TM 1-1520-238-107A-4Change 2Section II.MAXIMUM TORQUE AVAILABLE7A.9. DESCRIPTION.The maximum torque available charts shows the maxi-mum specification torque available per engine for 30 min-ute operation (fig 7A-2 sheet 1) and 10 minute operation(fig 7A-2 sheet 2) at various conditions of pressure altitudeand free air temperature. Both single and dual engine op-eration limits are shown.The maximum torque available for 2.5 minute operation(fig 7A-2 sheet 3) shows the maximum specificationtorque available when one engine is inoperative; onlysingle engine operation limits are shown.The torque factor charts (figs 7A-3 and 7A-4) provide anaccurate indication of available power for the enginesinstalled in each individual aircraft.7A.10. USE OF CHARTS.The primary use of the maximum torque available charts(fig 7A-2 sheets 1, 2, and 3) is illustrated by the example.To determine the maximum specification torque available,it is necessary to know pressure altitude and free air tem-perature. Enter the left side of either the 30 minute or the10 minute chart (fig 7A-2 sheets 1 or 2) at the known tem-perature and move right to the known pressure altitude,and then move down and read the maximum specificationtorque available. This is torque per engine. For dual en-gine operation, if the torque per engine exceeds the twoengine limit, the maximum torque available must be re-duced to the two engine limit.For one engine inoperative, enter the left side of the 2.5minute limit chart (fig 7A-2 sheet 3) at the known tempera-ture and move right to the known pressure altitude, andthen move down and read the maximum specificationtorque available for one engine. If the torque exceeds theone engine limit, maximum torque available must be re-duced to the one engine limit.7A.11. CONDITIONS.The maximum torque available charts (fig 7A-2 sheets 1,2, and 3) are based on 100% rotor rpm, zero airspeed,JP-4 fuel and ENG INLET anti-ice switch OFF. With ENGINLETanti-ice switch ON, available torque is reduced byas much as 19.3% for 30 minute operation and 18.6% for10 minute operation. For example, if value from the chartis 90%, with anti-ice ON, torque available would be 90 –19.3 = 70.7%, 30 minute limit.7A.12. TORQUE FACTOR METHOD.The torque factor method provides an accurate indicationof available power by incorporating ambient temperatureeffects 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 specificationpower 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 fromthe maximum power check and recorded to be used incalculating maximum torque available.7A.12.1 Torque Factor Terms.The following termsare used when determining the maximum torque availablefor an individual aircraft:a. Torque Ratio (TR).The ratio of torque availableto specification torque at the desired ambient tempera-ture.b. Engine Torque Factor (ETF).The ratio of an in-dividual engine torque available to specification torque atreference temperature of 35 C. The ETF is allowed torange from 0.85 to 1.0.c. Aircraft Torque Factor (ATF).The ratio of an in-dividual aircrafts power available to specification power ata reference temperature of 35 C. The ATF is the averageof the ETFs of both engines and its value is allowed torange from 0.9 to 1.0.7A.12.2 Torque Factor Procedure.The use of theATF or ETF to obtain the TR from figure 7A-3 for ambienttemperatures between –15 C and 35 C is shown by theexample. The ATF and ETF values for an individual air-craft are found on the engine HIT log. The TR alwaysequals 1.0 for ambient temperatures of –15 C and below,and the TR equals the ATF or ETF for temperatures of 35C and above.When the TR equals 1.0 the torque available may be readdirectly from the specification torque available scales.When the TR is less than 1.0, the actual torque availableis 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 7A-4) isprovided to convert specification data to actual torqueavailable. The single and dual engine transmission limitsare shown and should not be exceeded.