Courting disaster by "demonstrating" Vmca
 

It is well known that requiring a student to fly a Vmca "demonstration" in a ME aircraft to prove some sort of competency is fraught with danger of mishandling and all the potential for a spin. Colleague described how he was instructing on a C310 where Vmca was being conducted by the student. You know the sort of thing - instructor demonstrates - student practices until certified competent.

A fraction of a second after the nose of the Cesnna 310 began to yaw after the limit of the rudder had been attained, the aircraft went into a vicious spin so quickly that the instructor was completely caught off guard.
After several turns in which considerable altitude was lost, standard recovery action finally took effect and the aircraft bottomed out 1400 ft above terrain leaving three very frightened occupants. However the box marked "VMCA tested" was ticked off of course.

My bet is that scenario has been repeated a thousand times in different light twins, yet from what I can judge the Vmca exercise is a mandatory part of initial multi-engine training. If a fully developed spin is considered an aerobatic manoeuvre and few light twins are certified for aerobatic flight, then surely any manoeuvre such as Vmca that risks an incipient and perhaps a dangerous full spin on a ME aircraft should not be part of a training syllabus.

After all, when flying on one engine in a ME aircraft the student can feel the amount of rudder needed to prevent yaw so why "practice bleeding" just to have the student see how close you can fly to Vmca before flicking inverted? Seems pretty lousy risk management to me.

I wouldn't say, in particlar, that the exercise is to show competence in flying at Vmca - it's more to show why you SHOULDN'T fly at, or even near, Vmca.

It highlights the need for flight at or above "blue line".

I, too, would have "ticked the box VMCA tested" - the lesson had been demonstrated (fairly well, I think).

Now imagine the other scenario - where none of the crew of that aircraft had ever done spin recovery training.

I would also say that ALL aircraft are capable of spinning - they're just certified for doing it intentionally - but that's a product liability factor, not airworthiness.

Is there a requirement for the student to fly at Vmca?

I've only just finished my multi-instructor course, and I don't have my notes to hand, but I seem to recall my instructor on the course teaching me to demonstrate Vmca to the student?

I'm not sure that saying that something "risks an incipient... spin" is justification for not doing it. After all, there is risk of an incipient spin any time you do a stall if the student does not prevent yaw, and this is frequently practiced in aircraft which are not certified for intentional spinning.

Airmanship must surely dictate that this kind of exercise is done at a safe height, though, and also with the instructor having sufficient awareness of the dangers that he prevents a situation developing from which he can not recover. In the example you give, where "the aircraft went into a vicious spin so quickly that the instructor was completely caught off guard", this clearly was not the case - but I'd be willing to bet that the same thing will never happen to this instructor again now that he is aware of the danger!

Thanks for sharing, though - the potential for a spin in this exercise is obvious, but wasn't actually highlighted to me when I did the course. It is definitely something I will watch out for when teaching the multi-engine course though!

FFF
-------------

Keygrip.
Risking the neck of students (think of the legal ramifications if someone gets killed) to show them why you shouldn't fly at or near Vmca is similar to feathering both engines to show you the dangers if they don't unfeather.
And I know of one idiot who actually did this while he was conducting an instrument rating test on a Duchess. He made the student try to unfeather one engine with minimum loss of height. I recall the adage about old pilots and bold pilots but not too many old and bold pilots. Unfortunately the instructor on the feathered engine instrument rating test himself died a few years later sticking his neck out that little bit too far.

feathering both engines Bugger me. I hope he was in an Orion.

An interesting lesson to learn for any instructors/examiners who set a bad example methinks... poor guy probably thought he had nine lives.

As for the requirements to demonstarte VMCA - just thought I ought to point out the orginator of this thread is in Aus and FFF is in the UK, in case anyone had missed that. Might be differences in the syllabus?

VFE.

Should we teach - or demonstrate - stalling? spinning? single engine go arounds? PFL's? crosswind landings? unusual attitude recoveries during limited panel instrument flying....they all have inherent dangers if you screw them up.

