Thanks to ALL for the excellent posts.

Cheers, OffshoreIgor http://www.pprune.org/ubb/NonCGI/eek.gif

Landing w/o tail rotor!?!?
 

A question to you rotorheads:
We had an Apache lose it's tail rotor a few weeks back, which then went on to land safely by maintaining a high speed so the tail would act as a stabilizer.

Anyone care to explain this in a bit more depth?

Cheers
DT

DT,
can you explain in more detail what you mean by "lost" tail rotor. Did he/she lose the tail rotor gear box and blades, lose tail rotor control, or lose tail rotor drive.
The exact emergency procedure is different for all of them.
However, the vertical stablizer has a function to act as a air foil and produce thrust to help maintain streamlining of the fuselage. This unloads loads the tail rotor, the horse power that would have been used to drive the tailrotor is now avialable for the main rotor to use for lift and thrust. The streamlining is most efficent at some airspeed, probably in the neighborhood of 60kts, that the designers have determined. The streamlining should allow the helicopter to be landed with out tail rotor contol, or drive with a smaller pucker factor margin. The exact procedure is individual to the type of heliocpter, so this is a generic statement of the function of the vert stab in tail rotor failures.

Loss of tail rotor is a big problem in any helicopter, especially since the vertical fin (which now must provide all your anti-torque) is often reduced in size to reduce blockage of the tail rotor to help increase tail thrust for better crosswind control.

The previous post that discusses the different problems depending on how much hardware is shed is correct, but only in the additional problems that a CG shift bring about, where the tail is immediately a lot lighter at the same time that the tail rotor thrust is entirely gone. For the rest of this discussion, let's assume that the tail rotor thrust is now zero, and no other problem is compounding.

The vertical fin can help in recovery from a loss of tail rotor thrust by providing some right thrust, but it will do almost no good until speeds of about 1.5 Vy, typically about 110 knots in a high speed helo (S-76, Black Hawk), maybe 80 knots is a slow Bell type machine, and maybe 60 knots in a light piston.

This is because the fin area is usually small, and it takes some forward speed for it to generate enough lift (side force) to be much help.

If you try to fly home at higher speed, the increased power you need means that you also need more anti-torque, so you might not make a powered flight situation work.

How do you know? I suggest that if you experience loss of tail thrust in cruise flight, (sharp right yaw in an American helo, left yaw in a French or Russian machine -- I will use the American convention below) get control of the yaw situation first. Lower the collective immediately enough to stop all yaw and allow a steady state descent. Carefully guard your airspeed, try to stay at a high speed autorotative glide speed (about 1.5 Vy in most helos). If all is going poorly, go to full auto and take your chances on the landing. If the glide looks good and yaw is well behaved, you MIGHT try to gently increase power to reduce the rate of descent, while maintaining speed. The aircraft will start to yaw right as power is applied, so you must cross control by applying left bank to keep the heading stabilized. You will probably have to go more nose down because you have much more drag, and you must watch for two big danger signs - excessive yaw like a flat spin, and loss of airspeed indications, where the pitot probe might give up working in the big sideslip. At the first sign of either danger sign, lower the collective pitch and the nose to get the torque down and the speed up.

For most helos, you will not be able to get to level flight because to torque you need will produce an excessive sideslip or even a flat spin (the ultimate problem in all this test pilot heroic stuff). Settle for a reduced rate of descent, since it really helps you extend your choice of landing areas. If you can get to as little as 750 feet per minute descent, and you are doing 100 knots, you can travel 3 miles from 1500 feet, almost 7 miles from 3000.

At the bottom, transition to a reduced collective flare, and make a part auto-part running landing. Don't increase the collective at touchdown unless you have decoupled the engines, as the sudden torque rise will create a big spin, and a real crack-up.

The skills needed to fly out of an anti-torque failure are not trivial, and most pilots are best served by thinking and performing an autorotation, period.

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Nick, I'd like to ask you a rather odd question, given your test pilot background. Would a small drogue chute help with a loss of tail rotor problem?

My thinking is that the drogue could be released from the extreme end of the tail boom (below the tail rotor), and the chute would also need a jetison mechanism. I was wondering if you've ever heard of such an idea.

My thinking is that following the loss of tail rotor thrust, and once the yaw has been stabilized and a descent rate with good forward airspeed established, then the drogue could be released. It seems to me this could help to add additional stability to the yaw so more power and collective could be re-applied. Of course good forward airspeed would have to be maintained for the chute to remain affective in contolling the yaw.

If the chute were effective enough at controlling the yaw so that a small climb rate could be established, then you'd have your choice of landing areas. A run on landing might be easier to accomplish with the chute, and at the very least perhaps you could choose the spot to perform an autorotative landing, which is much safer to perform if you can be selective about the landing area.

Does this idea make any sense?

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Safe flying to you...

[This message has been edited by Flight Safety (edited 01 July 2001).]

I have had two T/R malfunctions. The last one was in an A-Star while on final to an offshore platform. Prior training had taught me how to land after experiencing a T/R malfunction, but not how to get out of the spin. I increased the collective, which initially increased the spin, but I had to avoid the crane on the platform. Started feeding in forward cyclic and eventually got it under control. Not easy on any day, but a little more trying with two passengers screaming like girls. Flew back to the beach with a slight slideslip. Above 40 kts. the aircraft will streamline. This goes for a 206 also. Did a running landing in the grass. Slowed down to 40 kts. on final and slowed it up some more. This initially increases the yaw rate. At the bottom, pulled on power, the nose aligned, and ran it own. I wouldn't do an auto unless you have loss of components. Why give yourself another emergency to deal with.

GulfPLt, you're experience reminds me of an idea I've often had regarding loss of T/R.

I saw a video about a year ago of an ANG Blackhawk performing a rescue of an injured climber in a small but deep rocky ravine (if I remember this correctly). The ravine was too small to land the helo in, and the rocky sides were so narrow they would have caused rotor contact if a landing were attempted. Surrounding this small ravine on 3 sides was fairly flat terrain.

In the video, the Blackhawk had just gotten into position to lower the winch cable, when suddenly it lost tail rotor thrust. The Blackhawk began to spin, and for some reason that was not clear to me, it went straight down into the ravine in a slow flat spin, destoying the main rotor in the process as it contacted the rocky walls. The airframe landed right side up at the bottom and all the crew survived (some with injuries), and another Blackhawk had to arrive on the scene to winch all persons out of the ravine.

