JT15D ATA 77

Pratt & Whitney JT15D Series (CAT C)

ATA 77 ENGINE INDICATING

Page 1 of 8 FOR TRAINING PURPOSES ONLY JT15D - ISSUE 1, 2009





0 TABLE OF CONTENTS

1 Inter turbine temperature sensing system (T5) 3 1.1 Purpose 3 1.2 T1 harness 3 1.3 T6 harness 3 1.4 Variable resistor 3 1.5 Operation 4 2 T5 system calibration 5 2.1 Purpose 5 2.2 Operation 5 2.3 Maintenance 6




1 INTERTURBINE TEMPERATURE SENSING SYSTEM (T5)

1.1 Purpose

The T5 sensing system indicates the engine temperature at station no. 5.

1.2 T1 Harness

The T1 harness consists of a braided harness incorporating two temperature probes (T2.6 and T2), each containing three thermocouples. The T2 probe is located on the inlet case before the fan (JT15D-1 and 4 series). The

T2 probes are located in the airframe inlet cowling before the fan (JT15D- series).

The T2.6 probes are located at the rear of the outer bypass duct.

1.3 T6 Harness

The T6 harness consists of an insulated wiring harness and six individual thermocouples. The thermocouples are located at the leading edge of the exhaust case struts.

1.4 Variable Resistor

The resistor is mounted at the T6/T1 harness junction at the rear of the engine.




1.5 Operation

Simulated interturbine temperature (T5) readout is computed by adding three times the air temperature rise across the bypass duct to the exhaust temperature (JT15D-1 and 4 series).

Simulated interturbine temperature (T5) readout is computed by adding three times the air temperature rise across the fan to the exhaust temperature (JT15D-5 series). The resulting

signal is then corrected for sampling error with a variable resistor. By sensing the inlet and outlet temperatures of the bypass air stream, rise in air temperature through the bypass duct can be established by subtracting inlet from outlet temperature. This is accomplished via the T2 and T2.6 probes as each probe contains three thermocouples connected in series. Rise in temperature is multiplied by three to provide the required readout. The T6 probes are connected in parallel through the wiring harness to provide an average exhaust temperature. The T6 and T1 harnesses connected in series provide the output signal to the cockpit gauge. The simulated T5 temperature is represented by the following formula: T5 = T6 + 3 x (T2.6 - T2)




2 T5 SYSTEM CALIBRATION

2.1 Purpose

Adjust the indication in order to get a true representation of the engine temperature (correct for sampling errors).

2.2 Operation

Uneven heat distribution within the gas path causes individual thermocouple to sense different temperatures and generate different voltages (temperature). The actual temperature is calculated at engine test and is used to determine engine acceptance. A variable resistor mounted on the T1 harness corrects the untrimmed indication in order to send a valid engine temperature to the cockpit. The amount of trimming provided by the variable resistor is a function of its internal resistance. The resistance is set at engine test to generate the required temperature trim. The trim value in ohm is indicated on the engine trim data plate.




2.3 Maintenance

2.3.1 Loop resistance

Disconnect all leads from T1 harness connector on the inlet case

Measure loop resistance of T5 system between alumel and chromel terminals

Refer to Engine Maintenance Manual for resistance limits

2.3.2 Insulation resistance

Connect test set to alumel or chromel terminal and ground

Measure insulation resistance (5000 ohms minimum)

2.3.3 Heat response

Connect test set to alumel and chromel leads on the T6 harness

Heat each probe individually and verify for a response

If the variable resistor is found defective, replace the unit with new one and adjust it to the value marked on the engine plate

NOTE: Always clean connectors carefully to

ensure the system resistance is not disturbed. Repair the terminal post if the ceramic insulation is cracked. Individual probes, T1 and T6 harness can be replaced if found defective




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JT15D ATA 77