Newbie Vmca question

[FlyingKiwi_73]

This aught to be amusing.

Could somebody explain the physics of the rotational force acting on an an aircraft when Vmca is reached.

I was talking with a mate (neither of us are MEP) regarding reducing rudder authority as Vmca approaches with yaw towards the dead engine.

is the Yaw enough to turn the A/C on its back? My answer is yes, my friend argues with full opposite rudder this should not be possible.

Cheers.

[FlyingForFun]

During an asymmetric situation, the main effect of the asymmetry is that it causes yaw towards the failed engine. Rudder is required to counteract that yaw.

At lower airspeeds, there is less airflow over all of the aerodynamic surfaces. This means that all of the aerodynamic controls become less effective. In the case of Vmc (which is subtley different to Vmca, but I think Vmc is what you are actually refering to), the speed has reduced sufficiently that there is not enough rudder authority to counteract all of the yaw that's being created by the asymmetry. The net effect, then, is that even with full oposite rudder applied, there is still some yaw in the direction of the failed engine.

What is the effect of this yaw? Well, what is the effect of any yaw? The end result is no different to if you applied yaw by using the rudder pedals. The yaw will cause roll, the roll will cause more yaw, and so on, and the two will combine to result in a spiral dive, in exactly the same way as applying rudder in any aircraft will result in a spiral dive.

I have demonstrated this to countless students in the 5 years I've been an MEP instructor, and it's never put the aircraft on its back yet! (Mind you, I tend to recover when it gets much beyond about 45 of degrees of bank.....)

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

[FlyingKiwi_73]

so in a way your saying should you let the Spiral dive continue it could end up on its back. However in a dive speed would increase Vmc would <decrease> so some control could be gained?
When Vmc is reached the only way to regain control is to increase speed yes? as in trade height for speed thus- control-??

what is the difference between Vmca and Vmc

[Tinstaafl]

Vmc recovery also involves reducing power on the live side, not just increasing airspeed (nb. you must trade altitude to accelerate), sufficient to regain heading control. Once heading control is regained increasing power can be applied to the live side as it accelerates - typically to at least Vxse or Vyse - to maximise performance.

[AdamFrisch]

Vmc also changes depending on altitude, gear and flaps down, C of G etc.

Funnily enough, Vmc goes down with gears out (as they act as rudders and help stabilize). Vmc also goes down at higher altitude as the engine will lose power.

Vmc is determined during the certification process and is done at sea level, gear and flaps up, fully loaded, aft CG - those are the worst conditions. Anything deviating from this will reduce Vmc and therefore increase your control.

Now, would you want to be close to anywhere Vmc in a real engine out situation? Probably not. I can tell you it's pretty sobering experience seeing how little control one has close to those numbers.

[Whopity]

Vmca is a certification speed; it does not vary with anything; if you change any of the the parameters it is no longer Vmca. As one of the parameters is that its determined at sea level, it is almost impossible to acheive in the air. As with all such speeds you may find differences withinin the definitions of the Certification data. BCAR Section K was the UK certification criteria for light twins prior to JAR23. Essentially it is determined for the take off condition with maximum power on the critical engine, the failed engine windmilling; max AUW and max aft C of G.

Vmc on the other hand is the minimum control speed at what ever conditions its measured under and does vary. It may even be the pilot's personal Vmc when they can no longer maintain straight flight to within 15 degrees.

You can determine a speed at which the aircraft can just maintain directional control however; if the engine were to suddenly fail at that speed, the rate of yaw and roll might well exceed the rate at which recovery action can take place added to which one must consider the delay in reacting.

It should always be rememberd that closing both throttles and lowering the nose immediately solves the asymmetric problem.

[B2N2]

Technically a Vmc demo as performed during a ME check ride or skill test is not how they determine Vmc.
With a Vmc demo we are established SE with the "dead" engine windmilling.
The gradual yaw will lead to roll etc as FFF describes.

The "real" Vmc definition is where both engines are maximum rated power and the critical engine suddenly fails.
If flying below Vmc the very abrupt yaw will cause enough of a rolling moment to turn it upside down.

A Vmc demo will not.

[FlyingForFun]

Funnily enough, Vmc goes down with gears out (as they act as rudders and help stabilize). That might be true if the gear was at the rear of the aircraft, like the rudder is.

However, the main gear is generally very close to the centre of gravity, and will have almost no effect on the stability of the aircraft - at least, not compared to the nose wheel, which is generally well forward of the centre of gravity. Because it is forward of the centre of gravity, it will actually de-stabilise the aircraft in yaw, and increase Vmc.

Counteracting that is the fact that the windmilling prop (remember that Vmca is measured with the prop windmilling) blanks out the gear - the amount of extra drag when the gear is lowered is less than the amount of extra drag when the gear is raised. Difficult to explain without pictures, but there's a good explaination with a picture here (http://westwingsinc.com/Vmca.pdf).

Depending which of these factors overrides the other, Vmc may either increase or decrease when the gear is extended, depending on aircraft type. In any case, the effect will be incredibly small - so much so, it's not even mentioned by many text books.

It should be noted that Vmca is measured with the gear up. This is because it reflects the take-off scenario - if the gear was still down and the speed was low, closing both throttles and landing ahead would probably be the best course of action, terrain permitting. It should also be noted that none of this is at all relevant to the original question!

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

[AdamFrisch]

FFF, that's what I've been told. Gear have a stabilizing effect and will decrease Vmc regardless of where they're placed.

I'm happy to be corrected of course.

[FlyingKiwi_73]

I have also heard that retracting the gear will change the C of G (aft) and could thus cause a problem if you were close to Vmc.

I think i have gleened enough out of the posts above to win my pint.

Looking forward to the Lotto win so i can actually study this stuff for real, for now i'm stuck in SEP land, which seems so much safer the more i learn about twins.

[SNS3Guppy]

Could somebody explain the physics of the rotational force acting on an an aircraft when Vmca is reached.

I was talking with a mate (neither of us are MEP) regarding reducing rudder authority as Vmca approaches with yaw towards the dead engine.

is the Yaw enough to turn the A/C on its back?

The use of terms such as "rotational force" and "yaw" are contradictory in your question, and may lead to confusion.

Can an assymetrical thrust situation in a multi-engine airplane cause a roll, or cause the airplane to roll onto it's back? Yes, easily. Shut down one engine in a light twin, push the other up to takeoff power, then go do stalls. See what happens.

The goal in flying an airplane, of course, is to prevent that from happening. This may be gained in part by increasing airspeed, in part by reducing thrust on the good engine(s) to lessen the assymetrical thust, and in part by the loading and configuration of the aircraft.

In a light piston twin airplane, assymetrical thrust does several things, including producing unequal lift between the left wing and right wing, as well as a yawing force and a rolling force. When insufficient control remains to offset these forces, a roll or control departure can, and generally does result.

[24Carrot]

Never having tried this, I am curious about how fast a light twin can roll right over in this situation. I know "it will depend on..." but are we talking seconds, tens of seconds?

[BackPacker]

I don't know what happens in reality, but in an approved/certified simulator it was all over in less than two seconds. Not just the roll but the crash as well.

Fortunately that one had a reset button.

Of course in a non-moving sim you don't have the seat-of-the-pants feeling of the tremendous yaw that an engine failure would cause, so that may dull your reflexes a bit. On the other hand the yaw also doesn't wipe you off your seat so you can still access all the controls.

[24Carrot]

:eek:And people call helicopters dangerous...

[SNS3Guppy]

Never having tried this, I am curious about how fast a light twin can roll right over in this situation. I know "it will depend on..." but are we talking seconds, tens of seconds?

I had an early King Air 90 that wasn't rigged properly nearly swap ends on me during landing, just by pulling the power to idle. I've had other airplanes in training that don't hardly want to show Vmc characteristics, but that would rather stall first (also a potentially dicey situation).

A multi-engine airplane is not dangerous if flown properly. This is why we teach students about respecting, experiencing, demonstrating, and avoiding the region in which directional control can no longer be maintained. It's not rocket science. It's common sense.

As noted previously, the rationale of retarding power on the good engine needs to be kept firmly in mind for anyone piloting a light twin.

[AdamFrisch]

A question about spins in a twin; would it be more effective to exit the spin by adding power on the inside engine of the spin rather than use the rudder? Has anyone ever tried?

