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power, particularly high asymmetrical power,
a spin entry is likely. The yawing moment induced
from asymmetrical thrust is little different from that
induced by full rudder in an intentional spin in the
appropriate model of single-engine airplane. In this
case, however, the airplane will depart controlled
flight in the direction of the idle engine, not in the
direction of the applied rudder. Twins are not required
to demonstrate recoveries from spins, and their spin
recovery characteristics are generally very poor.
Where VS is encountered at or before VMC, the departure
from controlled flight may be quite sudden, with
strong yawing and rolling tendencies to the inverted
position, and a spin entry. Therefore, during a VMC
demonstration, if there are any symptoms of an
impending stall such as a stall warning light or horn,
airframe or elevator buffet, or rapid decay in control
effectiveness, the maneuver should be terminated
immediately, the angle of attack reduced as the throttle
is retarded, and the airplane returned to the entry
airspeed. It should be noted that if the pilots are
wearing headsets, the sound of a stall warning horn
will tend to be masked.
The VMC demonstration only shows the earliest onset
of a loss of directional control. It is not a loss of control
of the airplane when performed in accordance with
the foregoing procedures. A stalled condition should
never be allowed to develop. Stalls should never be
performed with asymmetrical thrust and the VMC
demonstration should never be allowed to degrade into
a single-engine stall. A VMC demonstration that is
allowed to degrade into a single-engine stall with high
asymmetrical thrust is very likely to result in a loss of
control of the airplane.
An actual demonstration of VMC may not be possible
under certain conditions of density altitude, or with
airplanes whose VMC is equal to or less than VS. Under
those circumstances, as a training technique, a demonstration
of VMC may be safely conducted by artificially
limiting rudder travel to simulate maximum available
rudder. Limiting rudder travel should be accomplished
at a speed well above VS (approximately 20 knots).
Density Altitude
Indicated Airspeed
Stall
Occurs
First
Yaw
Occurs
First
Recovery
May Be
Difficult
Altitude Where
VMC = Stall Speed
Engine-Out
Power-On
Stall Speed (VS)
VMC
Figure 12-21. Graph depicting relationship of VMC to VS.
Ch 12.qxd 5/7/04 9:55 AM Page 12-30
The rudder limiting technique avoids the hazards of
spinning as a result of stalling with high asymmetrical
power, yet is effective in demonstrating the loss of
directional control.
The VMC demonstration should never be performed
from a high pitch attitude with both engines operating
and then reducing power on one engine. The preceding
discussion should also give ample warning as to why
engine failures are never to be performed at low airspeeds.
An unfortunate number of airplanes and pilots
have been lost from unwarranted simulated engine
failures at low airspeeds that degenerated into loss of
control of the airplane. VSSE is the minimum airspeed
at which any engine failure should be simulated.
MULTIENGINE TRAINING
CONSIDERATIONS
Flight training in a multiengine airplane can be safely
accomplished if both the instructor and the student are
cognizant of the following factors.
• No flight should ever begin without a thorough
preflight briefing of the objectives, maneuvers,
expected student actions, and completion standards.
• Aclear understanding must be reached as to how
simulated emergencies will be introduced, and
what action the student is expected to take.
The introduction, practice, and testing of emergency
procedures has always been a sensitive subject.
Surprising a multiengine student with an emergency
without a thorough briefing beforehand has no place
in flight training. Effective training must be carefully
balanced with safety considerations. Simulated engine
failures, for example, can very quickly become actual
emergencies or lead to loss of the airplane when
approached carelessly. Pulling circuit breakers can
lead to a subsequent gear up landing. Stall-spin accidents
in training for emergencies rival the number of
stall-spin accidents from actual emergencies.
All normal, abnormal, and emergency procedures can
and should be introduced and practiced in the airplane
as it sits on the ground, power off. In this respect, the
airplane is used as a cockpit procedures trainer (CPT),
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