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maximum operating speeds. Good attitude instrument
flying skills and good power control are essential.
The pilot should be aware of the symptoms that will be
experienced in the particular airplane as the VMO or
MMO is being approached. These may include:
• Nosedown tendency and need for back pressure
or trim.
• Mild buffeting as airflow separation begins to
occur after critical Mach speed.
• Actuation of an aural warning device/stick puller
at or just slightly beyond VMO or MMO.
The pilot’s response to an overspeed condition should
be to immediately slow the airplane by reducing the
power to flight idle. It will also help to smoothly and
easily raise the pitch attitude to help dissipate speed (in
fact this is done automatically through the stick puller
device when the high speed warning system is
activated). The use of speed brakes can also aid in
slowing the airplane. If, however, the nosedown stick
forces have progressed to the extent that they are
excessive, some speed brakes will tend to further
aggravate the nosedown tendency. Under most
conditions, this additional pitch down force is easily
controllable, and since speed brakes can normally be
used at any speed, they are a very real asset. A final
option would be to extend the landing gear. This will
create enormous drag and possibly some noseup pitch,
but there is usually little risk of damage to the gear
itself. The pilot transitioning into jet airplanes must be
familiar with the manufacturers’ recommended procedures
for dealing with overspeed conditions contained
in the FAA-approved Airplane Flight Manual for the
particular make and model airplane.
MACH BUFFET BOUNDARIES
Thus far, only the Mach buffet that results from
excessive speed has been addressed. The transitioning
pilot, however, should be aware that Mach buffet is a
function of the speed of the airflow over the wing—
not necessarily the airspeed of the airplane. Anytime
that too great a lift demand is made on the wing,
whether from too fast an airspeed or from too high an
angle of attack near the MMO, the “high speed buffet”
will occur. However, there are also occasions when the
buffet can be experienced at much slower speeds
known as “low speed Mach buffet.”
The most likely situations that could cause the low
speed buffet would be when an airplane is flown at too
slow a speed for its weight and altitude causing a high
angle of attack. This very high angle of attack would
have the same effect of increasing airflow over the
upper surface of the wing to the point that all of the
same effects of the shock waves and buffet would
occur as in the high speed buffet situation.
The angle of attack of the wing has the greatest effect
on inducing the Mach buffet at either the high or low
speed boundaries for the airplane. The conditions that
increase the angle of attack, hence the speed of the
airflow over the wing and chances of Mach buffet are:
• High altitudes—The higher the airplane flies,
the thinner the air and the greater the angle of
attack required to produce the lift needed to
maintain level flight.
• Heavy weights—The heavier the airplane, the
greater the lift required of the wing, and all other
things being equal, the greater the angle of
attack.
• “G” loading—An increase in the “G” loading of
the wing results in the same situation as
increasing the weight of the airplane. It makes
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no difference whether the increase in “G” forces
is caused by a turn, rough control usage, or turbulence.
The effect of increasing the wing’s
angle of attack is the same.
An airplane’s indicated airspeed decreases in relation
to true airspeed as altitude increases. As the indicated
airspeed decreases with altitude, it progressively
merges with the low speed buffet boundary where prestall
buffet occurs for the airplane at a load factor of
1.0 G. The point where the high speed Mach indicated
airspeed and low speed buffet boundary indicated airspeed
merge is the airplane’s absolute or aerodynamic
ceiling. Once an airplane has reached its aerodynamic
ceiling, which is higher than the altitude stipulated in
the FAA-approved Airplane Flight Manual, the airplane
can neither be made to go faster without activating
the design stick puller at Mach limit nor can it be
made to go slower without activating the stick shaker
or stick pusher. This critical area of the airplane’s
　
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