[Tinstaafl]

Twins aren't required to be tested for spin recovery so any recovery technique is likely to be a best guess. Adding power against rotation might stop or slow the spin. Alternatively it could snap it into a spin in the opposite direction or just cause a pitch up, causing the spin to flatten.

[FlyingForFun]

I'm no expert on spins and their aerodynamics, and happy to be corrected on this one (Genghis?). But I believe recovery from a spin in a twin would be difficult whatever method you use, because of the inertia in roll due to the mass of the engines not being on the roll axis like it would be in a single engine aircraft.

As to whether asymmetric power would help you recover.... I'd much rather just keep well clear of the spin altogether in any aircraft not certified for it, but especially in a twin.

Back on the subject of the effect of the gear, and the idea that it moves the C of G rearwards.... on the Beech Duchess, the main wheels retract inwards and won't affect the C of G at all. The nose wheel retracts forwards, so the C of G will be further forward when retracted, not further back. But whichever way the gear retracts, I still maintain that any effect on Vmc would be tiny, and it would be type specific whether Vmc increases or decreases because there are several factors at play which all counteract each other.

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

[FlyingKiwi_73]

With all the variables how do you actually calculate Vmc? its sounds like a moving target, Weight, Gear down/up, Flaps, C of G, Density Altitude! how accurate is the little red line?

[SNS3Guppy]

how accurate is the little red line?

For you, on any given day? It's not. It reflects a demonstrated certification number obtained by the manufacturer. Any change in weight, center of gravity, technique, configuration, air density, propeller efficiency, power setting, aerodynamics, vertical gust (turbulence), etc, will have an impact on that figure.

Vmc as a certification number may be more or less than the speed at which you may find a control departure in your aircraft on any given day, depending on numerous factors.

[moreflaps]

As I understand it, the red line is the airspeed at which the rudder can no longer counter the asymmetric thrust in non accelerating flight. In that sense it would be quite accurate and determined by testing (the test pilot ran out of rudder). Note that the plane should be far from stalling, so it wont immediately spin, but directional control is need to reach a desired landing point ...

As a certificated minimum, it would have been determined in the worst possible loading condition I believe.

Cheers

[Tinstaafl]

No, it won't necessarily be far from stalling. How does 1 kt sound? That's what one light twin has between published Vmc & Vs. And on any particular day Vmc can be anywhere on either side of Vs. Normally aspirated typically have Vmc lower than Vs once they're more than several thousand feet high or have reduced power from maximum, other factors being equal. On the other hand, each degree of bank less than 5 deg towards the live engine is ~3kts increase in Vmc.

Also the criteria for determining Vmc has two, somewhat separate tests: One is more dynamic ie the sudden failure but able to limit heading change to 20 deg or less, and the other steady state to maintain heading afterwards. They're allowed use up to 150lb force applied to the pedal, and even after trimming you can be left with 20 lb residual. It's rare in normal flight to ever apply 150lb force with your foot, let alone be called upon to do it without warning - which would be the case for an unexpected Vmc departure.

A Vmc recovery, as usually taught, is more akin to the steady state situation.

The important thing to note is that reducing power on the good engine is an important part of the recovery, not just regaining speed. Unfortunately, at low heights the time & spaces to effect a recovery is limited *and* the pilot has to go against the desire to maintain max. available power to avoid a forced landing. In a light twin, a forced landing is often inevitable, just like in a single. Doing so under control almost invariably has a far better outcome than attempting to continue flight until a Vmc departure has you turn turtle & cartwheel in.

Vmc is a place to be avoided, but just as importantly, so is Vs when asymmetric.

[SNS3Guppy]

Banking into the good engine isn't done on transport category aircraft; engine-out situations are handled with the wings level (specifically line operations, as opposed to certification). Vmc numbers aren't published for all aircraft, either.

In light aircraft, Vmc can be greater or lesser than the red radial line. It should be thought of as a general reference or reminder, but nothing more. On a colder day than the day certification was performed, the engine will produce more power, and loss of directional control will occur at a higher value than the red radial line. One must also take into account the fact that discrepancies in airspeed indication, pitot placement, local airflow, lag, and other factors mean that your airplane here, today, isn't necessary displaying exactly what Joe Schimoley's airplane did 30 years ago during certification trials.

Many airplanes, unless trimmed out, can leave your leg shaking and quivering after some time doing single engine work, or engine-out work. Especially after a lengthy session. On some airplanes, it's not uncommon to need 75 lbs of force to press the rudder or hold full rudder. On some airplanes, it may require that to hold the rudder with all engines working, if using full rudder deflections. When training with lots of power changes and not much opportunity to retrim, it can be a real work-out.

Playing around near the published Vmc numbers is a bad idea. One can alleviate a lot of one's work load, including the shaking syndrome and the need to feel like banking into the other engine, by carrying more airspeed. More airspeed means less bank needed, less rudder needed, and an easier job of flying the airplane.

If you do find yourself slipping down toward the evil rad radial line, remember that it represents a solitary theoretical number from long ago, and has nothing at all to do with when you'll lose control on a given day.

[FlyingForFun]

Please, let's be clear on the difference between Vmc, and Vmca. The two are becoming confused.

Vmca is shown on the ASI by a red line. It is determined by a test pilot, under very specific circumstances. It represents a speed at which, if an engine suddenly fails, the test pilot was able to recover with a heading change of no more than 20 degrees.

Vmc can, and does, vary. Therefore, it can't be published. It may be higher or lower than Vmca, and it may be higher or lower than stall speed. (Incidentally, stall speed will be lower than the published Vs, because Vs is published at idle power, and stall speed will decrease with power, even if that power only comes from one engine.) Vmc is determined by gradually slowing the aircraft down until you reach such a speed that you can't maintain control.... that is very different from Vmca in a number of respects.

Tinstaafl, where do you get your figure of 3kt per degree of bank? My school teaches recovery with wings level, but I demonstrate Vmc to students with wings level and with 5 degrees of bank, and demonstrate that it makes a difference of about 2kt to Vmca. (In fact, I don't bother doing the demo unless it's a smooth day, because the difference is so small you can't see it in bumpy weather... although it's covered in groundschool instead.)

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

[SNS3Guppy]

Actually, you'll find that Vmc and Vmca are used interchangably.

[FlyingForFun]

Yes, SNS3Guppy, they are used interchangeabley, but they shouldn't be.

You said:how accurate is the little red line?For you, on any given day? It's not. It reflects a demonstrated certification number obtained by the manufacturer. Any change in weight, center of gravity, technique, configuration, air density, propeller efficiency, power setting, aerodynamics, vertical gust (turbulence), etc, will have an impact on that figure.Vmc - the value which changes changes depending on weight, centre of gravity, etc etc etc, is generally measured and demonstrated by first failing an engine at a safe speed, then gradually slowing down.

In contrast, red line speed, Vmca, is measure by first flying at the given speed, then seeing whether control can be maintained when a sudden engine failure occurs.

By using the two interchangeably, this important difference is being overlooked (or at least might well be overlooked by someone reading this thread who doesn't know better), which might lead someone to expect an aeroplane to be capable of doing something which it can't.

(It is very important, when talking about any speed, that we are very clear which speed it is that we are talking about. We don't use Vne, Vno and Va interchangeably because they both happen to be related to the high-speed limits of the aircraft. If we did, it would cause confusion. And so we also shouldn't use Vmc and Vmca interchangeably either, because that too will cause confusion.)

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

[SNS3Guppy]

Yes, SNS3Guppy, they are used interchangeabley, but they shouldn't be.

Of course they should. Vmc is the point at which directional control is lost with the critical engine suddenly made inoperative; Vmca is that point in the air, and Vmcg is that point on the ground.

(It is very important, when talking about any speed, that we are very clear which speed it is that we are talking about. We don't use Vne, Vno and Va interchangeably because they both happen to be related to the high-speed limits of the aircraft. If we did, it would cause confusion. And so we also shouldn't use Vmc and Vmca interchangeably either, because that too will cause confusion.)

Apples and oranges, when you speak of Vmc vs. Vmca, and confusing speeds with no relation to one another such as Vno, Va, and Vne.

Vmc and Vmca are the same. Vno, Va, and Vne are not.

Vmc means minimum control speed with the critical engine inoperative. Period.

The certification standard for most light twins, or at least those produced in the United States, is 14 CFR Part 23. The definitions for Part 23 are found in Part 1, and the definition provided therein for Vmc is quite simply "VMC means minimum control speed with the critical engine inoperative."

