Newbie Vmca question

[Pilot DAR]

The dangerous area is where Vmc and Stall coincide so that they occur at exactly the same moment.

My totally non patronizing, non sarcastic question is why would that condition be perceived to be dangerous?

Would it not be the case that because you will not be flying below stall speed anyway, having Vmca at the same speed would be as safe as possible?

[englishal]

I assume it is because if you reach Vmc and the aeroplane starts to depart and then you stall at the same time then it could be more likely to lead to a spin? (possibly because now you have two things to deal with...I dunno, rudder inputs could exaserbate the problem and the Vmc corrective rudder during a stall could put you into a spin?). Above stall Vmc will happen and you deal with that, below stall, you will stall before Vmc happens (and hence it won't happen) and you deal with that.

I know of one FI who spun for 6000' before recovery during a Vmc gone wrong demo, I suppose due to the wing nut effect of the engines. Luckily they had 7000' to play with.

[FlyingForFun]

Luckily they had 7000' to play with

However, if he had done the exercise at 2000', he would have reached Vmc at a much higher speed, and never been anywhere near the stall (assuming normally-aspirated). The best (or least bad, for those who don't like doing it) altitude at which to demonstrate Vmc safely is, of course, type-dependant, but higher is not always better. Part of the brief should also be that recovery will be initiated immediately on any indication of approaching the stall - stall warner or light buffet.

I started typing up the benefits of my method, but then stopped because.....

Ok, I'll bite, because the thread doesn't seem to be going away. Reasons for going right down to Vmc include, first of all, experiencing the amount of rudder force that's actually required, especially once the rudder trim runs out. Most students, in the BE76 at least, I've never instructed in any other type so can't comment, will claim to have run out of rudder before they actually have. Getting them to experience the last little push on the pedals might make the difference between a successful EFATO vs a crash (either because of loss of control, or because a perceived lack of rudder has caused them to close the throttles, maintaining control, but resulted in CFIT). Secondly, there's the ability to demonstrate how different techniques affect Vmc, for example wings level vs 5 degrees of bank. By repeating the exercise with different techniques, we can observe the difference in Vmc - but if Vmc is only simulated, this can't be done because it's not possible to stop the rudder travel at exactly the same physical point both times. Thirdly, there's the psychological difference in what a student gains from the exercise. Simulate Vmc, and a student appreciates that he's entered a spiral dive because the instructor won't let him use any more rudder. Demonstrate actual Vmc, and the student realises that there is physically nothing which could be done by either himself or the instructor to rectify the situation except to perform the correct recovery.

I did a straw poll of instructors at my school (it's not a big school, so it was quite a small straw poll!) and none of them had ever heard of Vmc being simulated before - we all, without exception, demonstrate actual Vmc to our students. I need to speak to a CAA staff examiner at some point on a completely unrelated matter, but while I'm there, I'll make a point of asking him what his opinion his.

FFF
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[Big Pistons Forever]

I obviously have strong feelings about the issue of how to best to train for VMC recognition and recovery however this thread now seems exclusively devoted to instructional technique so perhaps it should be moved to the training forum.

I will close with one last thought, and that is I think there is a disconnect between how the rating is taught and how people kill themselves in light twins.

All light twins have negative single engine climb performance at VMC and so if you are close to the ground you simply can not let the airspeed deteriorate below Vyse. Airspeed control to maximize the anemic single engine rate of climb of your typical light twin, is the only way you will survive a low altitude engine failure and IMO is not emphasized enough in ME training.

[27/09]

FlyingForFun

Nothing you have posted justifies repeatedly going to Vmc, at least for some of the aircraft that I fly. The benefits do not outweigh the potential dangers.

Full rudder travel; I agree to a small extent you have a point here. However if the student is on the habit of not knowing that they have full rudder travel it's very likely that in the heat of the momemt, if they were to encounter Vmc, they would not apply full rudder travel anyway. It is much better to have CFIT if that is the outcome than an uncontrolled departure/crash.

Also I would never use the rudder trim in a Vmc demo, you're not going to have time in most Vmc situations to have applied any rudder trim.

Experiencing the effects that differing techniques have on Vmc. Certainly not worth demonstrating in my opinion. The effect of 1/2 ball/5 degrees can be demonstrated very effectively by the effect on rate of climb.

For me psychology doesn't enter the equation. The only thing that matters is that when direction can no longer be maintained with rudder inputs that the correct recovery procedure for loss of control at Vmc is carried out.



