Medium Tail Rotor Drive Failure

[splitpin]

In all my years flying I never had an emergency that I could have trained for, they always seemed to happen at the most inapropriate time and it was basically responding to a situation and survival. My biggest concern was knowing what the machine I was flying was capable of doing and each machine was different, even the same category and model.

 

Back to my Navy days, we had recently overhauled HUP-3 Piaseki (year prior) in the hangar doing 300hr. inspection. One of the checks was to put the rigging pins in the heads to check that all controls were at the required settings. Upon lifting the pichhorn on the M/R head the unit came up and would not go back down to fit the rigging pin. Checked in the cockpit and found that the screwjack that contolled the pitchchange mechanism was off it's mount on the transmission.

 

Without going into to much detail, the main rotor system is controlled on both heads by screwjacks mounted on the respective transmissions, the screwjacks go up and down controlled mainly by the collective (initial power setting). Inside the screwjacks is a locknut that prevents the screwjack from coming of the stud mounting on the transmission.

The locknuts had never been installed at overhaul and nobody had ever pulled the collective to it's maximum IN THREE HUNDRED FLIGHT HOURS, TALK ABOUT THE GOLDEN HORSESHOE.

 

I guess what I'm trying to say is, a person reacts to a situation in what he/her has been exposed to, if you have time.

 

Don

 

Don:

You didn't mention the three chain sprockets on each screwjack. I remember checking the rigging on those screwjacks as well. What a maintenance nightmare!!

Why don't you PM me when you get the time. Our paths have probably crossed as there were not a lot of guys that worked n the HUP-3.

[CTD]

There are a couple of things missing in this thread.

 

First, it is impossible to simulate a tail rotor drive failure with any accuracy. This was explained to me by Nick Lappos himself. The reason being that the tail rotor, when turning, is 1.4 times the fin area of most modern helicopters. So if that tail rotor is stopped, there goes almost 75% of your keel affect. No combination of speed/power will maintain forward flight. Hence the reason most RFM's call for autorotation in case of drive failure.

 

A tail rotor control failure on the other hand leaves the keel effect intact and it MAY be possible to maintain forward flight.

 

Second misnomer is people trying to duplicate emergency flight characteristics with ANY commercial simulator, including level D. Again, Nick says that even research simulators used by the manufacturer are not 100% accurate when it comes to simulating OEI performance, tail rotor failures, etc. The sims we get to use are nothing more than procedures trainers, great for seeing exactly what gages and instruments will look like in a failure and how to react to them, nothing more.

 

The bottom line is, never develop emergency flight procedures from sim experiences. Thats what the RFM is for.

 

Hey Outwest, good to see you around. You're 100% correct in your statements regarding simulators, but your source has led you astray a little.

 

The reason it is impossible to simulate a tail rotor drive failure with accuracy has nothing to do with keel effect, or any other aerodynamic function. Simulators are programmed from flight test data, which is expensive, and only exists for what's inside the four corners of the flight envelope and a very small percentage beyond it. Since we don't traditionally get flight test data for tail rotor failures, at least not on purpose, simulator fidelity for these scenarios is based on predictions.

 

In my former life, I have flown CRJ and Challenger sims to do high altitude stalls and takeoffs with degraded performance due to surface contamination. BA's Flight Test folks reminded us constantly that the sim fidelity and performance for those flight regimes was not accurate, and the tests proved to be almost useless for what we wanted to achieve.

 

Additionally, research 'simulators' used by manufacturers are not big boxes they strap themselves into and virtually fly around in, but computer models.

 

All that said, your assessment of how we should treat sim training is spot on.

 

Cheers,

 

BV

[Guest Jerry]

I would agree that some sims may not accurately replicate aircraft behaviour in certain exercises, but ...

 

When we did the initial civilian certification of the CF 412 (Griffon) sim in Gagetown I suggested that the loss of t/r components in forward flight exercise seemed a liitle mild. A couple of years later they lost a Griffion due to a t/r blade failure and subsequent loss of the 90. The crashed a/c was equiped with HUMS from which they downloaded the actual crash data. Using that, CAE reprogramed the sim to more accurately reflect a/c behaviour. She's a bit of a handful now, as many can attest, but if you do it right ...

[CTD]

I would agree that some sims may not accurately replicate aircraft behaviour in certain exercises, but ...

 

When we did the initial civilian certification of the CF 412 (Griffon) sim in Gagetown I suggested that the loss of t/r components in forward flight exercise seemed a liitle mild. A couple of years later they lost a Griffion due to a t/r blade failure and subsequent loss of the 90. The crashed a/c was equiped with HUMS from which they downloaded the actual crash data. Using that, CAE reprogramed the sim to more accurately reflect a/c behaviour. She's a bit of a handful now, as many can attest, but if you do it right ...

