MAXIMUM TORQUE AVAILABLE
The maximum torque available chart shows the maximum
specification torque available per engine for 30 minute op-
eration (fig 7-2 sheet 1) at various conditions of pressure
altitude and free air temperature. Both single and dual en-
gine operation limits are as shown.
The maximum torque available chart for 2.5 minute opera-
tion (fig 7-2 sheet 2) shows the maximum specification
torque available when one engine is inoperative; only
single engine operation limits are shown.
The torque factor charts (figs 7-3 and 7-4) provide an ac-
curate indication of available power for the engines
installed in each individual aircraft.
7.10 USE OF CHARTS.
The primary use of the maximum torque available charts
(fig 7-2 sheets 1 and 2) is illustrated by the example. To
determine the maximum specification torque available, 30
minute limit, it is necessary to know pressure altitude and
free air temperature. Enter the left side of the chart (fig 7-2
sheet 1) at the known temperature and move right to the
known pressure altitude, and then move down and read
maximum specification torque available, 30 minute limit.
This is torque per engine. For dual engine operation, if the
torque per engine exceeds the two-engine limit, the maxi-
mum torque available must be reduced to the two engine
For one engine inoperative, enter the left side of the 2.5
minute limit chart (fig 7-2 sheet 2) at the known tempera-
ture and move right to the known pressure altitude, and
then move down and read the maximum specification
torque available for one engine. If the torque exceeds the
one engine limit, maximum torque available must be re-
duced to the one engine limit.
The maximum torque available charts (fig 7-2 sheets 1
and 2) are based on 100% rotor rpm, zero airspeed, JP-4
fuel and ENG INLET anti-ice switch OFF. With ENG IN-
LET anti-ice switch ON, available torque is reduced by as
much as 16%. For example, if the value from the 30-min-
ute limit chart is 90%, with anti-ice ON, torque available
would be 90 16 = 74%.
7.12 TORQUE FACTOR METHOD.
The torque factor method provides an accurate indication
of available power by incorporating ambient temperature
effects on degraded engine performance. The torque fac-
tor method provides the procedure to determine the maxi-
mum dual or single engine torque available for the en-
gines installed in each individual aircraft. The specification
power is defined for a newly delivered low time engine.
The aircraft HIT log form for each engine provide the en-
gine and aircraft torque factors which are obtained from
the maximum power check and recorded to be used in
calculating maximum torque available.
7.12.1 Torque Factor Terms.
The following terms are
used when determining the maximum torque available for
an individual aircraft:
a. Torque Ratio (TR).
The ratio of torque available
to specification torque at the desired ambient tempera-
b. Engine Torque Factor (ETF).
The ratio of an in-
dividual engine torque available to specification torque at
reference temperature of 35 C. The ETF is allowed to
range from 0.85 to 1.0.
c. Aircraft Torque Factor (ATF).
The ratio of an in-
dividual aircrafts power available to specification power at
a reference temperature of 35 C. The ATF is the average
of the ETFs of both engines and its value is allowed to
range from 0.9 to 1.0.
7.12.2 Torque Factor Procedure.
The use of the ATF
or ETF to obtain the TR from figure 7-3 for ambient tem-
peratures between 15 C and 35 C is shown by the ex-
ample. The ATF and ETF values for an individual aircraft
are found on the engine HIT log. The TR always equals
1.0 for ambient temperatures of 15 C and below, and
the TR equals the ATF or ETF for temperatures of 35 C
When the TR equals 1.0 the torque available may be read
directly from the specification torque available scales
When the TR is less than 1.0, the actual torque available
is determined by multiplying the specification torque avail-
able by the TR (example for TR = 0.98: 90% TRQ X 0.98
= 88.2% TRQ). The torque conversion chart (fig 7-4) is
provided to convert specification data to actual torque
available. The single and dual engine transmission limits
are shown and should not be exceeded.