TR malfunctions for beginners - a refresher lesson!

[MightyGem]

Just to show that it can be done, the(poor quality) video shows a AS355 landing after a tail rotor drive shaft breakage. If you look carefully, you can see a stationary tail rotor. To prevent any doubters asking, we have the tail rotor on our crewroom wall.

Tail Rotor Failure - YouTube

[jellycopter]

MG

Do you have any background on this incident? I use this video in my T/R Malfunctions briefing at work and some more info would be helpful.

JJ

[[email protected]]

As I have said before.....Wokka's and Tail Rotor Failures don't take much discussion.

so why introduce the subject here?

For clarification - small= Gazelle, Squirrel, R22 (at a push because of the low inertia rotor), Jetranger - with good conditions and elements of skill and luck zero speed EOL with no TR feasible and survivable.

Larger - UH1 - yes (big, high inertia rotor allowing a big flare, a high level and enough Nr for a vertical cushion); Wessex - marginal but the tail wheel allows for a lot of nose up whilst protecting the TR; Lynx - no, small disc with great response but the TR would strike first and the Nr decays very quickly. Sea King - no, long tail and no protection for the TR.

[Thomas coupling]

jelly:the AAIB report is online. If you really need info from the horses mouth, I can put u in touch with the pilot. send me your e-mail addy in a PM and I'll pass it onto him.

[[email protected]]

And no attempt at a zero speed EOL, surprise surprise.

[SASless]

So he chose option B....and carried it out quite well.

You reckon he did a handling check and decided Plan B would work?

As to "Zero Speed" which you are quite hung up on.....if you will read the prior posts you will see it was "Zero speed to Minimum/Minimal/slow forward speed".

[cyclic flare]

TC

Your best post to date well done

Cyclic

[Thomas coupling]

Thank you cyclic

[JohnDixson]

TR on Auto Landing

Crab, in the autos done on the S-92 as an example, after leveling, and during the collective application, there was a distinctive right yaw tendency, thus a necessity to add a bunch of left pedal to keep the nose aligned. As I recall, we used almost all of the available range. Of course, the TR Nr is going down and the lift/V squared relationship is in play.

[Thomas coupling]

John,
The speed of the TR doesn't change during an auto?
[Hence why you get yaw in the opposite direction to MR rotation].

In an EOL however...........................

What was your message anyway?


SAS: Please try and remember your heritage Not everyone was born in a helo!
The purpose of this thread was to prepare ab initio's and those 'out of touch' that TR failures / control restrictions are VERY serious in helicopters UNLESS one is VERY familiar with the mechanics.

It is probably the LEAST discussed/rehearsed/trained evolution in the rotary world. AND the most damaging if handled badly

[jellycopter]

TC

I'm responsible for briefing T/R malfunctions on one of the ab-initio squadrons at DHFS. This brief is given prior to going solo and at the first circuits phase.

I split the subject into 2x 2-hour briefs as there's so much to cover!

One brief deals with Yaw Control malfunctions (T/R control failure), the other covers uncommanded yaw incl. T/R Drive Failure.

I have found that the best way to foster a depth of understanding wrt to 'uncommanded yaw' is to ellicit the possible causes. These include, T/R Drive failure, LTE, Hydraulic Malfunction (we teach on AS350 with Hyd assisted T/R), wrong pedal input and weathercocking. By breaking down each scenario into it's components and likely symptoms and recovery actions the students seem to lap it up. A generous smattering of helicopter porn (relevant accident videos) and accident reports spice things up a bit. It's one of the few briefs that I give where theres a 'buzz' in the canteen during the coffee break.

There have been numerous training accidents worldwide (IIRC incl 2 at DHFS) as a consequence of poorly handled yaw. Rarely was there anything wrong with the helicopter. Understanding, recognition and correct diagnosis are the key to a successful outcome.

JJ

[SASless]

This part of your post I fully agree with.

TR failures / control restrictions are VERY serious in helicopters UNLESS one is VERY familiar with the mechanics.

It is probably the LEAST discussed/rehearsed/trained evolution in the rotary world. AND the most damaging if handled badly

The other thing I see wrong is too many folks fail to understand just how much "Yaw Control" they do have even when the "normal" control system is not working as it should for any number of reasons.

[Thomas coupling]

JJ, I've heard you do a very comprehensive TR brief, both from MG of the long moustache clan and from AH

[[email protected]]

John Dixson - I am curious, the S92 autos should have required 'non-power pedal' as the Nr reduced on an EOL which would have been right pedal for a counter clockwise rotor.

With a power assisted 'flare recovery' I would expect power (left) pedal to be required but if the engines are shut down or at ground idle, the opposite should be true. I base this on many years of Gazelle (clockwise rotor) EOLs where lots of left(non-power) pedal was required during the Nr decay phase of an EOL.

[MightyGem]

there was a distinctive right yaw tendency, thus a necessity to add a bunch of left pedal to keep the nose aligned.

Transmission friction? (If I've got the blade rotation direction correct).

[RVDT]

For those with failing memory and in answer to the question lets roll back 5 years or so.

ATPL Theory Question

On helicopters with a large fin (fenestron) be a bit careful about getting too slow. Life gets a little interesting if you get in a position when the thing stalls suddenly.

Those of you that are fortunate enough to have access to a sim should try an OGE hover and get the instructor to drop the TR off line. Prior to this it is your call as to what height you think you can recover to straight and level from.

Answers on the back of a postcard please.

[Thomas coupling]

Whatever happened to KISS

[[email protected]]

RVDT - at least 1000' - and that is to get enough control to make an EOL, not to recover to straight and level (because I don't think you can unless you have a big tail fin).

[JohnDixson]

Nose Right

MG, that was our understanding as well.

Re the large vertical fin/fenestron stall observation: the solution there is akin to the solution for keeping LTE off the table for a particular machine: design for a higher standard of available tail rotor thrust than the minimum FAA crosswind landing req'ts would lead to. Much higher. Hence as an example, the RAH-66 was designed to ( at mission weight ) fly level at 80-100 KIAS, do a snap 90 degree yaw ( either direction ) and hold that heading whilst flying sideways at the entry speed. Mr. Lappos demonstrated that capability to the Eurocopter Chief Pilot in the S-76 fan-in-fin demo machine at the Paris Airshow. In fact he went a bit further and went around to flying backward, all the while staying in formation with me ( flying a UH-60 ) doing the heliroute from Le Bourget back to Issy. We took video from the Hawk. I do not recall the last name of the Eurocopter Ch. Pilot, but he had just put on a spectacular demonstration in their Panther. Nick said that his guest looked at him, smiled, and said one word: " formidable ".

[Spunk]

TC`s way of explaining T/R failure and/or T/R malfunction reminds me of my old flight instructor who taught me the very same way. This plus the ongoing discussion about whether it makes more sense to do it one way or the other reminds me of the most important lesson some of us tend to forget:

• maintain aircraft control
• analyse situation
• take proper action

If you can't slow it down to a speed suitable to make a running landing you better start looking for an alternative solution.