A lot of the things we demonstrate are to show why you shouldn't do it.

Just simple stalling, for example - we don't teach you to DO it, we teach you what to do if it happens!!

Vmca is the min dynamic "recover and maintain S&L constant speed" speed for sudden complete failure with gear up and everything else in t/off position - there's no requirement to even demo this in the UK.
All control demos are steady state:

1. start at Vyse, gradually throttle back an engine, slow down until a control reaches a limit or Vs+5 reached. Recover by retarding live and lowering the nose before throttling-up both
2. as above but at zero thrust
3. as above with gear and flap
4. as above but at 3-5 deg of bank to live

The only dynamic demos are done well above Vmca: initial failure demo, EFATO, Vtoss.

IMHO fooling around with dynamic failures near to Vmca is asking for trouble and accomplishing nothing -especially if the aircraft is allowed to stall, which must have happened in the situation cited by Centaurus.

BTW, I spend lots of time teaching spinning and aeros in a variety of aircraft but nothing with lumps of mass (ie engines) on the wings; have we anyone here with experience of different spin recoveries for straight winged aircraft with/without wing-mounted stores (or tip tanks)? Most SE aircraft have A<B, it would be interesting to know how spin recoveries change with aircraft when A>B - the info may be useful for recovering a twin.

HFD

A long time ago, as a very low hours PPL holder, when I did all my ME, night and instrument training on a PA39 Twin Comm, most of the time, single engine work was done with simulated zero thrust, but my instructor was very specific about my doing one in flight shut down, a good period of time genuinely on one, and then, the most thought provoking, the restart. We didn't lose any height, but I found my hands had to be flying around all over the cockpit to keep things stable, going in the direction it was meant to be while doing all the other things required for the restart. It was a bit like demeted wall paper hanging, with changes of hands on the yoke, and such like, just to get it started, warmed up safely and then back in balanced flight, but it demonstrated only too clearly that there was a lot of work involved in what in theory sounded very simple to do.

The end of it all, and I was happy that we spent a lot longer than the mandated 5 hours to "do" the ME rating, was that I spent a couple of years doing a lot of hours all over Europe in what was recognised as a very slippery hot ship twin, most of the time single crewed, quite often IFR and IMC. and I thoroughly enjoyed it most of the time, and the few times I didn't it wasn't the fault of the airplane.

What was even more interesting was several years later going over to the States to do a CPL IR ME. I got put with an instructor who probably had about 20 hours total ME time, and at that stage, I had close on 300. It didn't work, the instructor was not comfortable with the airplane, and even less comfortable with the manner in which I was totally comfortable doing things with it that he wasn't. Cue change of instructor, which solved the problem very rapidly.

Making the student demonstrate handling to VMCA is risky, in that the student's responses are likely to be a lot slower than the response needed to keep things in order, especially on the hot ships like the 310 or the PA39, both of which have a "reputation". We certainly did work close to VMCA with simulated zero thrust when doing some of the IR work, to make sure that I was capable of handling the aircraft at the extremes of the envelope, in the same way as I was made to do work close to the VNE end of the speed limitations, to make sure that I knew what to do if I got there by mistake, which it wasn't hard to do on the PA39. It was all about making sure I could recognise the direction of trends, and take positive timely action to change the trend before it went out of limits, which was (in my book) good instructing.

So, I've flown very close to, but not actually at VMCA, and done the same with VNE, for the same reasons, and as far as I'm concerned, that was and is the safest way to deal with it. Anything beyond that should (if possible, and unfortunately on most GA types it's not) be done in a good quality simulator, and by that, I don't mean Microsoft Flight Sim xxxx, as that's not got the necessary fidelity in flight modelling to allow for extreme of the envelope work.

