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speed. Now formally defined in Title 14 of the
Code of Federal Regulations (14 CFR) part 23,
Airworthiness Standards, and required to be
established and published in the AFM/POH. It is
the minimum speed to intentionally render the
critical engine inoperative.
• VMC – Minimum control speed with the critical
engine inoperative. Marked with a red radial line
on most airspeed indicators. The minimum speed
at which directional control can be maintained
under a very specific set of circumstances outlined
in 14 CFR part 23, Airworthiness Standards.
Under the small airplane certification regulations
currently in effect, the flight test pilot must be able
to (1) stop the turn that results when the critical
engine is suddenly made inoperative within 20°
of the original heading, using maximum rudder
deflection and a maximum of 5° bank, and (2)
thereafter, maintain straight flight with not
more than a 5° bank. There is no requirement in
this determination that the airplane be capable
of climbing at this airspeed. VMC only
addresses directional control. Further discussion
of VMC as determined during airplane certification
and demonstrated in pilot training
follows in minimum control airspeed (VMC)
demonstration. [Figure 12-1]
Figure 12-1. Airspeed indicator markings for a multiengine
airplane.
Unless otherwise noted, when V speeds are given in
the AFM/POH, they apply to sea level, standard day
conditions at maximum takeoff weight. Performance
speeds vary with aircraft weight, configuration, and
atmospheric conditions. The speeds may be stated in
statute miles per hour (m.p.h.) or knots (kts), and they
may be given as calibrated airspeeds (CAS) or indicated
airspeeds (IAS). As a general rule, the newer
AFM/POHs show V speeds in knots indicated airspeed
(KIAS). Some V speeds are also stated in knots calibrated
airspeed (KCAS) to meet certain regulatory
requirements. Whenever available, pilots should operate
the airplane from published indicated airspeeds.
With regard to climb performance, the multiengine
airplane, particularly in the takeoff or landing configuration,
may be considered to be a single-engine
airplane with its powerplant divided into two units.
There is nothing in 14 CFR part 23 that requires a
multiengine airplane to maintain altitude while in
the takeoff or landing configuration with one engine
inoperative. In fact, many twins are not required to
do this in any configuration, even at sea level.
The current 14 CFR part 23 single-engine climb
performance requirements for reciprocating enginepowered
multiengine airplanes are as follows.
• More than 6,000 pounds maximum weight
and/or VSO more than 61 knots: the singleengine
rate of climb in feet per minute (f.p.m.) at
5,000 feet MSL must be equal to at least .027
VSO
2. For airplanes type certificated February 4,
1991, or thereafter, the climb requirement is
expressed in terms of a climb gradient, 1.5 percent.
The climb gradient is not a direct equivalent
of the .027 VSO
2 formula. Do not confuse the
date of type certification with the airplane’s
model year. The type certification basis of many
multiengine airplanes dates back to CAR 3 (the
Civil Aviation Regulations, forerunner of today’s
Code of Federal Regulations).
• 6,000 pounds or less maximum weight and VSO
61 knots or less: the single-engine rate of climb
at 5,000 feet MSL must simply be determined.
The rate of climb could be a negative number.
There is no requirement for a single-engine
positive rate of climb at 5,000 feet or any other
altitude. For light-twins type certificated
February 4, 1991, or thereafter, the singleengine
climb gradient (positive or negative) is
simply determined.
Rate of climb is the altitude gain per unit of time, while
climb gradient is the actual measure of altitude gained
per 100 feet of horizontal travel, expressed as a percentage.
An altitude gain of 1.5 feet per 100 feet of
travel (or 15 feet per 1,000, or 150 feet per 10,000) is a
climb gradient of 1.5 percent.
There is a dramatic performance loss associated with
the loss of an engine, particularly just after takeoff.
Any airplane’s climb performance is a function of
thrust horsepower which is in excess of that required
12-2
Ch 12.qxd 5/7/04 9:54 AM Page 12-2
for level flight. In a hypothetical twin with each engine
producing 200 thrust horsepower, assume that the total
level-flight thrust horsepower required is 175. In this
situation, the airplane would ordinarily have a reserve
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