What puzzled me was why the pilot didn't apply more collective and climb, so he could straighten it out with a little altitude and attempt a landing on the surrounding flat terrain. I know this would have increased the spin rate, but as long as the airframe structure can tolerate the increased spin, this would have been far better than destroying the helo in the rocky ravine.

So that's my idea, why can't pilots do what "GulfPLt" did, and just climb if needed while enduring a higher spin rate, if that's what it takes to get out of trouble following the loss of T/R, especially at low altitude above an uninviting landing area?

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Safe flying to you...

Regarding the T /R loss. Two cases are to take into account: loss of the T/R itself or loss of the control ( linkage between pedals and rotor).

The first case is worst because, there is no more thrust anymore and the stability of the fuselage is ensured only by the fin, if the helicopter is equipped with such device. In such a case, if the failure occurs in hover, there is no chance to recover the helicopter as the torque, at the occurrence is too high. If the failure occurs in flight, the helo is flyable but the only solution to rejoin the ground is autorotation.

In case of loss of control, the case is less dramatic as there is a remaining thrust. I remind my instructors teaching me the high side loss or low side loss, with specifics procedures according to the case. Modern helicopters have sometimes a damper located on the T/R system which set the T/R blade pitch angle at a standard angle in order to provides a permanent thrust. In such a case, running landing can be attempted with good chances of success.

Take a Dauphin. With its huge fin, loss of T/R control in flight could be unnoticced. It is possible, but not advised, to land such helo in hover while experiencing a T/R loss of control if the helo is light and there is a 15+ knots of wind set exactly on the RH side of the helo during a low flat approcah to land.

Cheers

Ancient Pelican-he lost the rotor completely, it detached itself from the tail.
The crew got a reading saying it was stuck, but saw it fall/spin away.


you all keep saying that you can still fly the helo. At high speeds I can understand this, but how can you keep it straight during landing?
The only landing I can see is a running one-yes?

Thanx for the replies-very interesting.
DT

I think you will get a dozen different answers to the same question with this one, depending on individual's experience.

Touch wood, I have not experienced a tail rotor problem though I have spoken to several pilots who have and I also include stuck pedals occasionally on Proficiency checks.

What is evident, with a stuck pedal, is that the transition from seemingly controlled flight to loss of control can be very rapid and with little warning. In the event, disciplining your actions against your instincts can be dificult.

The yaw rate that could develop with total loss of thrust must be huge and extremely disorientating. I suspect that if you were to exacerbate it by pulling collective to climb, you could get yourself really 'lost in space' and the rate of yaw may not beacome recoverable despite any actions. Throw in loss of componants and the ensuing C of G shift and things get really interesting. I could imagine that with a teetering head there would be a real risk of blade strike to trying to dive on speed while rotating like a Derbisher.

I know, personally, 4 pilots who have experienced loss of tail rotor componants and thrust in 4 different Puma and Super Pumas. In every case they were in the cruise or a shallow descent, with good speed. In every case they rotated rapidly about three axes and in two case crashed/ditched out of control. The other two were recovered to autorotation only after closing the speed select levers (collective insufficient on its own) and successful ditchings followed.

I also read an article in the Navy's flight safety magazine, written by the crew of the EH101 that crashed following a tail rotor control failure at 10,000. The 4 crew bailed out after all attempts to regain control were lost. The description of the rotational g forces and attendant escape problems was particularly interesting!

So, basically, I think it would be true to say that a tail roror failure may not be the end of the world and there are many cases of successful recoveries from such problems (eg Gulfplt). However, I think it is niaive to think that it is a straight forward problem that can be recovered from using a standard technique. Glib remarks like "I don't understand why they didn't JUST pull power and gain height" seem to show a lack of understanding of the nature and seriousness of the problem.

BTW, I don't know if you are at the FSI Bell facility,FSI, but if so I do think the simulation of tail rotor problem in the 212/412 sim is a touch optimistic. You come away (or could do) thinking it would be no problem at all.

Like the idea of the drogue shoot, FW have used them for years for spin testing.

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Another day in paradise

See these recent threads which have appeared on Rotorheads :

Tail Rotor Problems

Tailrotor Fun $#@! - Harry, did you get any responses and have you had a chance to collate them ?

As I've never had a t/r failure for real, I don't suppose there's someone out there who has access to the right people and the right toys to play with this sort of stuff in the sim, is there ? Perhaps a bottle of whisky for the best answer ? :)

[This message has been edited by The Nr Fairy (edited 01 July 2001).]

Nick Lappos
Thanks for the post. Hope to read more contributions from you from time to time.

http://www2.gdi.net/~nlappos/jobsite.jpg

Nick Lappos is Sikorsky's Assistant Chief Test Pilot. A former U.S. Army Warrant Officer and a combat veteran of Vietnam, he flew Cobra attack helicopters in D Troop, 1st Squadron, 1st Cavalry. An Aerospace Engineering graduate of Georgia Tech, he came to Sikorsky Aircraft in 1973. Since then, he has flown in the YUH-60 Black Hawk program, flown the first flight and structural shakedown of the S-76, the "Shadow" cockpit research aircraft, the adaptive fuel control experimental aircraft, and the "Fantail" fan-in-fin demonstrator. He is now assigned to the RAH-66 Comanche project, where he is part of the pilot team flying the shakedown and envelope expansion.

In 1988, the Society of Experimental Test Pilots awarded Nick their Tenhoff Award for the most outstanding paper at the Annual Symposium. The American Helicopter Society awarded Nick their Feinberg award as most outstanding pilot for his contribution to the understanding of maneuverability in 1989 and again in 1998 (as part of the Comanche Team), and in 1994 he was named a Fellow of the Society. He was a member of the American Helicopter Society's Handling Qualities committee and AGARD Working Group #19 (Functional Agility), and is currently a member of the NASA/FAA Air Traffic Management R&D Executive Steering Committee.

Nick has written a number of technical papers, and articles for magazines such as "Rotor and Wing," "Interavia," and "Defense Helicopter." He holds 15 U.S. and a number of foreign patents on flight and engine controls and cockpit displays.

http://www2.gdi.net/~nlappos/gearup2.jpg Photo of Apache during initial flight tests.

this is a video clip of a t/r failure at hover. Its pretty sobering.

http://www.helis.com/movies/taiwan.rm

Ties in with what I was trying to say. "why didn't they just pull pitch and fly away?" Yeah, right!

