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for landing.
For spin avoidance when practicing engine failures,
the flight instructor should pay strict attention to the
maintenance of proper airspeed and bank angle as the
student executes the appropriate procedure. The
instructor should also be particularly alert during stall
and slow flight practice. Forward center-of-gravity
positions result in favorable stall and spin avoidance
characteristics, but do not eliminate the hazard.
When performing a VMC demonstration, the instructor
should also be alert for any sign of an impending stall.
The student may be highly focused on the directional
control aspect of the maneuver to the extent that
impending stall indications go unnoticed. If a VMC
demonstration cannot be accomplished under existing
conditions of density altitude, it may, for training purposes,
be done utilizing the rudder blocking technique
described in the following section.
As very few twins have ever been spin-tested (none
are required to), the recommended spin recovery
techniques are based only on the best information
available. The departure from controlled flight may
be quite abrupt and possibly disorienting. The direction
of an upright spin can be confirmed from the turn
needle or the symbolic airplane of the turn coordinator,
if necessary. Do not rely on the ball position or other
instruments.
If a spin is entered, most manufacturers recommend
immediately retarding both throttles to idle, applying
full rudder opposite the direction of rotation, and
applying full forward elevator/stabilator pressure (with
ailerons neutral). These actions should be taken as near
simultaneously as possible. The controls should then
be held in that position. Recovery, if possible, will take
considerable altitude. The longer the delay from entry
until taking corrective action, the less likely that recovery
will be successful.
ENGINE INOPERATIVE—LOSS OF
DIRECTIONAL CONTROL
DEMONSTRATION
An engine inoperative—loss of directional control
demonstration, often referred to as a “VMC demonstration,”
is a required task on the practical test for a
multiengine class rating. A thorough knowledge of
the factors that affect VMC, as well as its definition,
is essential for multiengine pilots, and as such an
essential part of that required task. VMC is a speed
established by the manufacturer, published in the
AFM/POH, and marked on most airspeed indicators
with a red radial line. The multiengine pilot must
understand that VMC is not a fixed airspeed under all
conditions. VMC is a fixed airspeed only for the very
specific set of circumstances under which it was
determined during aircraft certification. [Figure 12-19]
In reality, VMC varies with a variety of factors as
outlined below. The VMC noted in practice and
demonstration, or in actual single-engine operation,
could be less or even greater than the published
value, depending upon conditions and technique.
In aircraft certification, VMC is the sea level 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 then
maintain straight flight at the same speed with an angle
of bank of not more than 5°.
The foregoing refers to the determination of VMC under
“dynamic” conditions. This technique is only used by
highly experienced flight test pilots during aircraft certification.
It is never to be attempted outside of these
circumstances.
In aircraft certification, there is also a determination of
VMC under “static,” or steady-state conditions. If there
is a difference between the dynamic and static speeds,
the higher of the two is published as VMC. The static
determination is simply the ability to maintain straight
flight at VMC with a bank angle of not more than 5°. This
more closely resembles the VMC demonstration required
in the practical test for a multiengine class rating.
The AFM/POH-published VMC is determined with the
“critical” engine inoperative. The critical engine is the
Ch 12.qxd 5/7/04 9:55 AM Page 12-27
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engine whose failure has the most adverse effect on
directional control. On twins with each engine rotating
in conventional, clockwise rotation as viewed from the
pilot’s seat, the critical engine will be the left engine.
Multiengine airplanes are subject to P-factor just as
single-engine airplanes are. The descending propeller
blade of each engine will produce greater thrust than
　
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