What is that thing inside the inlet cowl that is protrude out?

That is the T12 sensor inside the engine inlet cowl that is protrude out and its purpose is to send engine inlet temperature to the FADEC for fuel calculations and control. 

FADEC :- A full authority digital engine (or electronics) control (FADEC) is a system consisting of a digital computer, called an electronic engine controller (EEC) or engine control unit (ECU), and its related accessories that control all aspects of aircraft engine performance.

The T stands for temperature and 12 represents the station number of the engine in which the sensor is located.

That’s reason it called T12 sensor.


T12 sensor consists of two platinum sensing elements that receive a constant voltage from the EEC. In the elements, the current temperature resistance is proportional to the air temperature, where after the signal is send back to the EEC. The EEC now measures the difference between the output voltage and input voltage, which in turn is converted into a Fan Inlet Temperature.

The sensing element is a thermo resistive sensor that changes in resistance according to temperature. The forward slot is designed to help deflect any FOD that may damage the sensing element and also help remove/deflect water so that the sensing element receives a better temperature reading. The aft slot is where the sensing element is located and where the air exits. 


On the ground and up to 5 minutes after take-off EECs normally use T12 probe to calculate TAT(Total Air Temperature). This is to prevent temperature errors from the heated ADIRU (Air Data Inertial Reference Unit) TAT at slow speeds. 5 minutes after take-off EECs normally switch to ADIRU TAT probe for the two engines to use the same TAT value.Airplanes equipped with aspirated ADIRU TAT probes, EECs still use T12 on the ground and 5 minutes after take-off


The actual function of this sensor is to supply Total Air Temperature data in the Fan Inlet to the EEC which uses this TAT data for

  • Fuel requirement (Thrust) calculations
  • Positioning the Variable Bleed Valves
  • Positioning the Variable Stator Vanes
  • Low Pressure Turbine Active Clearance Control

After five minutes in the air the EEC compares four TAT signals:

  1. T12 from the active EEC channel
  2. T12 from the standby EEC channel
  3. Total air temperature from ADIRU 1
  4. Total air temperature from ADIRU 2

If all four signals are valid and in limits, the total air temperature from the ADIRU’s are used for the previous described operating functions. The EEC uses the ADIRU temperature before it uses the engine T12 sensor temperature so that both engines use the same value for TAT when possible. If both ADIRU temperatures are not valid, the EEC uses the T12 values for TAT input.


The T12 sensor is extremely reliable but if it were to fail or both engines have a disagreement on engine inlet temperature, the TAT probe would then send the information via the ADIRU (air data inertial reference unit) for temperature calculations.

Author: TECH SINGH Urs


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