Provision of this information in the aircraft flight manual is a requirement of the certification regulation 14 CFR 23.1583, as noted:

§ 23.1583 Operating limitations.
The Airplane Flight Manual must contain operating limitations determined under this part 23, including the following -
(a) Airspeed limitations. The following information must be furnished:
(1) Information necessary for the marking of the airspeed limits on the indicator as required in § 23.1545, and the significance of each of those limits and of the color coding used on the indicator.
(2) The speeds VMC, VO, VLE, and VLO, if established, and their significance.


Pick up a dozen aircraft flight manuals for various light twins, and you'll find the terminology used interchangeably; some manufacturers will refer to the red line as Vmc, others to it as Vmca, and in some cases, you'll find it used interchangeably in the same aircraft flight manual or pilot operating handbook.

The FAA uses it interchangeably throughout it's literature, because Vmca is Vmc. Vmc is defined as an airborne speed by the use of Vmca, and as a ground speed by Vmcg.

The certification regulation spelling out the establishment of Vmc is 14 CFR 23.149:

§ 23.149 Minimum control speed.
(a) VMC is the calibrated airspeed at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane with that engine still inoperative, and thereafter maintain straight flight at the same speed with an angle of bank of not more than 5 degrees. The method used to simulate critical engine failure must represent the most critical mode of powerplant failure expected in service with respect to controllability.
(b) VMC for takeoff must not exceed 1.2 VS1, where VS1 is determined at the maximum takeoff weight. VMC must be determined with the most unfavorable weight and center of gravity position and with the airplane airborne and the ground effect negligible, for the takeoff configuration(s) with -
(1) Maximum available takeoff power initially on each engine;
(2) The airplane trimmed for takeoff;
(3) Flaps in the takeoff position(s);
(4) Landing gear retracted; and
(5) All propeller controls in the recommended takeoff position throughout.
(c) For all airplanes except reciprocating engine powered airplanes of 6,000 pounds or less maximum weight, the conditions of paragraph (a) of this section must also be met for the landing configuration with -
(1) Maximum available takeoff power initially on each engine;
(2) The airplane trimmed for an approach, with all engines operating, at VREF, at an approach gradient equal to the steepest used in the landing distance demonstration of § 23.75;
(3) Flaps in the landing position;
(4) Landing gear extended; and
(5) All propeller controls in the position recommended for approach with all engines operating.
(d) A minimum speed to intentionally render the critical engine inoperative must be established and designated as the safe, intentional, one engine inoperative speed, VSSE.
(e) At VMC, the rudder pedal force required to maintain control must not exceed 150 pounds and it must not be necessary to reduce power of the operative engine(s). During the maneuver, the airplane must not assume any dangerous attitude and it must be possible to prevent a heading change of more than 20 degrees.
(f) At the option of the applicant, to comply with the requirements of § 23.51(c)(1), VMCG may be determined. VMCG is the minimum control speed on the ground, and is the calibrated airspeed during the takeoff run at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane using the rudder control alone (without the use of nosewheel steering), as limited by 150 pounds of force, and using the lateral control to the extent of keeping the wings level to enable the takeoff to be safely continued. In the determination of VMCG, assuming that the path of the airplane accelerating with all engines operating is along the centerline of the runway, its path from the point at which the critical engine is made inoperative to the point at which recovery to a direction parallel to the centerline is completed may not deviate more than 30 feet laterally from the centerline at any point. VMCG must be established with -
(1) The airplane in each takeoff configuration or, at the option of the applicant, in the most critical takeoff configuration;
(2) Maximum available takeoff power on the operating engines;
(3) The most unfavorable center of gravity;
4) The airplane trimmed for takeoff; and
(5) The most unfavorable weight in the range of takeoff weights.

Let's not forget Vmcl, which is the minimum control speed in landing configuration. Then there's Vmcl-2, which is applicable to aircraft with three or more engines (before anyone gets uppity about this being a light airplane forum, let's nor forget that there are indeed light airplanes with three or more engines; the Trilander springs to mind). Clearly it's not quite as simple as you might think.

Vmc is the basic definition, and simply means the speed at which directional control can no longer be maintained. It's specified, or clarified to the phase of operation by the addition of letters. In the case of the topic under discussion Vmca, to signify the minimum control speed while airborne.

Lest we simply read Part 23 and let it drop, let's keep in mind that not only do various manufacturers interchangeably use Vmc and Vmca, but so does the FAA throughout it's various publications. In fact, in some handbooks, such as the Pilots Handbook of Aeronautical Knowledge, Vmca is used, rather than Vmc. In Appendix A of Part 60, dealing with certification of simulators, for example, the FAA only refers to Vmca. In Appendix F, providing definitions, we find the following:

Vmc Minimum Control Speed.
Vmca Minimum Control Speed in the air.
Vmcg Minimum Control Speed on the ground.
Vmcl Minimum Control Speed--Landing.

In FAA H-8083-3A, the Airplane Flying Handbook, Vr is defined as:

• VR — Speed at which the rotation of the airplane is initiated to takeoff attitude. This speed cannot be less than V1 or less than 1.05 x VMCA (minimum control speed in the air). On a single-engine takeoff, it must also allow for the acceleration to V2 at the 35-foot height at the end of the runway.

FAA H-8083-25a, the Pilots Handbook of Aeronautical Knowledge (under Chapter 10, Aircraft Performance), we find the terms defined as:

• VMCG—minimum control speed on the ground, with one engine inoperative, (critical engine on two-engine airplanes) takeoff power on other engine(s), using aerodynamic controls only for directional control (must be less than V1).
• VMCA—minimum control speed in the air, with one engine inoperative, (critical engine on two-engine aircraft) operating engine(s) at takeoff power, maximum of 5° bank into the good engine(s).

Advisory Circular AC25-7A, a flight test guide for certification, states:

(1) General.
(i) Prior to beginning the minimum control speed tests, an evaluation should be conducted to determine which engine's failure will result in the largest asymmetric yawing moment (i.e., the "critical" engine). This is typically done by setting one outboard engine to maximum thrust, setting the corresponding opposite engine at idle, and decelerating with wings level until full rudder is required. By alternating power on/power off from left to right, the critical engine can be defined as the idle engine that requires the highest minimum speed to maintain a constant heading with full rudder deflection.
(ii) For propeller-driven airplanes. VMCA, VMCG, and VMCL (and VMCL-2, as applicable) should be determined by rendering the critical engine(s) inoperative and allowing the propeller to attain the position it automatically assumes. However, for some engine/propeller installations, a more critical drag condition could be produced as the result of a failure mode that results in a partial power condition that does not actuate the automatic propeller drag reduction system (e.g., autofeather system). One example is a turbopropeller installation that can have a fuel control failure, which causes the engine to go to flight idle, resulting in a higher asymmetric yawing moment than would result from an inoperative engine. In such cases, the minimum control speed tests must be conducted using the most critical failure mode. For propeller-driven airplanes where VMCA is based on operation of a propeller drag reduction system, VMCA should also be defined with the critical engine at idle to address the training situation where engine failure is simulated by retarding the critical engine to idle. If VMCA at idle is more than one knot greater than for the engine failure with an operating drag reduction system, the idle engine VMCA should be included in the Normal Procedures section of the Airplane Flight Manual (AFM) as advisory information to maintain the level of safety in the aforementioned training situation.
(iii) Airplane Flight Manual values of VMCA, VMCG, and VMCL (and VMCL-2, as applicable) should be based on the maximum net thrust reasonably expected for a production engine. These speeds should not be based on specification thrust, since this value represents the minimum thrust guaranteed by the engine manufacturer, and the resulting minimum control speeds will not be representative of what could be achieved in operation. The maximum thrust used for scheduled AFM minimum control speeds should represent the high side of the tolerance band, but may be determined by analysis instead of tests.
(iv) When determining VMCA, VMCL, and VMCL-2, consideration should be given to the adverse effect of maximum approved lateral fuel imbalance on lateral control availability. This is especially of concern if tests or analysis show that the lateral control available is the determining factor of a particular VMC.

Note this last sentence, "of a particular Vmc." There is more than one Vmc; various terms are used to cllarify Vmc. Vmc means only the speed at which directional control is lost. It doesn't define which speed is to be used, hence the application of Vmca, Vmcg, and Vmcl (and of course, Vmcl-2).

Vmca is Vmc. Vmcg is Vmc. Vmcl is Vmc. Vmcl-2 is Vmc.