:hmm:

I seem to sort of remember that Vmca decreases with altitude whilst the indicated stall speed stays the same.
This might explain why I have uncomfortable memories of demonstrating Vmca in a Twin Catastrophy in the Johannesburg GFA one hot summer day.
When the stall speed and Vmca meet or when the aicraft stalls before reaching Vmca things can become interesting in a mild sort of way?
This stimulation of interest becomes exceptionally enthralling if the aircraft in question has tip tanks!:O

A very good point Cavorting'

My understanding is also that Vmca decreases with altitude. On my twin oral test the examiner asked if I'd flow at Vmca and at what altitude. When I said yes and quoted the altitude he seemed a little concerned. Thinking that I was about to get my instructor in the do-do I revised the altitude up a little. At this point the examiner became even more concerned and went on the explain that as altitude is increased the Vmca comes closer to the stall speed, which is not recommended! I have no dought that after my test the examiner had a quite work with my instructor:=

A catch 22 situation if there ever was one!

Vmc and Vmca decrease with altitude when the thrust from the live engine decreases with altitude - thrust is the cause of all the problems. If you have a superdooperturbocharger thingy then thrust may remain constant up to significant altitudes.

I suspect people here are confusing Vmca with Vmc. Vmc varies with asymm power, flaps, drag, cg position, leg strength - and probably something else that I've forgotten.
... Bottom line is to close the live throttle and lower the nose whenever you reach a control limit or get within 5kts of the stall.

HFD

Those that "practice" Vmca flight just to see how far the aircraft will go before it flips inverted at full power on one engine (and instructors who enjoy the challenge - if you can call foolishness a "challenge") are around - could also consider another risky manoeuvre - and that is failing one engine in a light twin during the take off run. We all know it requires instant corrective rudder while simultaneously rapidly closing the live engine throttle.

The danger in this particular manoeuvre lies in the possibility mishandling - or if you like, slow reaction - on the part of the student. In fact the student's corrective action must be perfect and instantaneous at first go in every respect. In that case what is the point of practicing the manoeuvre?

A colleague who remarked somewhat ruefully that his students had run off the side of the runway countless times in his instructional career because of their slow reaction in countering the sudden full power yaw when he cut the mixture to one engine during the take off run. Who knows what side loads the poor nosewheel had applied to it? And was this reported in the maintenance document? I very much doubt it since to inspect for nose gear side strain is an expensive business involving in some cases jacking the aircraft up for retraction tests.

Surely the risks involved and clearly demonstrated warrant calling a halt to this high risk manoevre. If high fidelity simulators were available for these aircraft the high risk manoeuvres in the actual aircraft would be banned from the syllabus.

Deliberately failing one engine on the take off run in a light twin is unwise and some might say poor airmanship. A thorough briefing only is needed - not a real life test of how close the pilot can get to a ground loop without a landing gear strain or collapse?

I could not agree more Centaurus!
This (simulated engine failure on take-off) is supposedly a mandatory item on MEPL tests in the UK but is not something that I do - it's a bit like practise die'ing (sp?). If an engine genuinely fails during the take-off roll then any damage is a consequence of the failure and is in the "sh1t happens" category. The training risk can be totally removed by dealing with this by discussion.

Twins seem to crash for a variety of reasons: I believe there was a Seneca fatal in the US a couple of years ago where part of the (male) pilot's anatomy was found in the (female) pax's mouth? :E
Cause or effect?:hmm:
Perhaps this should be a test item too :E

HFD

:hmm:

Without really raiding my notes I seem to remember that Vmca is quite specific to each aircraft and that it is established under a particular set of circumstances.

Is it defined as the speed at which:

1. At sea level.
2. Flaps in the take off position.
3. Gear down.
4. Max continuous thrust set.
5. Critical engine propellor windmilling.
6. C of G in the aft position.
7. Aircraft at max all up weight.

Control of the aircraft cannot be maintained with full opposite rudder deflection.

It is a very specific speed which is established under the worst go round conditions. If demonstrated at safe height the excercise provides a useful illustration to the student that there is a speed below which he cannot control the airrcaft in the event of assymetric flight.

