Message Name:

INTER TURBINE TEMPERATURE (ITT) LOW READING

Inter Turbine Temperature (ITT) Low Reading.

• Inter Turbine Temperature (ITT) Thermocouple Probe
• Associated Wiring

Advisory Wire/Service Bulletin: None

Full Throttle Blog/Forum Articles/Infoservice/Newsletter: None

Notice To Operator (NTO):

• NTO 087 Troubleshooting in case of ITT cross-check failure

Flight Operation Notifications Manual (FONM): None

WARNING: BE CAREFUL WHEN YOU DO WORK ON THE ENGINE DURING OR AFTER ENGINE OPERATION. THE ENGINE PARTS STAY HOT FOR APPROXIMATELY ONE HOUR AFTER THE ENGINE STOPS. THIS CAN CAUSE INJURY TO PERSONS.

WARNING: BE CAREFUL IF YOU MUST DO WORK ON HOT COMPONENTS. USE APPROVED GLOVES AND PROTECTIVE CLOTHING. IF YOU DO NOT DO THIS, YOU CAN CAUSE INJURY TO PERSONS.

1. With the engines running with matched N2/NH speed, identical electrical load and customer bleed demands, check for ITT split between engines on Engine Indication and Crew Alerting System (EICAS). Look for Engine Health Monitoring (EHM) advisory alerts for increased ITT margin.

   1. If EHM trend has reported 'Increased ITT margin', go to step 3.
   2. If 'Inter-Turbine Temperature (ITT) Split between Engines' is observed on EICAS, continue with next step.

2. Perform the troubleshooting for observed fault 'ITT split between engines' to determine whether ITT low reading is an indication issue or not.

   1. If NO, carry out the troubleshooting for the primary cause identified and do close out.
   2. If YES, continue with step 4.

3. Perform the operational test of the FADEC (TASK 73-21-00-710-801). Refer to the CAIMS PMAT general instructions when you use the CAIMS PMAT (AMM TASK 45-45-00-970-801).

   1. If the system checks are good, do close out.
   2. If fault remains, continue with next step.

4. On the CAIMS PMAT, get access to the maintenance alert messages and get access to the active faults (AMM TASK 45-45-00-970-802) and stored faults (AMM TASK 45-45-00-970-803). Look for the below error codes from the active and stored faults:

   Fault Code	Fault Message
   7325725LBR	L ITT SIGNAL FAULT (CHANNEL A)
   7325725RBR	R ITT SIGNAL FAULT (CHANNEL A)
   7325726LBR	L ITT SIGNAL FAULT (CHANNEL B)
   7325726RBR	R ITT SIGNAL FAULT (CHANNEL B)
   7325727LBR	L ITT SIGNAL WRG XCK
   7325727RBR	R ITT SIGNAL WRG XCK

   1. If any error code displayed, perform the applicable troubleshooting procedure and continue with next step.
   2. If no error code displayed, continue with next step.

5. Check if the troubleshooting resolves the issue or not.

   1. If the troubleshooting does not resolve the issue, proceed to fault isolation.
   2. If the troubleshooting resolves the issue, continue with next step.

6. Do close out.

Fault Isolation:

SUBTASK 77-21-00-810-YYY:

1. Get access to the core harness disconnect panel on Bypass Duct (BPD) (TASK 72-71-01-000-801).
2. Remove the plug P1030 and perform the resistance check as follows:

   From	To	Expected Result	Result
   P1030-16	Ground	1 Megaohm

   1. If resistance is more than 1 MΩ, Contact Rolls-Royce Deutschland (RRD).
   2. If resistance is less than 1 MΩ, continue with next step.

3. Do close out.

SUBTASK 77-21-00-810-ZZZ:

1. Get access to the ITT probes (TASK 72-03-02-000-801) and continuously measure the IR between Pin 16 on plug P1030 and ground whilst disconnecting one ITT probe after another from the ITT ladder harness.
2. Identify the ITT probe(s) that cause low system IR.
   NOTE: Start with the ITT probes installed in Top Dead Center (TDC).
3. Remove the affected ITT probes (TASK 77-21-01-000-801). Measure the Insulation Resistance (IR) between the terminal stud and ground (probe housing).
   NOTE: Record the IR values in the table format as shown in Fig. 77-21-00-YYY-YYY.
   NOTE: The ITT probe insulator might show contamination as shown in Fig. 77-21-00-XXX-XXX.
4. Blast clean the ITT probe insulator (refer to the ITT Thermocouple Components Maintenance Manual (CMM 77-21-23, Page 401).
   NOTE: If on-site blast cleaning is not possible and the probe S/N is readable, return ITT probes with contaminated ceramic insulator to supplier for repair. Otherwise, scrap the part locally.
5. Measure the Insulation Resistance (IR) between the terminal stud and ground (probe housing).

   1. If IR is more than 20 MΩ, reinstall ITT probe (TASK 77-21-02-400-801).
   2. If IR is less than 20 MΩ, reject the ITT probe.

6. Perform the repair confirmation after every unit replacement/repair.
7. Do close out.

SUBTASK 77-21-00-710-ZZZ:

1. Perform the steps that follow to find out if the repair was satisfactory.
2. Start the left and the right engine (TASK 71-00-00-860-809). Stabilize the engines at idle, match the N2/NH speeds and wait until the ITT indication is steady.
3. Get access to the OMS (Refer to Aircraft Maintenance Manual (AMM)). Look for ITT related maintenance messages, dashed #### ITT indication during engine operation.

   • Look at the Fault Maintenance pages and make a selection of the Currently Active Faults
   • Look for the ITT related error codes, if active, do the associated Fault Isolation procedure

   1. If ITT related error codes do not show and the suspect engine ITT is not reading low, you have corrected the fault.

4. Stop the engines (TASK 71-00-00-860-810).
5. Do close out.