TM 1-1520-238-107-4Change 2Section II.MAXIMUM TORQUE AVAILABLE7.9 DESCRIPTION.The maximum torque available chart shows the maximumspecification torque available per engine for 30 minute op-eration (fig 7-2 sheet 1) at various conditions of pressurealtitude 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 specificationtorque available when one engine is inoperative; onlysingle 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 enginesinstalled 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. Todetermine the maximum specification torque available, 30minute limit, it is necessary to know pressure altitude andfree air temperature. Enter the left side of the chart (fig 7-2sheet 1) at the known temperature and move right to theknown pressure altitude, and then move down and readmaximum specification torque available, 30 minute limit.This is torque per engine. For dual engine operation, if thetorque per engine exceeds the two-engine limit, the maxi-mum torque available must be reduced to the two enginelimit.For one engine inoperative, enter the left side of the 2.5minute limit chart (fig 7-2 sheet 2) 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.7.11 CONDITIONS.The maximum torque available charts (fig 7-2 sheets 1and 2) are based on 100% rotor rpm, zero airspeed, JP-4fuel and ENG INLET anti-ice switch OFF. With ENG IN-LETanti-ice switch ON, available torque is reduced by asmuch as 16%. For example, if the value from the 30-min-ute limit chart is 90%, with anti-ice ON, torque availablewould be 90 – 16 = 74%.7.12 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.7.12.1 Torque Factor Terms.The following terms areused when determining the maximum torque available foran 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 1.0.7.12.2 Torque Factor Procedure.The use of the ATFor 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 aircraftare found on the engine HIT log. The TR always equals1.0 for ambient temperatures of –15 C and below, andthe TR equals the ATF or ETF for temperatures of 35 Cand above.When the TR equals 1.0 the torque available may be readdirectly from the specification torque available scalesWhen 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 7-4) isprovided to convert specification data to actual torqueavailable. The single and dual engine transmission limitsare shown and should not be exceeded.