The terms may be used interchangeably, except that when the terminology "Vmc" is given, it doesn't specifically state whether in flight or on the ground, or reference the configuration or circumstances under which control is expected to be lost. It is,however, used frequently by the governing bodies, certification authorities, manufacturers, and test facilities and personnel, in an interchangeable basis with Vmca.

[FlyingForFun]

Wow - someone's very bored to have found that many quotes!

I wasn't aware that the FAA use the term Vmc so loosely, and I stand corrected. I don't have anything from the CAA to quote back at you (I'm not bored enough!), but certainly from the point of view of the training which is given as part of the MEP rating, and the associated written exam, Vmc has a more definite meaning on this side of the pond - which is why it's always bothered me when people use the term "incorrectly".

However, I don't think my Vne, Vno, Va comparison was apples and oranges at all. Let's say we invent a phrase, "Vmax", which we use interchangeably to mean either Vne, Vno, Va, or any other maximum speed under a given set of circumstances. In other words, there would be more than one Vmax. It would be very confusing, wouldn't it? Well, isn't the FAA use of Vmc, just as confusing? Because it can apply to many different speeds - you say yourself that there is more than one Vmc - and it needs additional clarification as to exactly which speed it refers to each time it's used.

Anyway, thanks for the informative quotes. I will bear in mind the FAA's loose definition of Vmc in future!

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

[FlyingForFun]

(Quick aside... I've found my debate with SNS3Guppy really interesting, but I do feel we owe an apology to FlyingKiwi for hijacking his thread. The discussion has gone way beyond the scope of the original question!

And it's so refreshing to have a good debate on PPRuNe without it turning personal in any way!)

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

[Tinstaafl]

Dammit, FFF, you.....you......you bloody apologist, you! So take that!






Oh, the approx. 3 knots / degree I saw used in various USA based reference texts & online but can't remember where. It's only approximate so your 2 kts /degree could well be more accurate in the type you fly. It could also be related to situation ie static vs dynamic heading control.

Vmc vs Vmca et. al.: The FAA in its 'Airplane Flying Handbook' makes it clear that Vmc can vary and also that the published Vmc is under a particular set of conditions. Generally I think context provides enough distinction as to whether one is referring to the published or 'at the moment' Vmc. Published Vmc is only a guide because unless every certification criteria is met then it is unlikely to be correct for the moment. I tend to use Vmca/Vmcg to distinguish between themselves if there is likely to be confusion about which one I mean.

[FlyingForFun]

Tinstaafl,

I know when I've been beaten! (Or, to put it another way, we're never experienced enough to not be able to learn something new.)

As for my 2kt, though, I meant 2kt altogether, not 2kt per degree. Typically, I might find that Vmc (the static one, decreasing speed gradually, with the particular conditions of the day) would be 70kt with no bank, and 68kt with 5 degrees of bank. That's considerably different to whatever you read! Yes, dynamic vs static could explain the difference... although your misunderstanding of my earlier post means that the difference is considerably more than I think you thought I was saying.

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

[SNS3Guppy]

I will bear in mind the FAA's loose definition of Vmc in future!

It's not a "loose definition." It's quite precise.

Vmc means the speed at which directional control can no longer be maintained, period.

What Vmc doesn't tell you is when and where.

What Vmc does not do is give you specifics. Vmc in the air is not the same as Vmc on the ground. Vmc in the air under the conditions predicated for Vmca is not the same as Vmc while configured for landing, Vmcl (or Vmcl-2, as applicable).

To assign the red radial line on the airplane as Vmc is correct, because that's the published speed at which directional control may be anticipated to be no longer available under the prescribed certification conditions for air operations. Vmcg is not shown on airspeed indicators, nor is Vmcl. therefore, the red line is Vmc, one of several Vmc's but it is specifically Vmca. To refer to it as either one is correct, because this is a correct definition. Not a "loose" one. Vmc on the airspeed indicator is the published certification number at which directional control can no longer be maintained within 20 degrees when the critical engine is suddenly retarded, the good engine maintained at takeoff power, an aft center of gravity with the least favorable weight, in the takeoff configuration. This is certification Vmc, and as it's an airborne number in the takeoff configuration, it is also Vmca; the terms are synonymous for this application.

The same cannot be said of the red radial line and Vmcg, Vmcl, or Vmcl-2. Those numbers are not the same as Vmca (although they are Vmc numbers). Accordingly, whereas we know that the red radial line speaks to specific conditions of establishment, we know that this particular Vmc value is only an airborne, takeoff-configuration number. It is Vmca, but it a Vmc value none the less. To refer to any of the Vmc values as Vmc is correct, but to refer to them in context is more correct, or more precisely, more precise. That is, while Vmca, Vmcg, Vmcl, and Vmcl-2 are all Vmc, a more exact rendering of "Vmc" when referring to these speeds appends the letter or letters which speak to the circumstances under which the speed is derived.

It is not correct to say that Vmc is the red radial line, but that Vmca is the actual speed at which control will be lost. Neither is it correct to say that Vmca is the red radial line, and Vmc is the actual speed at which control will be lost. Vmca is Vmc. Vmc is Vmca. Vmca is Vmc in the air. Vmc in the air is Vmca. This isn't a loose definition; it's a regulatory one, a design and standards one, and one spelled out throughout technical manuals, handbooks, manufacturer publications, certification standards, and so forth. It's not the definition which is loose in this case, but perhaps your understanding of the subject. I realize that you may have been taught differently in class, but that doesn't change the fact.

As Tinstaafl noted, whether one chooses to refer to the red radial line (or published numbers) as Vmc or Vmca makes no matter. It's a general guideline. The actual airspeed under which control might be no longer possible to maintain will vary with aircraft loading, configuration, ambient conditions, center of gravity, and so forth. The actual Vmc (or Vmca, if you will) varies, and can be lesser or greater than published.

[FlyingForFun]

SNS3Guppy,

Given the points you made by your earlier quotes, I'd agree with almost everything you said in your last post.

I think the only thing we're now disagreeing on is whether Vmc is a "loose definition". This might be subjective, and I think we'll have to agree to disagree, because despite agreeing with what you're saying, I still think that it's fair to call any definition which can have a number of different meanings "loose". I don't expect you to agree with me on that, it's just my opinion.

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

[SNS3Guppy]

You're doubtless familiar with the story of the man who bought two horses named Arnie and Sam, and took them back to his farm. One was a rider, the other a breeder. He tried to work them for several days, but in the end he took them back to the seller.

"What seems to be the problem?" asked the seller.

"It's quite simple," said the farmer. "I can't tell them apart. I never know which to call, and it's got me in a jam."

The seller looked the horses over and then said "Come back tomorrow. Let me think on this for a while. You can pick them up in the morning."

In the morning the farmer returned, and the seller handed him the lead ropes to the horses. "I figured it out." He said.

"Really?" asked the farmer. "That's great. How do I tell them apart?"

"Well," said the farmer, pointing to the crown at the top of the mane of the horse on the left, "if you look real close, you'll see that the black one is about an inch taller than the white one."

I understand where you're coming from, but I think it's more that you either disbelieve the concept here, or don't understand it.

Both horses are just that. Horses. Vmc and Vmca are both minimum control speeds (or the speeds at which directional control can no longer be maintained). One horse is a breeder, one horse a rider. Both horses are capable of breeding, but one is specifically for riding. Vmc and Vmca are both minimum control speeds, but only one specifically points to minimum control speed in the air. That's Vmca.

We could have many horses in a herd. We could have an Arabian, a Quarterhorse, an Appaloosa, and a Lipizzan. All are horses. The Arab is good for mountain and endurance riding. The Quarterhorse is good for cutting cattle and roping. The Appaloosa is excellent for western riding disciplines, and the Lipizzan for show. Each one a horse, one would not be remiss in calling any of them horses, for horses they are. To define each of them as a horse would be quite correct.

If one were to select the Arab for a trail ride, one would refer to the horse as a "horse" or an "Arab" interchangeably, because the horse is both. One could not refer to the Arab as a Lippizan, or the Quarterhorse as an Appaloosa, because they are not the same thing, even though they are each horses. To refer to any of them as a horse is not a loose definition; it's exactly what they are. To refer to any of them by their proper breed name is also not inexact or incorrect, because they are exactly that breed. To refer to any of the breeds by the proper breed name, or to refer to them as a horse, interchangeably, does not a loose definition make, because both are fully correct, and both describe the animal well.

