Vmc Training

[john_tullamarine]

As the subject of Vmca regularly pops up in this, and other, forums, the following recent advice from a major regulatory body may be useful for ME instructors, and ME pilots generally, to review.

quote

THE Vmc DEMO

Both the private and commercial practical test standards for a multiengine class rating require a Vmc demonstration. Previous PTS Books (FAA-S-8081-12A and FAA-S-8081-14) contained a "NOTE" reference this task which advised that airplanes with normally aspirated engines will lose power as altitude increases, and the loss of power may result in a Vmc lower than stall speed at higher altitudes. Also, some airplanes have such an effective rudder that even at sea level Vmc is lower than stall speed. The note went on to say that in these airplanes a demonstration of loss of directional control may be safely conducted by limiting rudder travel to simulate maximum available rudder. The information in this note was intended to be informative rather than directive.

The information regarding limiting rudder travel to simulate maximum available rudder does not appear in the new practical test standards which become effective August 1, 2002, and as an answer to questions we have received regarding this issue, we would like to emphasize that the omission is intentional. It is FAA policy that "blocking the rudder" during the Vmc demonstration task on a practical test is not an acceptable method of demonstrating or evaluating this maneuver. During training however, single engine procedures should be practiced to prepare for an actual emergency situation, not just a practical test demonstration. In the training situation "blocking the rudder" has been, and will continue to be, an acceptable and productive method of teaching single engine procedures. As recovery ability is gained with practice, the speed at which the maneuver is started may be lowered in small increments until the feel of the aircraft in emergency conditions is well known. Practice should be continued until an instinctive corrective reaction is developed, and the corrective procedure is automatic. In a training situation, restricting rudder travel in effect sets up an artificial situation which is very useful in the interest of safety. By the time a student's training is complete, and he/she is ready for a practical test, the student should be well versed in the effects of density altitude on Vmc, the relationship of Vmc to stall speed, reasons for loss of directional control, indications of loss of directional control, loss of directional control recovery procedure, and the critical importance of never allowing the airplane to enter a stall with one engine inoperative. This is what the
applicant will demonstrate on the practical test, not just the ability to mechanically approach a loss of control situation and recover.

It must be remembered that the practical test standards are designed to be "testing documents" rather than "teaching documents". The practical test standard books contain the standards to which a particular maneuver/procedure must be accomplished. Information on teaching and performing specific maneuvers is contained in the Airplane Flying Handbook (FAA-H-8083-3) and the Pilot's Operating Handbook for the specific make and model airplane. The practical test standards do not require an actual loss of control on a Vmc demonstration. This has not changed. The practical test standards require that an applicant recognize any indications of loss of directional control, or stall warning, or stall buffet, and recovers promptly and correctly when either is encountered.

Artificially limiting rudder travel defeats this purpose. Pilot's Operating Handbooks for popular light twin engine training airplanes such as Piper PA-34, PA-31, PA-44, Cessna 402, BE-76 and BE-58 make no mention of limiting rudder travel during Vmc demonstrations on FAA practical tests. Almost invariably the POH's for these and other aircraft recommend that recovery be initiated at Vmc, stall warning, or stall buffet, as in the Practical Test Standards.

unquote

[Centaurus]

Quite so! Well not for this little black duck.

A Vmca "departure" is a frightening experience. If mis-handling of the Vmca manoeuvre occurs and the aircraft departs controlled flight with full power on one engine, the following graphic description from the Beechcraft Baron B55 POH page 10-26 will ensure that your whole day will be ruined.

If this procedure is not followed and the airplane allowed to become fully stalled while on engine is providing lift-producing thrust, a rapid rolling and yawing motion may develop even against full aileron and rudder, resulting in the airplane becoming inverted during the onset of a spinning motion.

My answer is stuff that for a joke. If the examiner wants to take the Vmca demonstration right up to full rudder then he would be gone a million in a duty of care legal opinion - if he survives the spin.

[Blue Hauler]

Risk management could be addressed something like this:

 Establish the aircraft in the appropriate configuration at 2,000 feet.
 Reduce power on both engines and maintain altitude until stall is imminent and note speed and recover.
 Fail the critical engine for the Vmca demonstration.
 If Vmca is not achieved at ten knots above the stall, leave foot under the active rudder pedal and immediately simulate Vmca.
 If Vmca is achieved at or better than ten knots above the stall then the exercise has been successful.
 In either event recover closing both throttles and lowering the nose.
 Clean-up, climb out and continue with the rest of the training.