 

Hmmm. The FDR would have given them some lateral acceleration data from HUMS, but they'd have to have been lucky to tag the accident sequence with the sampling rate. The other HUMS parameters would have been pretty much useless for sim programming - if I remember correctly it sampled radial and axial vibration on the tail rotor as trend monitoring only. It's been a while.

 

And even then, you have a snapshot of how that particular aircraft behaved, at that gross weight, c/g, Hd and airspeed, and all FDR data will be corrupted by the actions of the crew.

 

Still, if it's a handfull, it's probably fairly representative of the real thing IN A GRIFFON. The 212 is a different beast, and the use of this sim for 212 training is just plain wrong.

[Hazy]

They would have a timeline for all excedances as they were trying to deal with the tail rotor failure in the CH-146 equipped with HUMS. There is retrievable data in HUMS and in the CVFDR . H

[Guest Jerry]

Thanks very much for that information, CTD, it is most interesting indeed.

 

My comments were based on information provided to me by CAE and others. The complaint (from some) was that maybe the CAE programmers had gone too far the other way.

 

In any case, I am a very strong supporter of sim training; and while we are certainly light years behind the f/w guys, we are making progress.

 

Finally, I think that an imperfect sim is still a lot better than trying to teach some of this stuff on a/c.

 

Thanks again for the informed comments.

[CTD]

The complaint (from some) was that maybe the CAE programmers had gone too far the other way.

I'm not sure that's possible

 

In any case, I am a very strong supporter of sim training; and while we are certainly light years behind the f/w guys, we are making progress.

 

Finally, I think that an imperfect sim is still a lot better than trying to teach some of this stuff on a/c.

I agree with you to a point, Jerry, but since most of us experience a direct reversion to our training when confronted with an emergency, we must be very careful not to 'negative train'.

 

The CH-146 and the 212 share almost nothing, except a basic silhouette and different variations of the PT6-T.

 

- The handling qualities are different in many ways, partly because of the four v. two blade characteristics, but also for certain procedures (i.e. must switch off APs during run-on landing in 412)

- The autopilots are different. The SPZ-7600 and Bell AFCS could not be less similar. The Sperry system found in a handful of 212s shares little more than heritage with its SPZ cousin.

- The fuel system is different. The 412 has 10 cells and transfer pumps, the 212 has 5 cells and jet pumps.

- The AC electrical system is different - 3 inverters vs 2.

- All engine and transmission performance limitations are different

- The hydraulic and governor switch placement in the CH-146 is different than the 212 or 412, and the fuel panel in the 412 / 146 is different than the 212.

- Engine / mast torque systems are different.

 

With this many differences in the propulsion, electrical, autopilot and fuel systems, coupled with dissimilar handling qualities, certain emergency procedures, and cockpit layout, I see the potential for negative training. At this point, the box becomes little more than Microsoft Flight Sim X (said with tongue planted firmly in cheek), and basically becomes a full-motion Level C IFR trainer.

 

I have flown the 212, 412 and CH-146, and will admit to bringing well-trained 412 habits into the 146, and back into the 212. They are two different type endorsements for a reason.

 

Really though, the Gagetown thing was all about saving money, not trying to provide better training. An adequate 212 sim resides in Dallas, but that's farther away and this whole arguement took place in the day of the $1.65 US dollar.

[CTD]

.

[rainman]

Well I must add my 2 bits.

 

We have flown the sim in Gagetown for 3 years now for our recurrent training. Yes there are differences from the 212 but, would it not be much more usefull to see what certain emergency's look and feel like? I agree with Jerry that the sim is a great tool for us as pilots. If you can pull 810 degrees OEI in the 212, (straight 3's) Then that is what we limit ourselves to in the sim. Overall though, the point is very simple in my mind. It's better to experience actual engine fires, followed by engine out, followed possibly by a T/R drive shaft failure to the ground. Not to mention High side gov failures, 90 deg gearboxes coming off in flight, pencil shaft failures. Anyone who ever gets one of those who hasn't seen it in the sim is in for a handfull, (Not to say we wouldn't be as well).

Doing these exercises on A/C involves talking about but not actually seeing it, seeing the turbine temp at 950 because you can't figure out WTF is happening( pencil shaft failure).

I appreciate the differences technically between the two types. I don't feel it is negative training at all, it just prepares us a little bit better for the real thing.

[Outwest]

I may not have made myself clear in my first post.

 

Engine malfunctions, engine fires, pencil shaft failures, electrical malfunctions, IFR procedures, etc, etc are all very good value and what a sim does best. My point was strictly to do with flight characteristics. I have witnessed companies introducing specific emergency flight procedures that they felt were justified from sim experiences. Let me be more specific, VTOSS for example is clearly defined and stated in the RFM, however people have found that in the sim they can achieve a positive rate of climb at values far below published VTOSS and have then put this into practice at the sim and even stated it in the SOP's. THIS IS WRONG. What you are doing in this case is teaching someone how to survive in the sim and then they think that the real a/c will act the same and they get into a mess of trouble.

 

That is what CTD means by negative training.