide with runway heading. This assumes somebody available in the other seat to look after the throttles.

I found one of the hardest aspects was keeping my feet on the floor instead of constantly trying to pedal a control that wasn’t there.

…………Now don’t ask me for more details, it was a long time ago, but those notes were made the very next day. I’m certain they are very specific to the 109.

I do very clearly remember being astonished at how the brain speeded up with adrenalin and could remember comprehensive details of stuff I’d read or been told about T/R failures from long before. I couldn’t have remembered it all the day before and probably not the day after, but it was all in there somewhere when needed at the critical moment.

JerryG

McHover's failed cable....
 

http://img.photobucket.com/albums/v6...mandcable1.jpg

http://img.photobucket.com/albums/v6...mandcable2.jpg

T/R failure in forward flight
 

Interesting notes, pitch controil fails or drive shaft fails. simple, play with your throttle, wind it off just before you touch down at very slow forward speed. don't stuff up the aproach.

If drive shaft fails in the hover, man that's scary, after the second rotation one's self preservation usually remembers training, wind the throttle off idiot, they don't stop, only slow down a bit.

What not to do is don't wind it off, check out the story from Sydney Australia many moons ago when this happened in a tele-news 47 after the old leightweight style T/R thru bolt let go, very messy and all on camera.

If the G/Box is gonna fall off, do your CofG, then work out how you might kiss your posteria goodbye!

But refer to the recent seaking crash on the after deck of travelling ship, many cowboys reckon that T/R fails, no-one noticed the rapid quick flex down and up of the M/R when it unloaded in a typical vortex ring state, of course the T/R parted company with the rear end of flight path when it also got fouled up air.
Maybe no one has ever seen a cowboy film when the wagon wheel goes into slow flicker motion when in synch with and at right angles to the camera?? T/R was still going ok when it went past the cam close up and also when it smashed with high power into the deck and disappeared to the port side of the vessel.

A technique that works in the Huey Simulator (or AB205 etc) following a loss of drive to the tail rotor:

1. Enter auto and roll throttle off to reduce tendency to spin to a minimum
2. Establish fairly fast auto to get some benefit from the fin
3. During auto gently re apply throttle
4. during the flare as the speed reduces and you start to pitch pull, the aircraft will begin to yaw due to frictional torque produced - at that stage start rolling off the throttle and that will help to keep straight.

Don't know if this is a "works for all" technique but it works on the Huey so my guess is it might work on 206 and other Bells.

Any one have use of a 206 sim to give it a go? Please let us know the results.

While a very new US Army pilot...in a land far-a-way....bummed a ride to H-3 Heliport in Saigon...sat in the front seat. Normal flight to H-3 with one stop in Di An for fuel....then to H-3. Arrived at H-3 to the hover....brief discussion about where to park...still at a hover....I point left ...the pilot looked left...and the aircraft turned right. Me being quick witted assumed the guy was doing a clearing turn or something. As the nose passed what had been the original 12 o'clock position we continued to turn right but at an ever increasing rate or rotation. The first turn felt almost normal in rate but did speed up as it progressed. As the nose passed the 12 o'clock position for the second time....and the rate of rotation was becoming interesting....being really quick witted...I asked the pilot what he was doing. As the nose passed the 12 o'clock position for the third time in a blurring eyeballs against my Aviator Ray-Bans.....again being quick witted I ascertained the pedals were full left, the world was still spinning left, and that my now deaf and dumb pilot.....was not reacting in as correct a fashion as I desired.

I asked him politely, in my slow measured southern drawl, to reduce throttle.....sounded kinda like an excited Geordie SgtMajor calling drill commands....."Chopthethrottleforchrissakesyouidiotwhatareyou tryingtodokilluschopthethrottlechopthethrottlepleasechopthet hrottleplease!