Likewise, Vmca, Vmcg, Vmcl, and Vmcl-2 are all versions of Vmc. One can refer to any of them as either Vmc, or by their specific name. Therefore, Vmca is very much Vmc. Likewise, Vmcg is very much Vmc. Vmcl is very much Vmc. Vmcl-2 is very much Vmc.

Horse is a generic name for the type of animal. Arab, Quarterhorse, Appaloosa, or Lippizan are all horses, but are unique in their applications and strengths. An arab is a horse. A horse that's an Arab may be referred to as a horse, or as an Arab.

Vmc is a generic name for a situation in which directional control can no longer be maintained. Vmca, Vmcg, Vmcl, and Vmcl-2 are all Vmc scenarios, but are unique in their aplications and criteria. Vmca is Vmc. Vmc that's in the air may be referred to as Vmc, or as Vmca.

The terms, each exactly correct, may be used interchangeably, and neither are "loose." Vmc means directional control, and if we're talking about the red radial marking on the airplane, it's a given that it's Vmca, because that's the only Vmc marking required on the airspeed indicator. Vmcg, Vmcl, and Vmcl-2 are not required on the airspeed indicator. When establishing the minimum control certification number and instrument marking,then, we can correctly say we're establishing Vmc, because it's the only one that's going to be put on the indicator. If we're establishing something else, we'll note as much by being specific by saying it's the ground minimum control speed, Vmcg, for example. We know that Vmca is the red radial line because only the airborne takeoff configuration Vmc applies as marked on the airspeed indicator. We can say it or simply know it, but it's still Vmc, and it's still Vmca.

Vmc, of course, defining the speed at which we lose directional control, or specifically, at which directional control can no longer be maintained, varies as previously described. The published number is a reference only, and one should never assume that it reflects real-world conditions, except in approximation. You could correctly say, then, that Vmc as published, and Vmc as experienced in flight, are different.

Put another way, we're all familiar with Vx and Vy. While these numbers are known and published, they change with altitude, and they also change with ambient conditions. Vx and Vy are predicated on power, and where more power is available, the numbers are different than published. Many people disregard the difference or don't know how to figure it, but that usually won't hurt someone. Disregarding Vmc will. Therefore, while it's okay to fly the published numbers for Vx and Vy and be "close enough," it's not okay to assume the published numbers for Vmc are close enough; directional control may be lost before or after that published number. Vmc published and Vmc actual are different animals. For a worse-case scenario, it's Vmca that interests us: low, slow, and high power setting is what will bite us, as on a takeoff or go-around. It's Vmc, very much Vmc, but it's the Vmca (of all the Vmc's) that generally interests us the most.

The published number may correctly be called Vmca because it is Vmca. It may be correctly called Vmc because it is Vmca. The published number Vmc is always the Vmca number, whether we call it that or not, but it's very appropriate to use the terms interchangeably, because they are. Nothing loose about it. I harp on this point because as you said previously, we shoudn't be ambiguous about our terminology when discussing airspeeds. It was you who said we shouldn't confuse them, and you're right. Hence the lengthy clarification.

[FlyingForFun]

I thought this might have come to an end when I agreed to disagree, but ok, let's continue!You're doubtless familiar with the story of the man who bought two horses named Arnie and Sam, and took them back to his farmI wasn't, but I am now. It's a good analagy - and it makes my point very well.

If I wanted to buy a show-horse, I would go to the horse dealer and ask if I could buy a Lipizzan. I'd then get what I wanted. If I simply asked him for a horse, I'd quite likely come away with the wrong type of horse - unless he sought further clarification. The word "horse" works perfectly well in many circumstances, but is too ambiguous to be of any use when I'm at the horse dealer telling him what I want to buy.

"Vmc" is exactly the same as "horse". It is often perfectly acceptable to use it, either because it doesn't matter exactly what Vmc we are talking about (rare), or because the context provides clarification (more common). But it can also be ambiguous.

Let me ask you some questions:

a) What happens to the control of the aircraft at Vmc?
b) Can you explain why Vmc is lower when 5 degrees of bank towards the live engine is used compared to when the wings are level
c) Does Vmc change with height?

In question a, it doesn't matter which Vmc we are talking about, because the answer is the same regardless: the answer is that control is lost.

In question b, the context tells us that we can't be refering to Vmca, we must be talking about the actual speed at which control is lost. If we were talking about Vmca, the question would be nonsense because Vmca is defined as not being wings level, but the question asks about Vmc with wings level and implies that Vmc exists, and is different, if wings are level.

In both of these cases, the phrase "Vmc" is absolutely adequate.

But in question c, it is not. The answer to the question depends on what Vmc we are talking about. If we were being asked about Vmca, we might answer "No, Vmca is always quoted for sea level". If we were being asked about the actual speed where control is lost, we might answer "Yes, Vmc decreases with height in an aircraft with normally-aspirated engines because the good engine produces less power the higher it is."

So, in the case of question c, the phrase "Vmc" is ambiguous.I think it's more that you either disbelieve the concept here, or don't understand it. I believe the concept thanks to your quotes, and I understand it perfectly. Just because what you are saying is factually correct, that doesn't mean I have to think it's a good idea!

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

[SNS3Guppy]

I thought this might have come to an end when I agreed to disagree, but ok, let's continue!

I don't do that (agreeing to disagree). It simply signals a popcorn break.

Let me ask you some questions:

a) What happens to the control of the aircraft at Vmc?

In question a, it doesn't matter which Vmc we are talking about, because the answer is the same regardless: the answer is that control is lost.

Well, not really. It's the point at which control can no longer be maintained, as defined by a 20 degree change in heading. A loss of control is a different matter entirely. That might sound like semantics, but it's not.

b) Can you explain why Vmc is lower when 5 degrees of bank towards the live engine is used compared to when the wings are level

In question b, the context tells us that we can't be refering to Vmca, we must be talking about the actual speed at which control is lost. If we were talking about Vmca, the question would be nonsense because Vmca is defined as not being wings level, but the question asks about Vmc with wings level and implies that Vmc exists, and is different, if wings are level.

Sure we're referring to Vmca. I don't think you understand what Vmca is, yet.

You still seem to think it represents something other than what it does. Rather than explain it again (I think it's been very thoroughly covered thus far, insofar as the terminology goes), read again.

Where do you find Vmca defined as wings not level? Vmc is Vmca. Vmca is Vmc. Vmca is Vmc in the air. Remember?

As to your question, the five degree bank isn't used with all aircraft. When you move up to transport category aircraft, for example, you'll find that wings-level is the order of the day when addressing an engine-out, in most cases.

In both of these cases, the phrase "Vmc" is absolutely adequate.

It's adequate insofar as the fact that directional control can no longer be maintained. In the context of the red radial line with reference to Vmc or Vmca, specific conditions are imbued and inferred. With respect to the actual point at which directional control can no longer be maintained (nearly always something other than the little red radial line, both Vmc and Vmca directly adress that speed. It's the point at which directional control can no longer be maintained, in the air.

Vmc, of course, can also refer to the same thing on the ground, which is Vmcg, or in approach configuration, which is Vmcl, or Vmcl-2.

c) Does Vmc change with height?

But in question c, it is not. The answer to the question depends on what Vmc we are talking about. If we were being asked about Vmca, we might answer "No, Vmca is always quoted for sea level". If we were being asked about the actual speed where control is lost, we might answer "Yes, Vmc decreases with height in an aircraft with normally-aspirated engines because the good engine produces less power the higher it is."

So, in the case of question c, the phrase "Vmc" is ambiguous.

Perhaps you mean to ask if it changes with altitude, and with most light airplanes, yes, it does. Vmc is Vmca, and Vmc and Vmca change with altitude, though in most cases the published numbers do not, nor does the red radial line move.

For certification purposes, the number tends to remain fixed, but the relationship to actual directional control varies with the aircraft and powerplant system in use. It's fair to say that EAS and TAS for Vmc changes with altitude, though you may or may not see an actual change in the indicated airspeed at which directional control can no longer be maintained. You haven't provided enough information.

Where Vmc, meaning the ability to no longer maintain directional control, changes with altitude, the term is not at all ambiguous, because it means just what it says: the ability to no longer maintain directional control.

The numbers may be different, but the term is still valid and precise.

Re-read again. You're missing something. Can you figure out what it is?

You may have to have the conversation alone for a few days. Time to go fly.

[Pilot DAR]

The departure of one person from the thread, does not mean another poster is having a conversation alone....

[FlyingForFun]

I get the feeling you are arguing for the sake of arguing now.