In fact the initial problem wasn't a tail rotor one. The a/c had a P2 leak due to a maintenance error, when it tried to come to the hover the power loss meant it started to sink and the Nr drooped. The pilot tried to arrest the descent by pulling more collective and they settled on to the water, at which point the tail rotor drive shaft failed as the fenestron started sucking water rather than air. The newly released power to the main transmission was sufficient for the a/c to get airborne again, with the pilot still pulling, at which point the a/c started rotating freely. Sadly, one of the pilots drowned.

Now you can see why check lists for a failure in the hover often say; "lower the collective immediately and accept the yaw". If you don't, it's going to get a lot worse very quickly.

PS The Taiwan 365 info came directly from Eurocopter in response to a question about fenestron power consumption in the hover (I'm writing from Marignane)

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Another day in paradise

Hm that Apache looks at lot like a commanche. I guess is hard for us paleface to tell them injuns apart though. Nice pics.

212man, where did I EVER suggest a modification to SOPs, WHERE?

My ideas run along the line that I'm convinced that more can be done in helo design to make loss of T/R more survivable (both for pilots and airframes). Obviously this puts the ideas in the realm of experimental flight test, where they belong. Clearly ANY new procedure has to be thoroughly understood through analysis and flight test before incorporating them into ANY SOP or emergency procedure. You're not foolish enough to violate this fundamental wisdom of flight, and neither am I. Enough said.

Anyway, FWIW, I was already having second thoughts about the drogue chute idea, as I see 2 problems already. One, a tether of any length could allow the chute to get caught in either the tail rotor or the main rotor with bad results following. Second, in forward flight with any airspeed, the chute could get caught in the rotor downwash causing an interesting pitch problem.

A third idea is that it might be helpful to design the tailboom as a structure that's both fairly narrow with broader flatter sides. This might help in 2 areas. One, it could add more keel area to the rear of the airframe, thus augmenting the vertical stabilizer in yaw control in forward flight after T/R loss occures. Second, if you added collective to climb out of a bad situation, the broad flat sides could help control the spin rate by offering significant drag in the spin (all to be tested and validated in fligh test of course). The tailboom and remaining airframe structure would have to be stressed for the spin rate produced by a slow climb after loss of T/R, if such a capability were to be designed into an airframe.

The main subject of this thread was landing after a loss of T/R. I think its fair to discuss both ways to accomplish this with current SOPs, and what could possibly be done in the future to improve this particular situation in helo airframes.

All I know is that climbing out with increased spin rate after T/R loss is a reasonable idea with some merit in certain circumstances, as it surely kept GulfPLt from getting tangled up with a crane. His passengers may have been screaming like girls, but at least they were able to safely clean out their drawers after he landed.

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Safe flying to you...

[This message has been edited by Flight Safety (edited 02 July 2001).]

Army grounds Apache fleet for safety checks

WASHINGTON (Reuters) - The U.S. Army has grounded its entire fleet of Apache attack helicopters to inspect the tail rotors on the aircraft, an Army spokesman said Thursday.

The inspection was ordered as a precautionary measure following a June 11 incident involving a faulty tail rotor on an Israel Apache, spokesman Thomas Collins said.

"This action is a precautionary result of an Israeli AH-64A aircraft incident where the tail rotor head assembly separated from the aircraft in flight,'' Collins said.

Collins said each inspection would take about 30 minutes and would determine whether the tail rotor needed to be replaced. He could not say when the inspections began or how long they would take to complete.

"We're trying to accomplish the inspection as quickly as possible, but we also have to be as thorough as possible because the safety of our soldiers is of paramount importance,'' he said.

Collins said the tail rotor on the Israeli helicopter came apart during a routine flight. The aircraft landed safely at an Israeli air base, he said, adding that an investigation was under way to determine the cause of that incident.

The AH-64 Apache attack helicopters, built by Boeing Co (BA.N), have been grounded twice before, both times to check potentially dangerous tail rotor problems. The tail rotor controls the aircraft's ability to turn left or right.

The fleet was grounded in December 2000 after the discovery of a faulty tail rotor "swashplate'' assembly and in November 1999 after the Army found suspect rotor bearings and transmission problems following crashes.

Six Army Apaches crashed in 1999. Army officials said investigators found that a heating process used by Boeing to make the bearing assembly extra hard led to stress corrosion fractures in the bearings. ^ REUTERS

I wanted to try and summarize these weird ideas on loss of T/R I've posted, and relate them to what I think is the current state of dealing with the loss of T/R in the helo industry. My opinion is that dealing with the loss of T/R thrust is not nearly as well developed as it can be, and this poses some safety problems.

In the Penny Farthing helo configuration, we all know that the loss of T/R thrust is a significant failure that no pilot wants to face, but all pilots should be prepared for. For this discussion I'll focus mainly on total loss of T/R thrust and exclude jammed pedals, stuck cables, etc, and those failures with CG changes.

There are 3 basic methods of responding to this failure, which deals with the loss of the anti-torque required for directional control of a Penny Farthing helo.

Method 1 Reduce the Main Rotor torque to zero. This is the "reduce the collective, chop the throttle and autorotate to a landing" method. It is the method of choice for failure in the hover, and for inexperienced pilots. This is taught by all flight instructors to new pilots, and all new pilots learn autorotative techniques in training.

Pros: Stops the airframe from experiencing severe yawing. Relies on the autorotative ablility of the airframe for a "safe" landing. All pilots have a degree of training in autorotation. Most simple recovery technique.

Cons:Technique varies by airframe type. Not all airframes are created equal in autorotative landing ability. The choice of landing area is severely restricted.

Method 2 Low to mid range Main Rotor torque method. This is the run-on landing method where forward flight with a controlled descent rate at sufficient airspeed provides enough anti-torque for directional control, to allow a run-on landing in either grass or on concrete.

There seems to be a lot a gray area in this method. Not all airframes are well suited to this method. Not all pilots are trained in this method. This method also generally requires a lot of skill from the pilot (Nick Lappos spoke eloquently on this in his earlier post). This method is generally not well developed (with certain exceptions), in either airframe capability or in pilot training.