I've probably forgotten something here but that's the gist of it is from what I remember back in the old days of twin training. It's a useful excercise which illustrates what can happen with slack attitude and speed control in such situations as engine failure after take off or single engined go round.:)

The problem is specifying the safe height. A light twin "departing" controlled flight may need anything from 1500 ft to 10,000 ft to recover from a spin and by then you are in test pilot territory and even he would have a parachute! Surely a well designed computer generated image of a Vmc demo would be a great aid to flight safety especially if it showed what happens beyond Vmc if the aircraft gets away with you.

Meanwhile it would seem prudent for ME instructors to stay away from Vmc especially as normal asymmetric flight requires a fair amount of corrective rudder making it obvious to a student that running out of rudder is not a good thing.

cavortingcheetah:
6 out of 7 :D the gear is up. I assume there should not be so many not's there either;)

FWIW a heading change of up to 20deg is allowed but no loss of height, rudder force should be <770N and roll control force should be <220N with a yoke. BUT, as I said before, Vmca is a DYNAMIC situation involving "sudden complete failure of the critical engine" and has no practical relevance to flight instruction.


Centaurus:
Demos of the need to feather, raise flap, decrease drag and add small bank angle are an essential part of the training and this requires flight close to Vmc but must be stopped when a control reaches a limit or Vs+5 is reached, as I've said before. This achieves the aim of the exercise without introducing risk.

The real safety issue here is stalling when asymmetric, rather than Vmc

The UK syllabus (complete with typos!) is available here: http://www.caa.co.uk/docs/33/CAP601.PDF
HFD

:uhoh:
Darn. I knew I'd make a boo bo somewhere. Never mind. 'Not' removed.:D

Some thoughts ..

(a) Vmca normally is a work up for static values and then checked to make sure that the dynamic failure is not more critical

(b) the sea level value is an extrapolation from the altitude work

(c) playing with low speed asymmetric thrust ... ie near stall ... is silly at best for non TP folk .. so, for normally aspirated birds, he who plays with this at altitude is even sillier ..

(d) for most light twins there is no performance left to play with at or about Vmca so the pilot ought not to be anywhere near Vmca in most Types for any normal or routine OEI situation

(e) "Vmca" demonstrations have very little to do with Vmca as such although they provide an exposure to the static Vmca situation

(f) real world Vmca is very much bank angle dependent. Generally it may be assumed that the book figure is based on 5 degree bank (only because the test is not allowed to use more bank ..). If one doesn't use this figure the Vmca goes up .. and, if the bank is allowed to go the wrong way, it goes up rapidly ..

(g) if you must expose the student to the yawing problem .. rather than just discussing it over coffee, then consider arbitrarily introducing a conservative delta by having the instructor restrict rudder travel. A colleague once had to do a lightie endorsement to renew an instrument rating .. the instructor thought it appropriate to have a look at Vmca .. my colleague (who knew lots about Vmca in any case) thought otherwise .. so he restricted rudder travel himself .. confused the instructor greatly ... but got my colleague the tick in the box without exposing himself to fearful risk.

At the end of the day, Vmca is a line in the sand certification boundary condition and has little to do with real world flying .. so, why go there ? .. it's a bit like playing marbles on the middle of a busy road ..

May I relate an example of what you're all talking about?

I had a student who got a little slow on his demonstrated (simulated) asymmetric approach to land. Since it was a competency check I allowed him to do so. It's not every day someone tries to kill me, so I watched with great interest. :}

At about 200 feet he realised he was not on profile, and slow as well. So he added significant power to the live engine. Regrettably, and not unexpectedly, he added only a small amount of rudder, and that after the power increase.

What followed was a textbook approach to Vmc, but he did not recognise it, the aircraft continuing to yaw and roll for long enough for him to know how serious the situation was. (No flaming please - yes I did immediately take over, and no we did not get anywhere near the actual Vmc of the day, although the student's lack of rudder input made it look like we did.)

This student had followed the standard course of training, which included several approaches to a situation resembling Vmca. He was quite current, and primed for the test. He had excellent ground knowledge of Vmca, having discussed the theory & effects in class. Upon encountering unexpected yaw and roll on an asymmetric approach, he froze.