- We agree that Vmc can have many different values.
- It's clear that you don't have a problem with this.
- For my part, I accept that this is true - I have stated that I don't like it, but there's nothing I can do about it.
- In all other respects, we seem to agree.

As far as I'm concerned, there's nothing else to discuss. I've found this conversation useful and enlightening - I will no longer assume, when I hear people use the term Vmc, that it's being used to describe minimum control speed in any particular circumstances as I used to, but will seek clarification if required. And I'll give clarification where required when I use the term Vmc myself.

You also said I don't understand what Vmca means. It's a pity you can't concisely correct my misunderstanding, rather than referring me back to the same posts that I had misunderstood earlier. Generally, when someone misunderstands something I say, I try to re-word it to help them understand.

However, I re-read much of what you've written, and I think you may also be suggesting that Vmca can have many values, that it doesn't only refer to the certification criteria used to work out the red-line value but that it can also be used to refer to actual in-flight values. Is that what you mean? If so, then I will take everything I've just said about Vmc and apply it to Vmca too.

If you feel I've still misunderstood something, then I look forward to being further enlightened when you return from flying. If you want to disagree with my opinion then that's fine, but I can't see any point in debating further something on which I know we disagree.

FFF
----------

[FlyingKiwi_73]

(Quick aside... I've found my debate with SNS3Guppy really interesting, but I do feel we owe an apology to FlyingKiwi for hijacking his thread. The discussion has gone way beyond the scope of the original question!

And it's so refreshing to have a good debate on PPRuNe without it turning personal in any way!)



No problem FFF, i have won my beer with said mate and learnt allot, i have also been put off flying twins for life!

Thanks all

[Pilot DAR]

Without wanting to spark a whole new debate, I will offer the following photo for an example. I took this in stable flight, during flight testing in a Navajo last week. I was applying full rudder to maintain control.

Though hard to see, the indicated airspeed is 10 MPH less than the red line, and the aircraft is banked to the right, slightly climbing in a left turn. The stall warning was sounding while I did this.

To be fair to Vmc(whichever - I'm not trying to incite an argument here), the prop is feathered, and not windmilling, and it was at altitude. Maximum power was applied on the right engine. This is becasue I was checking the general handling, and stalls, with light aft C of G. Vmc(whichever). I did stall the aircraft in this configuation, with no unusual outcome. I will be determining if the actual speed of Vmc was affected by the modification next week, with the prop windmilling.

http://i381.photobucket.com/albums/oo252/PilotDAR/Jims%20DAR%20Testing/IMG_2367.jpg

[FlyingForFun]

No new debates there, DAR. I think we're all agreed that's perfectly possible. Thanks for the proof though! The debate is purely about the terminology we'd use to describe it (or the terminology we'd use to describe the speed a couple of knots lower where you wouldn't be able to maintain control.)

Out of interest... you said the stall warner was going - but how close to the stall were you actually required to get to complete your test flight profile? Asymmetric flight near the stall is something I have little experience of, and little desire to practice!

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

PS - Thanks for your PM - reply coming later!

[Pilot DAR]

the stall warner was going - but how close to the stall were you actually required to get to complete your test flight profile?

FFF,

Yes, the stall warning was sounding during this element of my flight. it had started at 75 MPH IAS. I observed 73 MPH IAS while maintaining control with the left engine feathered, and right at MCP (flaps and gear up). With some reduction to the right power to maintain straight flight, I was able to fly as slowly as 67 MPH IAS, at which point pitch control could not be maintained. The first indication of the inability to control pitch, is my indication of a stall. In this case, the Navajo gently dropped the nose, but did not change attitude in roll or yaw.

I am not saying that some aircraft may not display alarming tendancies in this configuration, this aircraft did not. I was flying by myself, in the best possible conditions, with lots of altitude, no rush, and no pressure [to go around, or otherwise deal with an emergency].

This flying was accomplished in accordance with a Transport Canada approved flight test program, with many safety measures in effect. Pilots should not be "experimenting" in this phase of flight.

[SNS3Guppy]

You also said I don't understand what Vmca means. It's a pity you can't concisely correct my misunderstanding, rather than referring me back to the same posts that I had misunderstood earlier. Generally, when someone misunderstands something I say, I try to re-word it to help them understand.

I tend to speak for myself, not for you. Perhaps you shall do the same. What I should or shouldn't do insofar as what you might say is entirely irrelevant, so long as I'm making my own posts. When you begin making my posts, by all means go ahead and determine what should be in them. Repeating material which has been presented several times isn't necessary and won't be happening.

i have also been put off flying twins for life!

Why would you be put off multi-engine flying? It's safe, fun, and productive.

A multi-engine airplane is not inherently difficult. Certain aspects of it's behavior, namely flying with one engine inoperative at low speeds, merit attention, but are easily addressed. The multi-engine airplane is not a flying deathtrap.

If you intend to fly a conventional gear airplane, then learning about handling a tailwheel is in your best interest. It takes specific instruction.

If you intend to fly instruments, then learning about instrument flight is necessary. Specific instruction is required.

If you intend to fly a multi-engine airplane, then dedicated, specific instruction is given. No different than if you intend do do anything else in aviation.

In light multi-engine airplanes, in many cases the loss of one engine will not permit the airplane to retain altitude for long, or at all. Only a few light piston twins have much of a single engine service ceiling. Think of it this way, however; you have a lot more options in the twin than you do in a single, following the loss of one engine. You've also got additional generators, additional hydraulic pumps, additional vacuum pumps, additional fuel pumps and fuel options, etc. With the twin you've got greater all-engine speed, climb performance, and in many cases, comfort.

Then again, you've also got much greater expense.

Multi-engine airplanes shouldn't frighten, but only beg for understanding. Flying one is just another trick in your bag of tricks, nothing more. The single most important thing you need to understand about losing an engine in a light twin comes into play when being slow and carrying power on the good engine, and it's drilled into you time and time again during training until it's a very simple concept to remember and understand; sometimes when directional control becomes an issue, the only remaining choice is to retard power on the good engine. Once that concept is internalized and you understand from experience why you shouldn't get too slow, you realize that losing an engine isn't really an emergency (a concept that your instructor in single engine airplanes should have also instilled). It's just another phase of flight for which you can easily be trained.

[avicon]

Would one of you be kind enough to post complete simulated Vmca demonstration procedure, from initiating Vmca, to recognition of impending vmca, to initial action and recovery.

Thanks in advance.

[FlyingForFun]

Avicon,

The following is provided for information only - please get proper instruction, in an aircraft, from a multi-engine instructor, as part of an approved course!

Other instructors may do this slightly differently, but here's how I do it:

- Perform relevant airmanship actions - safe altituden, appropriate area, good lookout.
- I have control of the aircraft; however, you have control of the rudder.
- Please use the rudder to prevent yaw (using a distant visual feature as a reference, as taught on previous exercises).
- Whilst maintaining pitch, and keeping wings level with ailerons, I gradually close one throttle, expecting you to apply rudder (and trim) to prevent yaw. I then increase power on the other engine until it's at maximum power, again expecting you to apply rudder to prevent yaw.
- I point out to you our current airspeed.
- I pitch the aircraft up, a little at a time, in order to gradually reduce airspeed. After each change in pitch, I wait for you to increase rudder as necessary, and re-trim the rudder, then we look at the new, lower airspeed.
- I repeat this as many times as necessary until you run out of rudder, at which point we note the speed - this is Vmc.

Everything up to this point is a repeat of a previous exercise we've already done, to demonstrate the connection between airspeed and rudder.

- I then pitch up once more, just a tiny bit this time to decrease speed by only a couple of knots. I encourage you to apply more rudder to prevent the yaw, but of course you are unable. Over the next few seconds, the yaw develops into a spiral dive.
- I take control of the rudder ("I have control"), then demonstrate the recovery: close both throttles, lower the nose, then recover to the desired attitude.

Depending on circumstances (student ability, weather, aircraft type, etc), I might repeat this a few times with different scenarios: wings level vs 5 degrees of bank is my favourite, but also critical vs non-critical engine, zero thrust vs windmilling, noting what difference the change makes to Vmc.

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

[Pilot DAR]

Excellent and useful post FFF.

From my place as a non instructor, but tester of such things, I will offer a few additional thoughts to FFF's, though not to contradict....