Pros: The pilot has much greater choice of landing areas. The airframe usually suffers far less damage upon landing.

Cons: Requires a lot of pilot skill to accomplish. Can only be used when some altitude is present at failure. Not all helos are well suited to this method. Not all pilots are capable of this method. Maintaining altitude (or a slight climb) may only be possible with significant forward airspeed, and only in certain airframes.

Method 3 High Main Rotor torque method. This is the climb out from either low speed or a hover method. This method is used to climb out of a bad landing area at low altitude, so a transition to method 2 can be made. This is the method GulfPLt used in the event of his earlier post.

This method is not well understood at all, and presents considerable dangers. Anecdotal evidence suggests that this method does work at times, but accident investigations show that it often does not work.

There is usually not enough alternative anti-torque available with this method to prevent spinning of the airframe, as spinning of the airframe is considered quite dangerous in a helo.

Pros: Can prevent a forced landing in an inhospitable area during a low altitude failure.

Cons: Requires great skill from the pilot. Requires an airframe, avionics, engines, fuel system, etc, that can tolerate a high torque induced flat spin. Persons can be thrown out of the airframe while spinning if not belted in. (Added in edit) A pilot can become disoriented in a spin. Structural failure of the airframe could occur in a spin. Collision with an obstacle might occur in the spin.

Conclusion

I guess my final conclusion is that not enough has been done to help helo pilots deal with the issue of loss of T/R. Most new or low time pilots are at a loss as to what do if a loss of T/R event occures except to use Method 1 discribed above, and the results of this method are not always satisfactory. Method 2 is highly useful in certain circumstances, but many pilots are not trained for it, and some airframes are not built to use this method without making great demands on the skills of the pilots.

Method 3 does have some merits in my opinion, but the demands on both pilot and airframe are even greater than in method 2. When I posted some of the ideas previously, it was an attempt to think of ways to better improve the ability of all pilots (through airframe improvements) to perfrom a satisfactory recovery from a loss of T/R event. I also don't understand several things related to method 3. Why does a spinning airframe HAVE to be dangerous (apart from not being belted in, and poor directional control near obstacles). FW pilots practice spin recovery all the time. But as GulfPLt pointed out in his post, he had no training in how to recover a helo from a spin. Why are pilots not trained for this? Are there methods to prevent (or at least limit) the pilot disorientation of a spin? Is there any aero-medical research on this?

Reading the other thread referred to by "The Nr Fairy" demonstrates just how daunting this event is to nearly all helo pilots, and it's my opinion that more can done to improve both helo airframes and a pilot's training to help a pilot get through a loss of T/R event safely.

To vfrpilotpb, I took the word "some" out of the text, as you are correct.

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Safe flying to you...

[This message has been edited by Flight Safety (edited 02 July 2001).]

Flight Safety,

I am a reasonably low time Heli pilot covering the range from R22,R44 and B206, here in the UK in order for you to get your Licence you must be able to demonstrate to the Flight Examiner that you are fully capable of enterings and controling autorotaion and to land from that Auto,as opposed to your comment that some knowledge of Auto is taught, however it seems that because of the complexity of simulating T/R failure the only thing that is covered during civillian training is the Cfi jamming the control's so you get some feel of what is going to be the problem of directional control as speed decays, you soon realise that engine speed is the solution to keeping straight, but in the main we civvie pilots are not able to do much more than ask, read and talk to very experianced pilots about the problem of tail rotor failure.
Being interested in this from a selfish , safety of my backside point of view, I would ask that "Ancient Pelican or Nick Lappos" PLEASE give us the benifit of their huge experience in this area (T/R Failure) so some of us less experienced pilots could benifit from their knowledge , possible AP has more than anyone , as this thread has ben told of the total loss of his TR, and he is still posting here, that indicates his ability to comment with authority.
My Regards

Flight Safety,

Your goal is an admirable one, but one critical reaction of a spinning helicoper is the force of airframe drag. When a helicopter spins, in particular, the tail boom and vertical fin (but also the cabin area) act to roll the helicopter over. This is due to the fact the boom and fin are positioned below the level of the rotor head producing a coupling that is detrimental to the control of the helicopter. In nearly every case the helicopter will bank over, as it spins, to the point where either blade / boom contact is made or the disk is tilted to near vertical where it cannot support the weight of the aircraft.

One other point is that in most cases you could not posibly translate from your method 3 to method 2 in a developed spin. The ability of a human to make the control inputs necessary to keep a helicopter upright and accelerating at the same time whilst spinning is basically out of our reach. Not only that, but the rate at which our pilot will be required to go from cyclic stop to cyclic stop will be faster than the rate the control servos will allow, he will now be fighting the hydraulics as well.

The last point may not be as relevent on our modern machines now with hingless or rigid rotor systems etc, but more often than not you will come to grief if you try it in a 206 or 47 or similar.

Enough said, my point really is to highlight the fact that the helicopter will most likely NOT stay spinning in one plane, if power is applied during a tail rotor failure in the hover or at slow speed.

Cheers

Flight Safety,
I don’t recall mentioning SOPs in relation to your comments, however I did feel your remark below was unrealistic:

“What puzzled me was why the pilot didn't apply more collective and climb, so he could straighten it out with a little altitude and attempt a landing on the surrounding flat terrain. I know this would have increased the spin rate, but as long as the airframe structure can tolerate the increased spin, this would have been far better than destroying the helo in the rocky ravine.