I suspect that he is not alone, and that the relatively few Vmca fatalities have more to do with Lycoming reliability than good training.

(Closing note - in this particular individual's case, his asym approaches are now invariably on or above profile and 5kts above normal approach speed. So he at least has learned something quite valuable.)

Posted separately from the Vmc post...
 

Regarding EF during the take-off roll:

There is one alternative Centaurus - prompt selection of live engine mixture to ICO. That's the instructor's job. Generating the EF at a speed that allows time for the instructor to do this without running off the runway is also the instructor's job.

Better to do this in a simulator as you suggest. But if impossible, an instructor with a hand over the mixtures is at significantly lower risk than one without.

On a similar vein of risk taking, there are many instructors who are perfectly happy to simulate engine failure shortly after take off in a twin by cutting a mixture control (rather than simply retard a throttle). However, when asked would they simulate an engine failure say at 500 ft after take off in a single engine aircraft by cutting the mixture, the answer is generally "you gotta be joking, mate - too dangerous. What if the engine doesn't pick up when you move it back to rich for the go-around?"

Fair enough question, too. Then why risk the same mixture cut in a twin which may also result in the engine not picking up when ready? By the time you realise it hasn't picked up the airspeed will have decayed dangerously with a windmilling prop and with all that drag on one side it the aircraft may not climb and in fact directional control lost if speed is well below blue line.
Morale? Safer option is to use the throttle closure method of simulating an engine failure in a twin - don't you agree?

Why do you say that? How do you know it will be?

There's a Lycoming SB that recommends using mixture whenever possible in order to avoid piston slap, but not below 2000ft.

HFD

I know the original question came from Auz but most of the replies are from the UK

AMC-FCL1.380 includes the JAA ME CRI syllabus. Under the heading Minimum Control Speeds it states:

The purpose of the exercise is to demonstrate that the aircraft is more controllable with the failed engine simulated feathered, and with 5 degrees of bank towards the live engine. in other words to equip the student with sufficient knowledge to be able to deal with the worst case.

The Instructor should fly the aeroplane, whilst the student experiences the differences in rudder force under each condition.

- absolutely not! There is nothing in FCL1 or the UK MEPL syllabus which suggests that this should be a demo.
The stude needs as much hands-on as possible; why do you think they can't fly the sequence I described earlier (18/May)?
Added later:
apologies Whopity, on reflection my comments seem aggressive and that wasn't the intention - it was late :O Splitting the handling is always difficult; I agree that it's useful for the stude to concentrate on the rudder pressures during the teaching of the effect of power and speed during asymm1 but not during the Vmc work in asymm2 because they need to have experience of how the aircraft feels.
HFD

Hugh - you clearly do not understand the purpose of this element of the MEP syllabus. I would strongly suggest that you seek some remedial training before you kill yourself and/or one of your students,

Black gun
 

Does it really matter which country we are training in, is it not the purpose of instructors to train students to be safe and efficent pilots?

I have not done intially twin training for a few years but I used to demonstrate Vmca by locking the rudder at say Vmca +10 and put a lot of emphasis on recognising and recovery.I am now a check and training captain for a large company on turbine engined aircraft and on intial endorsment on type I still do the same.

This is a good diccussion, it is upto us in the industry to discuss with the local CAA, FAA or which ever body we fall under our concerns in order to improve safety.I have heard people say they are not approachable, you will be suprised.

Then why not explain it to us all?

Vmca...ME instruction
 

Gentlemen,

It's been many years since I instructed in light twins...even longer since my initial flight instructor check ride. In turbine equipment, we don't do Vmca demonstrations. (Never saw it in any airline's syllabus.)

However, in the U.S. it used to be required for the checkride for the multi-engine applicant to demonstrate Vmca, as it was also required for the instructor applicant to demonstrate the ability to teach Vmca (both in the classroom and in the airplane). Additionally, for the instuctor applicant, it was also required to demonstrate the knowledge of how not to you kill yourself and the student during such instruction.

