Page 19 - March 25

occurs when the Ng stops turning, when the ITT drops off
the cliff, when the oil pressure reads below minimums.
A traditional single engine failure usually has a whole
host of caution/advisory lights illuminated and the
gauges read so low that the offending engine is easy to
identify. It is certainly a terrible potential, especially if
the failure occurs at a critical time in flight. An engine
failure just after takeoff can be deadly and the training
community is right to train pilots to handle engine
failures. But can an engine lose the ability to produce
torque and not fail? Can a PT6 engine lose the ability
to produce thrust but still have normal oil pressure and
normal (albeit lower) ITT readings? Can a PT6 engine
lose the ability to respond to pilot input? Yes, it can.
It is called a power rollback, and it is a potential that
I believe is one of the least understood emergencies in
the King Air community.
Two of my favorite airplanes to fly are the Piper Mirage
with the JetPROP conversion (hereafter referred to as
JetPROP) and the TBM 7XX/850. Both are equipped
with a PT6 engine and both have a prop lever to feather
the prop. Some other single-engine airplanes (Meridian,
M500, M600, M700) lack a prop lever, meaning the prop
can only be feathered by shutting down the engine.
However, in the JetPROP and TBM, the prop can be
feathered by pulling the prop lever all the way aft, making
it a useful feature in a training environment.
If you fly a JetPROP to a safe altitude (VMC conditions),
you can bring the power lever to idle and feather the prop.
If the pilot then pitches for 110 KIAS (an ideal gliding
speed in this airplane) in a no-wind scenario, the rate
of descent will be about 700 feet per minute, and the
descent angle (observed with the flight path marker)
will be 3.5 degrees down. This demonstrates that the
JetPROP is a phenomenal glider with remarkable gliding
characteristics in the event of an engine failure.
In a training event, I’ll then advance the prop lever back
to full forward and adjust the power lever to achieve 700
fpm and a 3.5 descent angle. Usually, this torque setting
is 160 feet/lbs, equating to zero thrust (equitable drag
as an airplane with a feathered prop). This is important
because it is possible to know zero-thrust with the prop
spinning at 2,200 rpm.
1st Source Bank
MARCH 2025 KING AIR MAGAZINE •
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