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and it becomes apparent that there are three ways in
which the jet pilot is worse off than the propeller pilot.
For these reasons, there is a marked difference between
the approach qualities of a piston engine airplane and a
jet. In a piston engine airplane, there is some room for
error. Speed is not too critical and a burst of power will
salvage an increasing sink rate. In a jet, however, there
is little room for error.
If an increasing sink rate develops in a jet, the pilot
must remember two points in the proper sequence.
1. Increased lift can be gained only by accelerating
airflow over the wings, and this can be
accomplished only by accelerating the entire
airplane.
2. The airplane can be accelerated, assuming
altitude loss cannot be afforded, only by a rapid
increase in thrust, and here, the slow acceleration
of the jet engine (possibly up to 8 seconds)
becomes a factor.
Salvaging an increasing sink rate on an approach in a
jet can be a very difficult maneuver. The lack of ability
to produce instant lift in the jet, along with the slow
acceleration of the engine, necessitates a “stabilized
approach” to a landing where full landing
configuration, constant airspeed, controlled rate of
descent, and relatively high power settings are
maintained until over the threshold of the runway. This
allows for almost immediate response from the engine
in making minor changes in the approach speed or rate
of descent and makes it possible to initiate an
immediate go-around or missed approach if necessary.
ABSENCE OF PROPELLER DRAG
When the throttles are closed on a piston powered
airplane, the propellers create a vast amount of drag,
and airspeed is immediately decreased or altitude lost.
The effect of reducing power to idle on the jet engine,
however, produces no such drag effect. In fact, at an
idle power setting, the jet engine still produces
forward thrust. The main advantage is that the jet pilot
is no longer faced with a potential drag penalty of a
runaway propeller, or a reversed propeller. A
disadvantage, however, is the “free wheeling” effect
forward thrust at idle has on the jet. While this
occasionally can be used to advantage (such as in a
long descent), it is a handicap when it is necessary to
lose speed quickly, such as when entering a terminal
area or when in a landing flare. The lack of propeller
drag, along with the aerodynamically clean airframe
of the jet, are new to most pilots, and slowing the
airplane down is one of the initial problems
encountered by pilots transitioning into jets.
SPEED MARGINS
The typical piston powered airplane had to deal with
two maximum operating speeds.
• VNO—Maximum structural cruising speed,
represented on the airspeed indicator by the
upper limit of the green arc. It is, however,
permissible to exceed VNO and operate in the
caution range (yellow arc) in certain flight
conditions.
• VNE—Never-exceed speed, represented by a red
line on the airspeed indicator.
These speed margins in the piston airplanes were
never of much concern during normal operations
because the high drag factors and relatively low cruise
power settings kept speeds well below these maximum
limits.
Maximum speeds in jet airplanes are expressed
differently, and always define the maximum operating
speed of the airplane which is comparable to the VNE
of the piston airplane. These maximum speeds in a jet
airplane are referred to as:
• VMO—Maximum operating speed expressed in
terms of knots.
• MMO—Maximum operating speed expressed in
terms of a decimal of Mach speed (speed of
sound).
To observe both limits VMO and MMO, the pilot of a jet
airplane needs both an airspeed indicator and a
Machmeter, each with appropriate red lines. In some
general aviation jet airplanes, these are combined into
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a single instrument that contains a pair of concentric
indicators, one for the indicated airspeed and the other
for indicated Mach number. Each is provided with an
appropriate red line. [Figure 15-8]
A more sophisticated indicator is used on most
jetliners. It looks much like a conventional airspeed
indicator but has a “barber pole” that automatically
moves so as to display the applicable speed limit at all
times.
Because of the higher available thrust and very low
drag design, the jet airplane can very easily exceed its
speed margin even in cruising flight, and in fact in
　
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