The problem is stall speed and Vmca. If Vmca is well above the stall speed, the aircraft will roll before it stalls...and recovery is intuitive and conventional. If the stall speed is well above Vmca, the aircraft will stall before it rolls, and (assuming you have coordinated flight), recovery is, again, a 'normal' stall recovery exercise.

If the two speeds (for the conditons you have at hand) are close to or equal, you will surely spin. In most light twins, this means death to all on board, as spin recovery in light twins is difficult...as John says...better left to the test pilots.

We all know what affects stall speed...what increases it, what decreases it. And, we know what affects Vmca. It's up to the instructor to 'adjust' these variables to ensure the two speeds are not close or equal to eachother. And, all this should be briefed with the student prior to the flight.

In my humble opinion, it is important for the student to know how to handle a Vmca situation...what causes it, what to do to recover...how the aircraft 'feels', etc. This goes along with the demonstration of how Vyse and Vxse vary with weight altitude, bank angle, etc...how Vmca varies with engine power output, CG...et. al. All this is necessary for the student to be 'the master of the aircraft' (as, ultimately, the FAA wants to see on check rides).

Tom

Going back to thread starter, sounded like the aircraft was at such a high altitude it stalled before or at Vmca.
I was taught to demo/practise this at 2000 feet amsl.
Never had any problems with students having a go.
Up to instructor to know how do these manouvres.

Vmca Demonstrations
 

BigEndBob is correct....At that altitude (2000 feet), Vmca should normally be well above the stall speed. Safe, but still effective instruction!!!

Tom

Agreed. If an instructor lets the aircraft spin during a Vmca demonstration (or practise), something went seriously wrong with that instructor's own training.

I remain unconvinced though that the training actually does any good. How many ME pilots would respond well to a real Vmc situation outside the context of a briefed lesson?

O8 :)

Engine failure at Vmca potential killer..its the risk we take...be it small for the greater safety in other areas.

For instance what would happen if one engine failed during power on stall practise...doesn't bare thinking about..but we continue to do power on stalls, even if we recover at stall warn/buffet.

Vmca demonstration practise is useful so that student can apprieciate the rudder loads and technique required to control aircraft at the critical phase between Vmca and blue line, which we practise at altitude.

Hopefully in real situation the student may be able to land ahead and not cartwheel the aircraft across the airfield.

Does any student remember much after training for any emergency, its up to instructors to be inventive on checkouts and go through emergencies rather than just swan about the sky.
Get student/pilot to state the emergency actions before takeoff.

As for engine failure on runways, i've always pulled the mixture, let the aircraft get a bit of forward speed, its easier to keep straight.

BillieBob:
If you bother to refer back to my referenced post on 18/May you will find:
What exactly didn't you like about this?
HFD

MEP EFATO & Take off roll
 

In the UK MEP syllabus we are not required to fail an engine on the take-off roll, only brief it and any EFATO must be done at a minimum of 500 AGL. :D

CY&B

Mustve miss heard him.....Ohh well...........

C Y B - I have a suspicion that that is a company rule - not CAA.

On test (at least on CPL) the candidate is required to DEMONSTRATE a rejected take-off on command (before Vr).

EFATO - usually in the region of 250<300 agl (i.e. before power reduction).

CY&B:
Agreed, but the test includes a "rejected take-off"; some people (not me!) supposedly interpret this as being from an engine failure.

Can anyone explain the purpose of a practice rejected take-off on a test?

HFD

UK CAA MEP RTO & EFATO
 

Just spoke with CFI ohh fountain of all knowledge.......:=

UK CAA MEP RTO not trained or tested, briefed only.

EFATO must be trained and tested above 500 AGL.

CY&B

CY&B:
Would you ask your tame fountain how he/she deals with item 5.1 (RTO) here:
http://www.caa.co.uk/docs/33/FORSRG1157.pdf

I confess that I ask candidates about RTO but don't test, despite it being listed as a mandatory test item. IMHO testing RTO would add cost/risk/stress for no benefit - but I'm willing to be convinced otherwise.

HFD