So that's my idea, why can't pilots do what "GulfPLt" did, and just climb if needed while enduring a higher spin rate, if that's what it takes to get out of trouble following the loss of T/R, especially at low altitude above an uninviting landing area? “

The following extract from the Uk’s AAIB on an AS355 last year makes interesting reading on this subject:

“…..diverted to a second task which involved hovering at 500 to 600 feet agl over a residential area near the M4 motorway. The visibility was good with a last reported surface wind of 200°/12 kt. Sunset was at 1910 hours and daylight was fading, but the pilot was still able to fly by visual reference.
The helicopter had been hovering in the area for about 10 to 15 minutes, facing in a south-westerly direction, when it suddenly made an uncommanded yaw to the left through some 180 degrees. The pilot immediately applied full right yaw pedal to counter this yaw. However, although the helicopter stabilised for a moment, it then yawed more rapidly to the left. At this time he called out to the two observers on board to warn them of a problem with the helicopter. He partially lowered the collective lever in an attempt to regain control and applied some forward cyclic to gain forward motion and airspeed, but the helicopter then entered a steeply spiralling/yawing descent to the left. The pilot realised that he would not be able to recover full control of the helicopter and abandoned his attempt to fly out of the situation. He concentrated on keeping the helicopter as level as possible whilst looking out through the right side window for visual reference, since he found the forward view too confusing due to the rapid yawing motion. He adjusted collective to achieve what he judged to be the best combination of rate of descent against yaw, and when he caught sight of the surface in his peripheral vision he pulled the collective lever fully up to cushion the impact. “

(Full report at; http://www.aaib.detr.gov.uk/bulletin/jan01/gsaew.htm)

So, I was not intending to cause offence to anyone, merely to add some words of caution to those on this thread who profess to be low time and in search of wisdom. Mind you, most of us are low time when it comes to TR failures, and long may that continue!

As has been said ( I think I may have done too, but obviously in invisible ink) in a teetering head design the resulting fueselage movements that might ensue following a high rate of yaw, could and probably would result in main rotor contact and break up.

The advice of Test pilots is invaluable without doubt, but remember also that any deliberate examination of handling characteristics in this regime will be done in a controlled and systematic approach following extensive briefings and simulations. They are of well above average skill and in current practice with handling extreme situations. Your average line pilot who may not have done even an autorotation for many months or years, and at the end of a hard days flying will probably have a very tough time indeed dealing with a loss of TR drive, in any flight regime, unless in the cruise in a Dauphin perhaps.

You may get away from a TR failure in one piece, on the other hand you may not; it depends on many factors not the least of which will be LUCK!


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Another day in paradise

Also culled from the same report 212man got his bit from :

"Prior to joining the company he had flown helicopters in the Royal Navy for a number of years. In 1993 he was involved in an accident to a Westland Sea King helicopter in which the tail rotor drive shaft had failed. He had witnessed, on that occasion, a change in engine sound or mechanical noise associated with the loss of control, whereas on this occasion he had not heard any such changes."

Prior experience counted for him when he had his second problem !!

Thanks 212man. I apologize that I reacted as strongly as I did, and I understand your desire that no one be misinformed, especially the new and low time pilots. I'm glad we're still friends. :) :)

I agree with your comments and I understand the decision made by the pilot in the accident report.

One think that still troubles me is why loss of anti-torque spins in helos are so daunting to most pilots. In FW flying, aircraft have to meet design certification requirements for spins, and pilots have to be trained in spin recovery techniques. Why is it that airframe design for spins and pilot training for spins is such a relatively "unexplored" area in helicopter flight (other than "lower the collective, chop the throttle and autorotate")? Is it because the "egg-beater" can be sat down anywhere (which is only a partial truth because in reality it can't be sat down just "anywhere") that not much effort has been put into "flying" spin recovery techniques?

I also want to look at the FARs (when I get some time) for helo certification, to see exactly what the certification requirements are for alternative anti-torque and spin stability, and to see what requirements actually exist.

For what it's worth, I think more work needs to done on method 2 listed above (the low/mid torque, run-on landing method) so that this loss of T/R recovery method is not nearly so daunting to most pilots.

I guess after seeing the ANG Blackhawk (loss of T/R) crash video last year mentioned above, I just started thinking that other alternatives have to be available other than just entering into a flat spin, and accepting the fact that you have to go down in a totally inhospitable area, that for those pilots and crew just destroyed their helo and seriously injured some of them. What was weird is that while the spin before descent was brief, it didn't really look that unstable. The helo just hovered for a moment, in a nice (not too rapid) flat spin before it started descending, and the descent was pretty flat as well.

It's the characteristics of these flat spins that I don't think are very well understood, and a "flying" recovery from these spins certainly isn't well understood. The only recovery method that is fairly well understood is the "autorotate, you're going down" recovery method.

It's what guys like GulfPLt were able to accomplish, that make me think that loss of anti-torque spins don't have to be as daunting as we perceive then to be now. I'm just hoping that research and investigation can provide some better options in the future, as the options we have now for loss of T/R recovery are pretty limited in my view.

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Safe flying to you...

[This message has been edited by Flight Safety (edited 02 July 2001).]

I'll start by saying I think from Gulfplt's description that it was a partial loss of T/R control. Not so?

My experience has all been simulated thus far, in the simulators at Bell/FlightSafety (FS) in Fort Worth and with the Canadain Military (CF) in Gagetown, N.B.

It was mentioned before that FS's assessment of vertical stab effectiveness was optimistic. The CF agreed and adjusted their aerodynamic programming accordingly. In the sim the response was pretty basic, lower collective, roll off throttles if you have time to think about it, and cushion at the bottom. Like most of these items, practice allows you to land something that was extremely difficult the first couple times.

I have also simulated countless stuck pedals of varying degrees in the hover, climb, cruise, descent, even on the ground prior to T/O. This is in the RH22, RH44, and BH06. I have seen several pilots try to pull pitch and climb away when the right yaw got away from them and they wanted to go around and try it again. I make a point of maintaining the failure, just so they can see why this is such a lousy idea.
Invariably the right yaw accelerates beyond their ability to focus on the horizon and they lose the ability to maintain a level aircraft, any wind/airspeed and associated weathervaining only exacerbate the situation as the tail whips through 90-180ish yaw. I rarely let it go more than one full rotation and never yet has the pilot thought that I took it too early. The reaction I teach in this situation is to stop the a/c (cyclic flare to zero groundspeed) and perform the failure as per the hover. They are already close to ground now so it's a short hover chop to the ground.

I would love the opportunity to get in a light helicopter sim and compare rotation rates with what we get for varying aounts of stuck right pedal in the hover. What I generally use is a stuck right pitch sufficient to maintain a right rotation in the hover despite immediate closing of the throttle.