In desparation, fearing this guy was going to be like my Commanding Officer trying to decide what kind of marks to give me on my annual evaluation, and that I had other more pressing business to attend to.....I politely without saying anything to him...snapped the throttle off from my side. Not that I was aggressive with it...but the leather covering on the throttle came off in my hand as I recall with weird clarity.....and the rotation immediately slowed to an almost sedate pace....the world was only partially blurred. We landed with a good thump, sounds of paperwork being generated, and the aircraft took a decided list to port and settled by the stern. I opened my door, stepped up to the ground and tipped my hat to the pilot and headed for Saigon to visit the Christian Serviceman's Reading Center for a Kool Aid and cookies.

It is amazing how quickly the rotation slows or stops with the reduction of torque in a loss of thrust situation.

Anyone notice that the 'big guns' haven't pitched in so far? Probably it's because there is no single answer to this. React today in a certain way and you might get away with it - do exactly the same thing in the same machine tomorrow and we might all die (different weight, alt, temp, TAS, etc). Try it in a different machine (whichever way the blades go) and everone is toast every time. Trust the simulator if you're brave enough, but remember the way it responds is just a guess.
ANSWER (assuming control failure):
1. Don't panic.
2. Fly what you have left.
3. Don't panic.
4. Consider the wind direction for landing (having already thought about this on the ground one foggy day in advance!)
5. Don't panic.
6. Do everything slowly.
7. Don't panic.
8. Don't hit anything while not panicking!
9. Don't panic.
10. Good luck!

I did one in a Robbo once as a demonstration for a student. I set the pedals to a pre determined position that gave neutral TR pitch (almost full right pedal). Rolled off the throttle and entered auto. At the bottom at the end of the flare it started to yaw left quite slowly and then more as the collective pitch pull came in. We touched down about 90 deg left of the original heading, so the key is to make sure you lose all ground speed. Either that or run it on at about max touchdown speed of 35 KT before it starts to yaw.

CareBear,

As per your scenario, I have used a very similar technique in the B206. Once established in the auto at speed, roll the throttle back on. Use only enough collective in the descent to prevent an Nr overspeed. During the flare and pitch pull, as it starts to yaw under torque, roll off the throttle to keep it straight and touchdown. Very controllable.

I think a genuine drive failure would be noticeably different to a simulated one though, due to the tail rotor still providing some stability even if it didn't have any pitch applied.

I guess the original question "in forward flight" has morphed into a general TR failure discussion. Whenever possible, practice, practice, and if you can, practice. Two I've had were both my fault, and instinctive reaction got us out in one (relative) piece on both occassions.

Low level filming in a 206L, I got distracted and hooked a wire under the toe of the left skid. The Mayday was instinctive, the decision to pull power to break the wire was the only solution (we were hanging nose down in our straps by then, with full aft cyclic), and I have no recollection of rolling off the throttle when the wire broke and I cut the tail off with the rotors. But it must have been instinctive, because we didn't spin :cool:

We were lucky enough to come down upright, but I snapped the collective trying for that last degree of blade pitch, and the back does still hurt now and then :rolleyes:

http://www.helicopterservice.com.au/...rike%2010a.jpg

http://www.helicopterservice.com.au/...rike%2011a.jpg

The other was in the BK117, at night, backed into a tree in a high hover. The decision to dump the collective was done without thinking, and got us out with a slightly spread set of crosstubes, rather than rolled up in a ball.

No obvious training is going to account for every eventuality, but lots of practise (or mental preparation) will go a long way to making the right move "in extremis", the correct move :ok:

ppng said, "Anyone notice that the 'big guns' haven't pitched in so far? Probably it's because there is no single answer to this. "

Right on!

The idea of a "failure" consumes paragraphs describing what tail rotor thrust is left - lots, too much, cruise power, almost none. full right?

Then we deal with individual models of helo, and then with varying flight conditions, and then with experience levels, whew!

I'd rather answer, "Honey, do I look fat in these slacks?"

Boiled down to a short, accurate helpful answer, I like ppng's checklist just fine!