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Cold Starts May
Cause Unreckoned Engine Damaged
As autumn's nippy weather
turns to winter's chill each year, it's
unfortunately only too predictable that certain
aircraft will have engine-failure accidents due to
the operator's failure to prepare the airplane
properly for cold weather flying.
Common knowledge has it that
the major duty before sub-freezing weather hits is
to change oils, putting in a lighter-weight oil (or
perhaps one of the new multi-viscosity aviation
oils) because of the widespread belief that heavy
oil congeals and clogs the oil cooler or causes the
oil pump to cavitate. This has been a simple and
welcome answer when an accident begs for a
cause-effect relationship to explain a catastrophic
engine failure.
For instance, there was the
crash on February 12, 1984, in which a California
pilot visiting Crested Butte, Colorado lost power
two minutes after takeoff in a Piper Comanche. He
and his three passengers were uninjured in the
emergency landing.
The pilot told investigators
that the airplane had been given about 25 minutes
of preheating in an ambient temperature of 2
degrees Fahrenheit. It was started and run 10 to 15
minutes to "warm it up." The pilot said all
instruments were normal at takeoff.
However, investigators found
the Comanche had been carrying straight 50-weight
oil at the time of the crash - far heavier
viscosity than recommended for cold weather
operations. In addition, line personnel said that
due to the cowling configuration, they had been
unable to insert the preheater duct underneath the
engine so that it would blow hot air around the
crankcase and cylinders, and thus had to lay it
across the top of the engine.
In a somewhat similar vein
was the crash of a Piper Aztec on January 10, 1982
at Palwaukee Airport, Wheeling, Illinois. The
1,640-hour commercial pilot and his passenger
escaped injury when the plane lost both engines
within a couple of minutes after takeoff in IFR
conditions and the pilot had to return to the field
in conditions of an indefinite ceiling and blowing
snow.
The pilot told investigators
he estimated the engines were preheated for 35-45
minutes before startup, and there was a 10-15
minute delay before engine instruments were in the
proper range upon takeoff, he said. By the time the
plane crashed a few minutes later, both engines had
broken connecting rods and gaping holes in the
crankcase.
Investigators soon showed the
plane had been given an oil change the previous
October, when 40-weight oil had been installed. Oil
of 20-weight is recommended for Aztec's engines
when operating below 10 degrees F. The temperature
at the time of the crash was -15 degrees.
And then there was the case
of the 178-hour private pilot and his two
passengers who escaped without injury after
crashing Beech S-35 Bonanza while returning to the
airport with a failed engine after takeoff from
Jackson Hole, Wyoming on January 6, 1982.
The pilot told investigators
he estimated the engines were preheated for 30
minutes before startup and that all instruments
were in the green as the flight launched. Witnesses
said the planes takeoff came only about three
minutes after engine start, however investigators
found 55-weight oil had been installed in the
engine. Temperature at the time of takeoff was -19
degrees Fahrenheit.
While a common thread is
undeniably the grade of oil in use, there is
another element that may link these accidents - the
duration and quality of the preheating service the
planes did (or did not) receive.
There is a possibility that
some engine failure in cold weather are laid to
chance when investigators discover that proper oil
was indeed installed. And there's a possibility
that cold-start damage done to an engine in the
dead of winter may not show up until spring or
summer, when the cause and effect connection may
not be discernable.
One person who has studied
the issue of preheating about as thoroughly as it
can be studied was the late Peter G. Tanis, maker
of an almost unique type of preheater supported for
most aircraft engine types. Along the way, Tanis
happened upon some interesting and even
myth-defying discoveries about engine and cold
weather. We invite readers to consider the points
he raises and judge for themselve.
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