Now, to respond to soem comments above:

Spins: A fixed wing spin and a rapid yaw are two completely unrelated beasts. The autorotation is the closest rotary equivalent to a plank spin, and is handled quite well. Control in the spin gets quickly out of hand because you are sitting out in front of the center of rotation, trying to look at a world that is moving too quickly to focus on. The immediate (normal) reaction is to focus in tighter to the a/c to pick up details, taking the horizon out of the picture, and pitch control gets ugly. Additionally, if the a/c is rotating at, lets say, 60 RPM, easily achievable, then the RRPM is effectively 530 - 60 = 470 RPM (this is for the R22) or 89%. For the R44 it is 85% and the 206 it is even less. Even more pitch is now needed to effect that climb, meaning more power, a higher rotation rate, and a lower effective RPM. Overtorque or overpitch follow and game over.

Running Landings: Nice if you have a place to do it I guess. Here we rarely fly in anything close to hospitable terrain and always teach a spot landing using cyclic flare and landing as per failure in the hover. When I was on mediums in the IFR world the running landing was standard but there is a lot more machine to toss around.

Of course, these are my opinions, they won't cover every situation, and feel free to disagree and tell me so.

I have to say I'm with Nick's last sentance.

I've been conditioned to treat a anti-torque failure as an immeadite auto condition, as at this pint I've not the skills (I may feel differently later on as I gain experience) to try to continue flight with the condition. Also, once established, adding small amounts of power as he stated withthe "glide extention" could be done.

But I love reading the varied respnses here on this thread !


Nick,

Tell us more about the Commanche!

Am I correct in that it is single stick for cyclic and you rotate it for tail inputs?
(this I have heard and cannot confirm)

It seems to be a joy to fly ..... I missed gettin gto see it when it was brought down to Ft. Laud beach.

I'd love to fly up to Vero to get a once over, but alas ..... http://www.pprune.org/ubb/NonCGI/frown.gif

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Marc

[This message has been edited by RW-1 (edited 03 July 2001).]

Helo teacher,
exactly! The FSI sim at DFW (not the level D one, I can't comment on that) is far to easy to control. I even carried out landings on the aircraft carrier at night in it (for fun) after taking off and losing the TR gearbox at 60 kts on climb out. Very ego boosting but not realistic.

On the other hand, the level C+ SAS 212/412 sim at Stockholm is great; you are upside down and wirling like a Pitts special in a flick roll if you don't dump the collective AND roll off the throttles (good lesson for those who friction too tightly).

Also as you say (and I did too), the transition from seemingly controlled flight to total loss of control when dealing with stuck pedals, is very rapid and needs to be well understood (before hand) as you are then in a really bad situation.

Must go, I'll have think about the FW spins but I don't have time now. I any case the aerodynamic loads will be considerably less.

------------------
Another day in paradise

I also forgot to add that at least in the cicare simulator (a full size flying sim itself that volar has, uses a rotax to power it) I can experience either a T/R control failure, or a full blown loss of tail rotor failure without worry of killing myself, this is one of the good things about that simulator, which is really a one person heli in a "frame", which I described some time ago.

So while I may not try to fly out of a full blown tail rotor loss, I might at least not be panicked when it happens having experienced the sudden quickly developing yaw.

For a pic of it and description, go to:

http://orbita.starmedia.com/~cicarehelicopteros/



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Marc

Flight Safety,

For my sins, I am a helicopter and aeroplane instructor and have demonstated and taught low level aerobatics in both aircraft categories.

In a stiff wing spin, depending on the aeroplane, the pitch/roll/yaw rate is actually relatively slow. However, the pilot is unable to control the attitude during the spin and the aeroplane generally consumes !!!!!loads of altitude while you sort it out. After gross anti-spin control (remember that all controls are still working) defeats the spin, one then recovers from the steep nose-down unusual attitude and flies away. Alternatively, you eject/parachute/strike the ground.

In a helicopter, life is considerably different. If one loses T/R authority in the cruise, there is a reasonable chance of keeping it all together. If it happens in the hover, the onset of rotation is rapid and eye-watering. Unlike our aeroplane, the helo pilot must make control inputs to maintain some semblance of a survivable attitude - the machine has no inherent ability to keep all of its bits in the intended location.

Here is the scene: the helicopter has started to spin rapidly at the torque currently set and the options are:

a. reduce the torque and slow the spin in order to bring the reaction time for survival manoeuvres closer to your capabilities, or

b. increase the torque substantially to generate vertical movement, knowing that one will dramatically increase the yaw rate and the demand for control inputs that are required simply to keep the rotating bits between you and the sun. In most cases, this requires a conscious move to take the reaction time for survival manoeuvres further from your capabilities.

Now I reckon 'b' is a poor option unless, as I have found myself, falling into the mouth of an active volcano is the only alternative. In that case, sangfroid is but a dream.

I used to teach loss of T/R authority in the high hover, simply because the almost automatic entry to autorotation created its own, very real, problems. Thus, the height took all the fun out of a relatively straightforward recovery. Suffice it to say, the control motions required to keep the sunny side up while trying to gain sufficient forward speed to alleviate the rotation and permit either a running landing or some sort of fly-away manoeuvre were always illuminating, both for me and the victim.

And one could never ignore the gut feeling that both Mr Bell amd Mr Robinson's mast stop margins were always threatened to a point that neither could have contemplated.

Bottom line - the only similarity between F/W and R/W spins is that a rotation is involved - that is all.

------------------
Stay Alive,

[email protected]

just wanted to comment on the chute idea mentioned a ways back - a possible problem with this idea is the overall increase in parasite drag which will slow the machine down (which isn't preferable in TR failure situations) to maintain speed then requires an increase in pitch/power which in turn increases torque - and your yaw problem.

I've been busy the last couple of days, and been wanting to add some final comments about this. I want to add how I think the run-on landing method (method 2 listed above) can be improved for any helo, and how a possibly safe way of conducting a high torque climb after loss of T/R could be accomplished (method 3 above). After this post, I think I'll be finished with the subject.

Regarding the possible future improvement of the run-on landing after loss of T/R, Nick made the following opening statement in his very excellent post:

He then followed with an excellent discription of how to enter into this form of recovery. My focus however will be on his opening statement.

We all know that he's very correct in his statement about the size (or area) of the vertical stab being limited, but this raises the question of whether other possible means of increasing the aerodynamic anti-torque of the airframe might be available aside from the vertical stab. One possible solution would be to use something like FW delta fins mounted in rougly the same position as they are on FW aircraft, that is under the tail boom near the rear.

