The system
is
apneumatic-
ally operated, two- axis au-
tomatic control installation
superimposedupon the pri-
mary flight control sys-
tems. An elec
tro- vacuum-
powered turn coordinator
supplies pneumatic inputs
to servo units that link to
the aileron and rudder con-
trol systems. Since the
engine- driven vacuum pump
is
the power source, P.C.
is
operative whenever the
propeller
is
windmilling
at more than 1000 RPM.
CUTOFF
VALVE
BUTTON
FIGURE
2-3.
P.C.
SYSTEM CONTROLS
The thumb-operatedcutoff button on the left hand grip of the
pilot's control wheel
is
shown in Figure
2-
3.
Depressing
this button any time during flight will render the Positive
Contrpl system completely inoperative for flight maneuvers
or
mhual flying. Whenthe cutoff valve button
is
released,
.the aircraft will return unassisted to wings-level flight.
P.C. can be manually overriden with little effort if the sys-
tem should malfunction. Manually over-powering the sys-
tem will not damage the aircraft or the P.C. components.
The
roll-tr.im knob on the turn coordinator, as shown in
Ffgure
2-
3,
provides an aileron trim function through the
P.C.
system. Rotating the knob trims the aircraft about
its roll
axis
to compensate for asymetrical fuel and pas-
senger loadings.
The P.C. system
is
installed to help alleviate pilot fatigue.
But
like any other system in the aircraft, P.C. must be
monitored frequently to check for proper functioning.
The Executive
21
(M20F)
is
certified as aNormal Category
aircraft. No acrobatic maneuvers including spins are ap-
proved. However,
if
a
spin
is
inadvertently approached or
entered, depressing the cutoff valve button on the left
hand-
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