CFI-to-CFI Newsletter - Volume 8 Issue 2 - 17

CFI TIPS
THE NEARLY 1,400-HOUR CFI APPARENTLY DIDN'T REMEMBER THAT WHEN ICE IS PRESENT AND CARB HEAT IS APPLIED, THE
ENGINE MAY RUN ROUGH AS THE ICE MELTS AND IS CARRIED INTO THE ENGINE. THE ENGINE WILL RUN SMOOTHER AFTER THE
ICE HAS MELTED.
LEARNING ABOUT WEATHER, AND ITS IMPACT ON
THE DECISION OF WHETHER or not to begin or

complete a flight as planned, can be a challenging
concept for students. From thunderstorms to
icing and everything in between, there is a lot
to learn. CFIs can help by setting a positive
example when it comes to weather-related
decision making. Knowing the circumstances
of weather-related accidents can also help CFIs
to understand what can go wrong, and use that
knowledge to focus lessons on specific weather
phenomena. The following examples show what
can happen on instructional flights when CFIs
aren't weather wise.
On January 11, 2012, a CFI and student pilot
survived a forced landing in a Cessna 150
near the Fitchburg Municipal Airport in
Massachusetts. On this cold New England
morning, the air temperature was -1 C. During
preflight, the student plugged in the preheater
and cleaned the frost off the windows (the
wings and horizontal stabilizer were free of

frost because they had been covered). After
preflight, the engine start took four to five
attempts, with increasing use of primer, before
it finally started.
The flight was uneventful until on climbout
after a touch and go when the engine began
running rough. The CFI applied carb heat,
which made the engine run rougher, so the
CFI turned off the carb heat. At that point the
engine was still running rough but not as much
as when the carb heat was applied. Not knowing
if the aircraft would be able to maintain level
flight, the CFI determined that at their airspeed
and altitude the best course of action was to
continue straight ahead rather than attempt to
turn back to the airport. After about 20 seconds
the aircraft descended into trees before hitting
the ground.
At the time of the accident, the temperature
was 0 C, the dewpoint was -4 C, and the relative
humidity was 72 percent. FAA Advisory

Circular 91-51A states that carb ice can occur
at temperatures between -7 C and 21 C when
there is high humidity or visible moisture.
The nearly 1,400-hour CFI apparently didn't
remember that when ice is present and carb heat
is applied, the engine may run rough as the ice
melts and is carried into the engine. The engine
will run smoother after the ice has melted. The
National Transportation Safety Board (NTSB)
determined the probable cause(s) to be "a
partial loss of engine power due to the formation
of carburetor ice and the flight instructor's
improper application of carburetor heat."
In March of that same year, a Cessna 150 with a
CFI and student pilot on board encountered VFR
into IMC conditions after departing Pearson
Field in Vancouver, Washington. It's unusual for
an instructional flight to succumb to VFR into
IMC, but like most accidents of this type, it was
fatal. In fact, VFR into IMC accidents are fatal
almost 90 percent of the time.

Table of Contents for the Digital Edition of CFI-to-CFI Newsletter - Volume 8 Issue 2