TM 55-2840-231-23
1-72. HEALTH INDICATOR TEST (HIT)
INITIAL SETUP
Applicable Configuration
References
All
AIRFRAME/
1. Health Indicator Test
(HIT)
TM 55-1520-214-10
TM 55-1520-228-10
The HIT is the method by which a pilot, in
day-to-day flying, monitors the aircraft
engine condition. This is accomplished by the
pilot selecting an N1 setting (%) based on the
existing outside air temperature (OAT)
observed on the aircraft OAT gauge. The TOT
indicated at that N1 setting must then relate
to the predicted value (Baseline TOT Value)
found on the HIT Log. TOT variations from
the baseline values are logged by the pilot on
the appropriate HIT Log. This log, is then
used by maintenance personnel as an aid in
monitoring engine health trend data.
Several readings less than the
established baseline value (minus
indications) may be an indication
of inaccuracies in the TOT, N1, or
OAT indicating systems or an
erroneous baseline and should
be investigated and corrected.
(Far example, a HIT indication of
– 15 degrees could mean that the
indicating systems may be
displaying a lower value than the
actual present value. Given this
example, if the engine is
operated at or near an N1 or
TOT limit, it may well be
operating beyond limitations
while indicating to the pilot
operations within published
limits.)
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