The Vmca number in the flight manual, which you are aiming for, you may actually find you can better, for two reasons:

If flying a normally aspirated twin at altitude, you started loosing power as you climbed, so you don't have as much asymmetrical power to overcome at altitude. So, you can fly more slowly with the rudder effectiveness you have up there.

The Vmca number is also predicated on a speed at which a sudden loss of power can be managed. You can manage a slower speed, if you creep down to it well prepared.

The weight and C of G of the aircraft may also affect Vmca, though not always as you would expect, so read the flight manual...

[Big Pistons Forever]

I must step in here as I have a big problem of FFF's description.

The point of a "VMC" training (and I think the earlier convoluted debate on VMC vs VMCA was pedantry in the lieu of practicality, but that is another debate) is to teach the student to recognize when the aircraft is approaching VMC and to learn how to effectively recover from this dangerous low speed regime.

It is entirely unnecessary and IMO quite dangerous, to actually slow to a speed where full rudder can no longer control the aircrafts direction. For many common light twin trainers this will result in a speed very close to stalling speed.

A much better way to demonstrate VMC is to, after the aircraft is stabilized with one engine zero thrusted, go to full power on the operating engine and then reduce airspeed while maintaining direction. When I feel the student had put in about 1/2 of total rudder travel I tell the student to apply no more rudder but continue decreasing airspeed. As the aircraft starts to yaw and roll into the dead engine I have the student reduce power on the operating engine and lower the nose to accelerate in order to regain control, which teaches both the recognition of VMC loss of control and to have the student practice the recovery procedure.

Incidentally the closes I have ever come to be killed by a student was on a ME training flight in a PA34 Seneca. The exercise was a engine failure on a go around. We climbed to 4000 ft AGL and set up with gear down flaps full and landing red speed. I then told the student to go around and as he shoved the power up I pulled one throttle back. For some inexplicable reason the student then applied full back stick. Before I could react the aircraft stalled and snapped rolled. I tool over control with the aircraft inverted and 40 degrees nose down:eek:. If I had not been an aerobatic instructor I probably would not have survived. I take single engine work at lower airspeeds very seriously....

[avicon]

Thank you so much FFF.

Just what I wanted. I had done this exercise with my instructor about 9 months ago, and I had forgotten about it all completely. I thought it would be good idea to know what to expect when I do this again later this month during my ME endorsement test.

[FlyingForFun]

Not sure I agree with you, BPF. There are several training benefits of going right down to actual Vmc which I can think of. Safety is, of course, paramount, and your story of the snap roll is sobering, but - my personal opinion, I have no problem if you don't agree - there is no safety issue demonstrating Vmc when I have control of the elevators, ailerons and throttles.Other instructors may do this slightly differently, but here's how I do it:
QED!

(I started typing up the benefits of my method, but then stopped because I feel this conversation really belongs in the Instructors forum rather than Private Flying - it relates solely to instructing technique. If you're interested enough to continue discussing, let's start a new thread in there.)

As for your snap roll, I'll bet you were glad you were at 4000' and not 400'! Makes me wonder how I'd handle that... I haven't done any aeros other than spins for nearly 10 years.

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

[27/09]

There are several training benefits of going right down to actual Vmc which I can think of.

Hmmm, I can't think of any. In fact I can think of some very good reasons why you wouldn't go down to actual Vmc particularly on some twins.

I have to agree with Big Pistons Forever. This is the technique I have used sucessfully for many years.

It's a bit like stalling, where we are not teaching students how to stall the aircraft but teach them how to apply the correct recovery technique, loss of control at Vmca is the same.

[bookworm]

Not sure I agree with you, BPF. There are several training benefits of going right down to actual Vmc which I can think of. Safety is, of course, paramount, and your story of the snap roll is sobering, but - my personal opinion, I have no problem if you don't agree - there is no safety issue demonstrating Vmc when I have control of the elevators, ailerons and throttles.

Depends on the aircraft, doesn't it? Vmca and Vs (in the practical rather than certification sense) are determined by very different features of the aerofoil and controls. On some aircraft, it's easy to reach Vs before Vmca.

In part because it is quite low-powered, the Twin Comanche on a single-engine (and at any altitude at which you would contemplate doing the exercise) retains sufficient rudder authority to maintain directional control right down to the stall. I think there were some nasty accidents in the 60s and 70s involving Vmca "demonstrations" in training situations that resulted stall-spin upsets, and it was as a result that the POH Vmca of the Twin Comanche was raised to the modern 78 KCAS figure, to give the instructors and examiners an excuse to terminate the demonstration after slowing to that speed.

[Pilot DAR]

It is entirely unnecessary and IMO quite dangerous, to actually slow to a speed where full rudder can no longer control the aircrafts direction. For many common light twin trainers this will result in a speed very close to stalling speed.


Though I do not claim to be an expert in this, and am not an instructor, on the whole I don't agree with the generalization that the foregoing would be dangerous. It could be dangerous, but then many things in a plane can be.


In flying at Vmc, not only could you be very close to stalling speed, you could be right there. It is possible, and indeed considered favourable, that a twin reach stalling speed before directional control cannot be maintained with one engine inop.

I'm sure you are aware that the design requirements for these aircraft include: (my bold)

§ 3.123 One-engine-inoperative stalls. Multiengine airplanes shall not display any undue spinning tendency and shall be safely recoverable without applying power to the inoperative engine when stalled with:

(a) The critical engine inoperative,

(b) Flaps and landing gear retracted,

(c) The remaining engines operating at up to 75 percent of maximum continuous power, except that the power need not be greater than that at which the use of maximum control travel just holds the wings laterally level in approaching the stall. The operating engines may be throttled back during the recovery from the stall.

During recent flight testing I was doing in each of two Navajos, I was nervous about entering that phase of flight with the aircraft (both PA-31's, one with wing lockers, the other without). I am not well experienced in Navajos, and suffered from years of hearing hanger talk about how poorly they flew on one engine.

To the contrary, at both forward C of G gross weight, and light aft, I found these two Navajos, both with different external mods, to be very docile in this phase of flight. With the left engine both at idle, and stopped and feathered, and the right at 75% power, stalls were quite controllable.

On some occasions I reached Vmca first, and the stall was performed with either a slight heading change underway, or slightly reduced power on the right. Other times, I reached the stall first.

I have done similar flying in Cessna 300 twins, a King Air 200, and DHC-6, and found them to be similarly agreeable. I have not tried it in the light Piper twins, though the certification requirements would leave me expecting they would be equally compliant.

I agree that mishandling the aircraft can result in unexpected areobatics, and am empathetic to Big Piston's scare. I have found (first from some unsatisfactory experience in my poor briefing) that a very thorough ground briefing as to who will do what, and what that will be, can be a great benifit to a no suprizes flight. I have occasion to be doing this type of flying in aircraft types I have never before flown, and sometimes in the company of other company or safety pilots. I have found that a complete review of the flight test plan [= lesson] (which takes 45 minutes to an hour), and the normal pre takeoff pilot briefing, tailored to the flight, are an excellent way to keep things safe.

In discussing what is to be flown, and what should be, but yet could be expected, everything is out in the open before you leave the ground. For any "newer" pilot reading this, who is in the midst of receiving instruction, do not try to truncate your instructor's ground briefing prior to a lesson. If your instructor requires a half hour of ground briefing, prior to an hour flight, eagerly pay the instructor for that time - particularly if you have questions, or something is new to you. You'll feel very much happier having spent the extra before hand, than having Big Pistons yell "I've got it" as you roll inverted in a Seneca after doing the wrong thing!

[AdamFrisch]

It is important to remember in all single engine asymmetric situations that the one thing that will always get you out of trouble and stabilise things, is to reduce throttle on the good engine.

Have a real engine out scenario and have to make a steep turn into the "dangerous" dead engine to make a field? Reduce throttle. Can't control heading? Reduce throttle. There's nothing that says you're not allowed to do that.

Sometimes in ME training stuff tends to get fixated on "full power on working engine" and it can lead to bad practice at times. I did numerous unstable and semi-scary approaches during my training because I got fixated on this. It's easily done.

[avicon]

I dont suppose there would be critical engine on aircraft with centreline thrust arrangement, would there. Apart from P factor effect diminishing from the loss of one engine(assuming both rotating clockwise), and the degraded climb performance. Correct me if I'm wrong.

Can ME with centreline thrust propellers be considered to behave like a single engine in the event of one engine failure and Vmca not being applicable to them?

[Big Pistons Forever]

Though I do not claim to be an expert in this, and am not an instructor, on the whole I don't agree with the generalization that the foregoing would be dangerous. It could be dangerous, but then many things in a plane can be.