Here are the reasons why I think delta fins might work to improve aerodynamic anti-torque on a helo. If they were mounted at an angle that was more vertical (down) than sidways, then they could serve as additional sources of vertical stability (anti-torque) on the helo in forward flight. These could then replace the vertical area lost to the restrictions placed on the vertical stab, since being mounted under the tail boom would place them out of the airflow path for the tail rotor. Size (area), placement, mounting angles, and distance from the end of the tail boom (the moment arm) could all be determined by computer simulation, wind tunnel testing, and flight test.

Delta fins could also solve a couple of other problems. Being mounted under the tail boom, they would not pick up much rotor downwash like the horizontal stab on a helo sometimes does, and therefore would not contribute much to a pitch problem in hover. Delta fins would offer very little drag in forward flight, thus the normal aerodymanics of the airframe in forward flight would be little effected by them. There's also the possibilty that the range of the helo could be extended slightly, if the anti-torque provided by the delta fins is more efficient than that provided by the tail rotor in forward flight. If so, then power diverted to the tail rotor for anti-torque could be reduced in foward flight, thus adding a little to the range.

One possible problem with delta fins is what effect they might have in crosswinds, since the area of the side of the tail boom would effectively be increased by them. The test methods mentioned above could determine this possible effect.

Increased vertical area provided by delta fins could help a lot with providing alternative anti-torque in the event of loss of T/R, and might make performing a run-on landing much easier to accomplish.

Now to go on to the issue of trying to make a high torque climb safer following loss of T/R.

Several facts were pointed out in these posts that are very good points. Someone pointed out that drogue chutes are really useful for spin recovery in FW aircraft during flight test. Nick and I exchanged a brief e-mail where he pointed out to me the problems of using a drogue chute, especially as a "fly home" device because of the excessive drag. He also pointed out that the increased drag only adds to the anti-torque problem. He did however point out that a drogue might be useful in spin recovery.

Someone else pointed out that the vertical stab on a helo can impart a roll to the helo airframe if it's in a main rotor torque spin, since side air force on the stab would provide a lever arm rolling the tail boom from top to bottom.

So here's how I think a high torque climb following loss of T/R might be made safer.

The delta fins mentioned previously could offer an additional advantage in this scenario. They could offset the area of the vertical stab in a main rotor torque spin, by offering air resistance BELOW the tail boom roll center, thus offsetting the lever arm of the vertical stab. This issue could be addressed at the same time when designing delta fins for the foward flight anit-torque problem discussed above. It should be possible to design the delta fins so that the moment arms of the fins and the vertical stab cancel each other out in a main rotor torque spin. Adjustments in the area of the vertical stab and delta fins could be made so that there's no roll component at all in a main rotor torque spin.

Besides delta fins, the next item I think is needed to make a main rotor torque spin safer is a drogue chute. This could work by using the chute for what it's historically been good at, spin recovery.

Someone pointed out the disorientation of the pilot in a spin, especially the faster it gets. Someone else pointed out that there would be a loss of main rotor RPM in a spin because the speed governor's RPM reference is to the airframe, and if the airframe is spinning, the governor would slow the main rotor RPM in response.

The droque chute could be the solution here. It would have to be mounted at the end of the tail boom (to maximize the lever arm) and at the roll center so it wouldn't produce its own roll component in a spin. Poping a drogue chute could significantly slow down the rate of a torque spin because of the anti-torque that it would provide. Thus it might prevent a significant main rotor RPM loss, and prevent pilot disorientation.

The size of the chute would have to be determined by the test methods listed above, and the tail boom might have to be strengthened to handle the shock of the chute's deployment (it's already been designed to handle the standard anti-torque loads).

With delta fins and a drogue chute, I see a future hypothetical high torque climb working something like this:

You're hovering at low altitude over a forest doing logging work, when suddenly the T/R losses all thrust. You could autorotate into the tops of the trees, or you could climb out and try to fly it to a run-on landing.

You quickly decide to climb out. The spin must be at least partially established so the chute will fill upon deployment and not get foiled. You won't have to to wait long, as the spin will already be established by the time you decide to climb out. So you hold the collective where it was previously in the hover, hold the cyclic in the center, and pop the chute.

The spin stabilizes quickly and you apply small collective inputs, both to compensate for the slightly lowered main rotor RPM and to start a slow climb, as a slow climb lowers the anti-torque requirement and produces a slower spin rate. You also continue to hold the cyclic in the center to keep the rotor disk flat. Forget about directional control as you won't have any, you'll just drift with the wind during the climb. If you start drifting close to an obstacle, you might have to think about increasing the climb rate to avoid it, but only if absolutely necessary. The only instruments you can count on in the spin are the baro altimeter and perhaps the VS indicator to monitor the climb.

When sufficient altitude has been reached to transition to forward flight, it's time to terminate the climb and exit the spin. To do this, you lower the collective to start a brief autorotation. With no main rotor torque the drogue will quickly slow the spin and as the spin slows to a stop, you apply forward cyclic to start forward airspeed. This should be done before the spin stops completely as again you want to keep the chute filled so it won't foil. The chute should help to keep the pointy end forward as airspeed builds up. When airspeed is sufficient so that aerodynamic anit-torque provided by the vertical stab and delta fins can take over, then you can jettison the chute and fly to a proper location to perform a run-on landing. (My instincts tell me however that this spin recovery would be a little more complicated than presented here, due to the nose down moment caused by the chute when the collective is lowered).

I know this is very forward thinking, and if I had an R/C model helicopter (which I don't), I'd modify it to at least test the basic aerodynamics of these ideas (the human physiology aspects aside). It would need a channel to neutralize the tail rotor pitch (to simulate the loss of T/R), a channel to pop the chute and a channel to jettison it.

Gee I wrote a book, sorry about that guys.

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Safe flying to you...

[This message has been edited by Flight Safety (edited 06 July 2001).]

By chance, I'm at the stage in my 155 course where we covered TR problems today. It has to be said that the Fin on a fenestron a/c makes the whole process infinatley easier than a conventional type, though it does require a reasonable amount of space.

I was pleasantly suprised by how controllable the final touchdown was, and the benefit of right roll to reduce the speed still further before the nose aligns with the runway.

Definately no need for an auto with this one.

