User Guide

Flight Instruction
215
The other turbine (called the power turbine) and propeller
can spin up to idle RPM at their own speed; as they do, oil pres-
sure from the gas generator section will unfeather the blades.
The other clue is that where you’d expect a big jet exhaust
at the back of the engine nacelle, there’s either nothing or an
optional baggage locker! Instead, there are two big exhaust pipes
at the front of the engine, right behind the propeller. This is
because in the King Air (and every other airplane except those
with “pusher props” such as the Piaggio Avanti), the PT6-A is a
reverse flow engine. It’s actually mounted backward in the cowl-
ing, with its intake at the rear. Air entering through the scoop just
below the prop flows aft through the cowling and makes a U-turn
to enter the engine. Then it works its way forward through the
compressors, combustion chamber, and turbines before making
another U-turn in the exhaust stacks. It’s a very handy arrange-
ment: the shaft from the gas generator turbine goes aft into the
engine to spin the compressor, while the one from the power tur-
bine goes forward to the gearbox and propeller.
There’s an additional benefit to this arrangement: engine ice
protection. With its fragile compressor blades spinning at close to
40,000 RPM, the engine is vulnerable to damage if it ingests any ice.
On the Super King Air, the inlet lip is heated with exhaust gas. In
normal operation, air flows straight back into the cowling and enters
the engine. In icing conditions, however, doors and vanes are
deployed to form an inertial separator. The air must make a sharp
turn to enter the engine. Ice particles, however, are too heavy to do
so, so they “skid out” of the turn and are dumped overboard through
the open bypass door at the rear of the cowling.
Exhaust
Induction Air Inlet
Exhaust Heated
Engine Air Inlet Lip
Baffle
Screen
Inertial Vane
Bypass Door
Inertial Vane
PT6-A Reverse Flow Engine
Front
Rear
Intake
Exhaust
Ice Protection System
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Flight Instruction
IN THE COCKPIT
OK, walk up through the roomy cabin and settle into the
pilot’s seat. It may take a bit of gymnastics to do so, since many
King Airs are equipped with a double-width center pedestal,
between the seats, to accommodate optional equipment. Take a
look around. At first, it may seem there are an awful lot of switch-
es, dials, and gadgets; but they’re very logically grouped, and
you’ll soon find your way around easily among them.
Let’s start at the very top. A row of knobs in the ceiling con-
trols the brightness of various groups of instrument and panel
lights, but you only have to set them once; just to their left, a sin-
gle switch turns them all on and off together. Just above it is a knob
for the windshield wipers.
Just above the top of the windshield are three meters to mon-
itor the electrical system. The left two are for the starter-generators
on each engine (on most turbines, a single unit serves both func-
tions - run DC back into a generator, and it becomes an electric
motor!). Each reads the output of its unit in amps; to read volts,
push the button at the 7 o’clock position. The other meter, to the
right, monitors the 400-Hz AC supply used by some instruments
and avionics, indicating voltage in its normal mode (should be 115
volts) and frequency when its button is pushed.
Generator Load
Left/Right
AC Voltage
Compass
Panel Lights
King Air Upper Panel
Master Panel Lights
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