Pilot DAR

First off I would like say that I think your posts are always very informative and I value your contributions to this forum. However I think you have entirely
missed the point I was trying to make by making a common mistake, that is extrapolating your very considerable experience to what should be expected of a low hour student.

It is entirely appropriate that an engineering test pilot explore the full VMC regime because the point of the exercise is to assess compliance with the certification standards. However when teaching the Multi Engine rating demonstrating the actual VMC in certification required configuration is irrelevant. The point of the exercise is teach the student to recognize the onset of a speed below which the aircraft can be directionally controlled and then how to safely recover. This can be just as easily and IMO much more safely, be demonstrated by limiting rudder travel to half travel during the demonstration. I would also like to point out that the flight in which I experienced the upset in the Seneca was preceded, like all my ME instructional flights, with a comprehensive brief which emphasized the importance of lowering the nose to maintain a safe airspeed during an engine failure in an overshoot. Despite that the student in the heat of the moment got everything backwards.....but then that is the challenge of teaching low houred PPL's in complex airplanes, a challenge that does not exist for test pilots flying a very carefully thought out test card.

FFF

I respect what you say but I guess we have a philosophical difference over the conduct of flight training. Your having control of the rudder, elevator and power during a full on VMC makes the manoever safe, but for the manoever to IMO be of full value the student on their own must be able to demonstrate they can control the aircraft. They can obviously only do this if they have their hands on the rudder, elevator, and throttle.....

I guess I have contributed to a conversation that most properly belongs in the instructor forum so my apologies for the thread drift

[AdamFrisch]

Can ME with centreline thrust propellers be considered to behave like a single engine in the event of one engine failure and Vmca not being applicable to them?

Kind of. FAA has a centerline thrust rating only, should you want to do that. There used to be a few Cessna Skymaster pilots with that. The problem is finding an instructor and examiner that is current on that rating - it's easier normally to just do the regular ME rating for that reason.

[Pilot DAR]

what should be expected of a low hour student.



Yes Big Pistons, I quite agree with you. I sometimes see (from the distance) quite a difference in flight instruction techniques, relative to what I know the aircraft should be expected to do. As I am not an instructor, and do not claim to have that skill, I will certainly defer to those pilots who are qualified to instruct. I'm not always at harmony with instructors, but I find I can always learn!

That said, we would all agree that low speed, and particularly asymmetric maneuvers, are the mosy risky. I find that there is a grey zone where we as pilots of more experience are morally bound to not encourage low hour pilots to go "exploring" these risks, but on the other hand, we bear some responsibilty for assuring that these low hour pilots are aware that the aircraft has been designed to behave well in these situations - to a point.

Right or wrong, (and I could be either) I think that new pilots can benefit from experiencing flight a bit beyond "the point", in a artificially safe environment. Hopefully it will be memorable for them in a way which will aid them in getting the most out of the plane when they need to, without creating unsafe situations, or being tempted to "fool around" later.

(And I realize I further thread drift here, pardon me!)

I consider Vmca training to have similarity to spin training in this respect. As I am certain that a low hour pilot should experience a one turn spin during training, I also feel that pilot (during ME training) should experience flight with only one engine developing power, where directional control can no longer be maintianed - just to see what it's like.

Without wanting to offend any instructor, I would state that if training of this type is not being done, because it is thought to be "too dangerous", that sends the wrong message to newer pilots. These maneuvers can be very dangerous, if flown in the wrong circumstances. But if planned, and executed carefully, should have a margin of safety which is acceptable. If that margin of safety is not acceptable because the instructor themself cannot safely recover the possible departure from controlled flight which could result, that's a whole different problem, which, in my opinion, should not be a reason to not demonstrate. I certainly agree that a snap roll in a Seneca is a really bad occurance, but I know that the aircraft should be able to withstand it safely, if the recovery is reasonable. (apparently it can, thanks for the good flying Big Pistons!). I worry that there are instructors avoiding flying anywhere near the stall, because they could not recover such an unusual attitude. I opine that they should be able to, if they are to be instructing on type.

(I drift further, pardon me...)

During a design complince flight test in a club 172, accompanied by an instructor with rank in the club, to "check me out", he asked me to demonstrate a roll. I declined. He pressed a bit, asking, "this plane would roll wouldn't it?". Yes, but I'm not going to do it. I honestly thought it was a trap, to get me to do something stupid. From that expression of loss on his face, I realized that he really did want to experience a roll. Sad for him that he never had. It was not the time/place/airplane on that flight - his loss.

In some of the things I post here, I seek to add my one small voice to those who would say that our industry should not be diluting flight training, particularly because the training of the instructors themselves is being diluted over time. During my low hours training, I was taught spins, 'till I could do them well, I was taught flight with one engine actually feathered in the 310, until I could no longer maintain directional control, and I was taught to loop and roll. I practice these skills as often as the aircraft type permits. I hope the students of this era realize their responsibility in obtaining this type of training from compotent instructors, and gently, yet firmly, assert their right to those learning experiences.

Though the organisation and regulator can set the training curriculum and learnign goals, the student and new pilot play a role in asking for "more", and indicating that that training not being available is not good enough. That said, you lower time pilots..... You bear the responsibility for obtaining that training, taking it seriously, and having the good discipline to not fool around later!

[Big Pistons Forever]

Pilot DAR

First off I think it is important to point out that while my principal flying job is flying an airtanker in aerial forest fire suppression operations I also hold a current Transport Canada Class 1 aeroplane flight Instructor rating and a Class 1 aerobatic instructor rating, so I can situate the theory into the practice when it comes to discussing instruction practices

I am also discouraged by the "dumbing down" of flight instructor ratings. This is IMO particularly egregious with multi engine training which is unfortunately taught by instructors which have little or no actual twin flying experience.

I think all flying instruction should be conducted with a consideration of risk and rewards vs the training objectives. An example of this would e your spin example. Obviously you can not demonstrate a spin without actually stalling the aircraft with enough yaw to allow the aircraft to depart and enter auto rotation. In the case of a VMC demo however the effect of VMC and the procedure to recover from a VMC induced loss of directional control can IMO be just as convincing be demonstrated by limiting rudder travel such that
the MC induced ya occurs at a higher safer speed. Therefore my personal risk reward calculus is that there is no benefit to talking the speed down to actual
VMC.

In any case the problem with VMC is not recovering from a preplanned and briefed VMC demo at altitude, a situation that is unlikely to actually occur in the real world, it is to deal with the low altitude and low speed regime in the case of an EFATO. There is a horrible record of low altitude fatal loss of control accidents after engine failures in light twins.

The current multi engine training syllabus is IMO not doing a very good job of preparing new twin pilots because it is simply too dangerous to do actual low altitude simulated engine failures. The good news is the emerging new generation of flight sims like the Redbird and the alsim now have realistic enough visual systems and flight modelling to allow students to practice the worst case scenarios. I strongly encourage all the light twin student pilots I know to invest in a few hours of training in one of these sims even though the tie can not be counted. It is also vital IMO that anyone flying a light twin take annual recurrent training. If they don't then I think the second engine will only be good for taking them to the scene of the accident......

[Pilot DAR]

Pistons,

I will certainly defer to your qualification as an instructor, and recognize that there are probably valid training techinqes with which I am simply unfamiliar. As long as the recipient of the training is getting either real, or very realistic training, the core aspects have been met.

I have not flown a simulator in 15 years, so they probably have improved a lot since my ATC 810 days. I did fly Flight Safety's Twin Otter sim quite a bit, and found it extremely worthwhile. I was recently told by a very experienced Twin Otter pilot, that he felt it did not represent Vmca in a Twin Otter.

That, however is moot here, as I'm sure that simulator is not readily available to light twin pilots!

I wonder if today's basic simulators have representative control force feedback, so the pilots learns what it feels like. I have no idea though, so I shall leave the sim discussion with those qualified...

Please excuse the continued thread drift!

[englishal]

The thing to do is practice all this with a competent instructor. When I did my ME CPL, the FI failed the engine and then made me do 45° banked turns in both directions - into the failed engine and away from it. It was a useful exercise.

Addition of a vortex kit to some aeroplanes reduce the Vmc to below the stall at any sort of altitude so you'll stall first before you reach Vmc. The dangerous area is where Vmc and Stall coincide so that they occur at exactly the same moment.

[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 withHowever, 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
--------------

[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!)