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Another day in paradise

Some fun from my model bretheren (I have 2 heli's myself)

Hehe, these guys decided to stop the rotor while doing an auto, and figured they would still have enough negative collective pitch (which models do have) to recover. I had stated that they would lose the bird, not from exceeding crit AOA on the blades, but because they would suffer blowback as the model then accellerated with stopped blades.

Well I'll let you see the video:

http://ronlund.com/hhsmall.avi


Blades departed shortly after stopping :)

Heli: totalled., a bummer, but made a nice video.



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Marc

212man,

Presumably you are referring to in-cruise failure? Or did you deal with fenestron failure in the high hover?

------------------
Stay Alive,

[email protected]

4dogs,
yes, in the cruise followed by run on landing. Obviously in a the hover you'd be pretty poorly placed and would need to lower the lever and acept the yaw (can't "chope throttles in this one").

Hi Peeps.

Sorry to join this a bit late! (I've been on me hols!)
Firstly....any tail rotor failure in a high hover is very bad news. Each aircraft has different handling capabilities. I've had two tail rotor 'problems' one was a drive shaft failure & one was a control failure.

The most significant difference was the change in noise. When the drive shaft failed the noise change was obvious, the control failure didn't noticeably alter the noise.

Some have talked of pulling power & climbing. People if you manage it my hat is off to you. Amazing courage. My drive shaft failed at 40' just coming in to land, the obvious solution was to just dump it on the ground & live to fight another day. I lost T/R control at some 550' in the hover.
Should I have climbed? You may think so...I was there & I can assure you it was never an option! The rate of spin may from the outside have looked sedate, but in the cockpit it felt horrendous! The centrifugal force was initially enough to lean me (& hence the cyclic) to the right. Climb & increase the rate of spin???? Forget it!
Some would say chop the throttles & take away the torque reaction! Ha! Forget that! An autorotation from a 550' hover in a As355F2!!! The word SPLAT springs to mind!! No people...I can assure you I had plans for my engines & they were staying right where they were! The best plan I could come up with was to fight the aircraft down as gently as possible! It appears that between Lady Luck & me we did OK. The AAIB described the impact as relatively benign! Oh & by the way to make it benign I used everything BOTH engines had to offer! Chop them??? No way!

Forward flight failures are a different kettle of fish, as are jams etc! The variables are countless!! What I would say is that my military & civil (thanks to the North Sea & a couple of fantastic sim instructors!) proved invaluable! There ia an old addage in aviation.....I won't teach you to suck eggs.....but we walked away.

By the way...with relation to the simulator training....it teaches you what to do in many of the scenarios.....but the sim can never prepare you for the violence of the rotation! Particularly in the high hover, in a heavy aircraft legendary for it's poor tail rotor authority!! :eek:

[ 07 July 2001: Message edited by: Roofus ]

Thankfully I never had a real failure yet, but have lost tail rotor authority on a number of occasions (very slow flight, OGE, well out of wind, strong w/v. A little alarming but easily surviveable).

However, from previous experience as a sim instructor (including an RAF trial on tail rotor malfunctions on the Puma for general guidance of said type's pilots) and other experiences on French and American types (different directions of main rotor rotation), to avoid confusion in my own mind, here are a few rules that I now always bear in mind:

Rule 1: If the tail rotor driveshaft fails I expect an engine off landing either immediately or at some very imminent stage. Note that if this occurs, the (bad) yaw is towards the advancing blade of the main rotor (advancing side is therefore bad, read on). Fly accordingly and be aware!

Rule 2: If the tail rotor suffers another type of failure i.e. cable / control / stuck pitch, aim to keep the nose of the aircraft on the main rotor's RETREATING blade side and set the aircraft up for a running landing in that configuration. That way any increase in collective to cushion the touchdown will bring the nose towards 12 o'clock and with good judgement will give nil or minimum yaw on touchdown. If the nose goes through the 12 o'clock position towards the advancing blade side, increase airspeed and / or go around.

Also, with a tail rotor control problem, if possible keep the wind on the RETREATING blade side on final approach. This gives "weathercock effect" assistance in the correct direction. (Note that this helps offload the tail on ANY normal approach).

Personally, I have always found the American teaching "lucky left / rotten right" potentially confusing as I have alternated between American and French types.

Retreating blade side is ALWAYS lucky.

Hope this helps someone someday!

SC

My first tail-rotor failure was actually a self-induced tail-rotor drive-shaft failure. The drive-shaft jumped out and flailed because the first hangar-bearing behind the jet exhaust (in an Iroquois) got overheated and failed due to a lubrication break-down. The reason the lubrication broke down was because I'd been hovering downwind winching trainee crewmen up and down for over 30 minutes. Not a significant downwind component either -just about 4 or 5kts. However it was sufficient to pool the hot exhaust gases around the No 1 hangar bearing and cause it to seize and jump out.

Of course you could always criticise anyone for hovering out of wind however given that the target was a rock in the middle of a creek and that the only hover reference was out of wind, it seemed a reasonable idea at the time. But full marks to the crewman instructor who cut the cable and dropped the two guys in the creek before we landed on the bank (luckily without spreading the skids). Naturally I got criticised, but up until that time nobody had ever mentioned that particular vulnerability of the tail-rotor drive-shaft. No doubt others have managed to do the same trick since - and others yet unborne will repeat it. It was interesting that I had a buzz of about 30 sec duration (only) through the T/R pedals before it broke lose with a loud bang.

>>Rule 2: If the tail rotor suffers another type of failure i.e. cable / control / stuck pitch, aim to keep the nose of the aircraft on the main rotor's RETREATING blade side and set the aircraft up for a running landing in that configuration. That way any increase in collective to cushion the touchdown will bring the nose towards 12 o'clock and with good judgement will give nil or minimum yaw on touchdown. If the nose goes through the 12 o'clock position towards the advancing blade side, increase airspeed and / or go around.<<

Oh man, that is one rule I will try to incorporate into my memory! :D

Thanks SC!

Tail rotor failures - CAA report
 

The CAA have published a report into tail rotor failures. It's accessible via their web site, here.

It's 255 pages so I haven't yet read it, but I imagine it will cause some discussion. And I wonder if Roofus will start a company dedicated to training t/r failures . . . :D

Wow - some very interesting reading. I only skimmed it - there's a lot to be absorbed from all that analysis.

Thanks for the link!