Big Pistons Forever

Airspeed control to maximize the anemic single engine rate of climb of your typical light twin, is the only way you will survive a low altitude engine failure and IMO is not emphasized enough in ME training.

Correct, and if the airspeed was managed properly there would be no VMC accidents.

[Pilot DAR]

Full rudder travel; I agree to a small extent you have a point here. However if the student is on the habit of not knowing that they have full rudder travel it's very likely that in the heat of the momemt, if they were to encounter Vmc, they would not apply full rudder travel anyway.

This comment, to me reinforces the need to demonstrate acutal maneuvers. Pilots must be in the habit of instinctively and appropriately using all of the control available to them. That's why the designer put it there! I can recall many times over the years flying, where an abnormal event during the flight required full and held control input. If a pilot is unaware, or reluctant to apply full control as required, that is a problem in itself, letting alone Vmca.

An aspect of this is that with many aircraft, the full deflection of one control will require considerable application of others. The biproduct of all of this control, can be a whole bunch of drag.

So if the pilot is learning the full control available, and the occasion to apply it, the sensation of increased drag resulting, and the need to co-ordinate all of this control, that is a realistic lesson. I cannot be simulated with partial conditions.

It is not making the most of the efforts of certification test flying, if the characteristics which have been shown compliant for a pilot of average skill, attention and strength, if students are not being shown what the aircraft will do. Obviously, there are all kinds of safety mitigations which are wise, certainly including a briefing, but the plane is meant to be flown. If not, it will not pass certification, or could have a caution/warning note in the flight manual if something is marginal.

For pilots who might be flying King Air B200's, are you aware of a special certification condition (23-47-CE5), which describes that the aircraft can reach yaw angles approaching 40 degrees with full pedal deflection? I was required to demonstrate this during test flying for a survey boom installaion. It sounds scary, but was really quite benign. Though I was accompanied by a company pilot (who had not done this either), I had never before flown a King Air. This was no problem, when approached with caution.

I think it unwise to insulate new pilots form these experiences, when they can be demonstrated with safety.

[Big Pistons Forever]

Pilot DAR

Every year in North America there are several smoking holes beside runways caused by light twins which have crashed after loss of an engine and then the subsequent low speed loss of control. I firmly believe that whether or not they would have had a actual VMC demonstration or one where VMC was demonstrated at a higher speed by limiting rudder travel, would have any bearing on the outcome.

These crashes were not caused by not using enough rudder they were invariably caused by failing to maintain airspeed and then when the aircraft started to roll and yaw by failing to reduce power on the operating engine and lowering the nose to maintain airspeed and thus control.


Instructing is not like flying a typical test card, where one facet of the aircrafts' performance is evaluated and care is taken to remove as many variables as possible. Instructional exercises only have value IMO if they are part of holistic continuum of consistent standardized flight profiles, SOP's, pilot decision making points, airmanship, and syllabus that guides the student towards the ability, at any stage of the flight, to understand what the aircraft should be doing and if it isn't; to have the skill and knowledge to recognize this and take appropriate corrective action.

Therefore IMO the primary purpose of the VMC demo should not be to prove that the VMC certification airspeed value is correct or have the student experience the range of rudder travel. Instead IMO the VMC demo should be to demonstrate what happens if a decreasing airspeed trend is not recognized and arrested and the importance of reducing power and lowering the nose at the the first sign of loss of directional control. As I have said earlier this can be just as convincingly done at a higher safer airspeed by limiting rudder travel.

I have wound up monopolizing this thread, which was not my intent and is probably boring most readers of this thread, so how about we agree to disagree on this one

[Pilot DAR]

Indeed, we can agree, and it may not even be to disagree. I'm not attempting to assert that I understand the best practices of flight instruction. I continue to learn, and to do my job better. I always want to understand how the "average" pilot would fly a plane. I want to sort of "average proof" it by design. That is not to say that I am above average, I'm certain that I am below average in some types I fly, I just pick ideal conditions and circumstances, and prepare lots. Hopefully that makes up a bit for some below average skills I might demonstrate.

That said, when I'm evaluating a plane, I'm trying to figure out what the "average" pilot would do if things start happening fast, and to make sure that the plane will perform well enough to meet the minimun standard, and that pilot's expectations.

I simply have not yet formed my opinion as to what training and experience a pilot should be able to go without, and still be adequately compotent.

The Vmca discussion seems particularly relevent, as I completely agree about smoking holes beside runways, and must never make one. I should know better! Thanks for the facinating discussion (but not to truncate it for anyone else!)