POWER - DESCRIPTION AND OPERATION

** ON A/C NOT FOR ALL

1. General
This chapter deals with the N1, N2 indications.

** ON A/C NOT FOR ALL

2. N1 Indicating System

A. General
The measurement channel for the low pressure rotor is designed as follows:

the speed sensor on the engine sends a signal to the ECU
the ECU processes the N1 signal and transmits it to the ECAM through the ARINC 429 data bus (Ref. AMM D/O 73-25-00-00).

B. N1 Speed Sensor

(1) General
The N1 speed sensor is installed in the fan frame strut No.6 at the 5:00 o'clock position. It is secured to the fan frame with 2 bolts.
When the N1 speed sensor is installed on the engine you can only see these components :

the three-connector receptacle
the connector head
the sensor flange.

(2) Description

N1 Speed Sensor ** ON A/C NOT FOR ALL

The N1 speed sensor consists of the following:

a three-connector receptacle (channel A of the ECU - Engine Vibration Monitoring Unit - channel B of the ECU)
a flange for attachment of the sensor to the engine
a rigid metal tube including:
. two bonded damping rings,
. a magnetic head (sensor probe) which includes 3 windings, 3 permanent magnets and the pole pieces and three pairs of shielded lead wire providing the electrical signals from the sensing elements to the connectors.

(3) Operation

(a) Function

N1 Sensor Electrical Diagram ** ON A/C NOT FOR ALL

The N1 speed sensor:

detects the low pressure assembly rotational speed
transmits the corresponding signals to
. the Engine Vibration Monitoring Unit,
. the Electronic Control Unit, Channel 1 and
. the Electronic Control Unit, Channel 2.

(b) Principle
This sensor is an induction type tachometer. It consists of 3 independent sensing elements which are magnetically and electrically insulated from each other. Each sensing element includes a magnet, a winding, and a pole piece.
These sensing elements are hermetically enclosed in a stainless steel housing.
The sensitive elements transmit signals. The signals are supplied to the connectors through conductors embedded in a metal tube.
A sensor ring mounted on the fan shaft is provided with 30 teeth.
The passage of each tooth modifies the flux field of the magnets and causes a flux variation in the coils. This generates an alternating electromotive force proportional to the rotational speed of the low pressure rotor assembly.

NOTE: The sensor ring has one tooth thicker than the 29 others. This tooth generates a signal of greater amplitude used as phase reference for trim balance (processed in the EVMU).

C. N1 Indication

Upper Display Unit of the ECAM System - N1 Indication ** ON A/C NOT FOR ALL

The N1 indication is displayed on the upper display unit of the ECAM system :

in the analog form, by a pointer deflecting in front of a dial,
in the digital form, in the lower section of the dial.

The indication is normally green.
When N1 LIM < N1 < 102 percent :

the indication becomes amber

When N1 > 102 percent :

the indication becomes red
the MASTER CAUT light comes on accompanied by a single chime
the following messages appear on the ECAM :
- ENG 1(2) N1 OVERLIMIT
- THR LEVER 1(2)...BELOW LIMIT

If N1 has exceeded 102 percent :

the maximum value reached is memorized
a small red line remains positioned on the analog scale at that value (max pointer).
Above 103.8 percent the messages displayed on the ECAM becomes:
- ENG 1(2) N1 OVERLIMIT
- THR LEVER 1(2)...IDLE
- ENG MASTER 1(2)...OFF

N1 LIM
Value and modes appear in green (modes are CL, MCT, FLX TO, GA)
in FLX TO, the selected fictitious temperature is displayed in green.

N1 MAX

a small amber line positioned across the N1 analog scale at the value corresponding to that of the TO/GA mode.

N1 THR

a small white circle the shape of which recalls that of the throttle. This indication signals the predictive N1 value at which the engine LP rotor speed will stabilize for the given throttle position.

N1 CMD

a small arc in cyan colour linking the N1 actual value to the N1 CMD. This is displayed only with the autothrottle engaged. When the engine speed is stable, N1 actual = N1 CMD and the N1 CMD indication is not visible.

** ON A/C NOT FOR ALL

3. N2 Indicating System

A. General
The measurement channel for the high pressure rotor speed is designed as follows:

a speed sensor installed on the engine sends a signal to the ECU
the ECU processes the N2 signal and transmits it to the ECAM through the ARINC 429 data bus (Ref. AMM D/O 73-25-00-00).

B. N2 Speed Sensor

(1) General
The N2 speed sensor is installed at 6:30 o'clock on the accessory gearbox (AGB) rear face with 2 bolts.
When the sensor is installed, only the 3 fixed connectors and sensor body are visible.

(2) Description

N2 Speed Sensor ** ON A/C NOT FOR ALL

The N2 speed sensor consists of the following:
A body including:

three fixed connectors
a flange for attachment to the AGB
a groove which accommodates a seal for tightness between sensor and AGB.

A metal rigid tube including a magnetic head equipped with 3 polar pieces.

(3) Operation

N2 Sensor Electrical Diagram ** ON A/C NOT FOR ALL

The N2 speed sensor detects the rotational speed of the HP rotor assembly. It transmits the signal to the following equipment:

Engine Vibration Monitoring Unit (EVMU)
ECU (channel A)
ECU (channel B).

This sensor is an induction tachometer type. It comprises 3 sensitive elements. Each element is magnetically and electrically isolated from the other.
Each sensitive element includes a magnet, a coil and a polar mass. These sensitive elements are hermetically sealed in a stainless steel housing.
The sensitive elements transmit signals. The signals are supplied to the 3 connectors through resin embedded wires.
A magnetic wheel, part of the AGB drive system, is provided with 71 teeth on its web. The passage of each tooth in front of the magnetic head modifies the lines of magnetic force of the magnets. This creates a flux variation in the coils.
The flux variation generates an alternating electromotive force proportional to the rotational speed of the HP rotor assembly.

C. N2 Indication

Upper Display Unit of the ECAM System - N2 Indication ** ON A/C NOT FOR ALL

The N2 indication is displayed on the upper display unit of the ECAM system. The N2 indication is provided in the digital form.
The indication is normally green
When N2 > 105 percent:

the indication becomes red
the MASTER CAUT light comes on accompanied by a single chime
the following message appears on the ECAM:
- ENG 1(2) N2 OVERLIMIT
- THR LEVER 1(2)...BELOW LIMIT.
When N2 > 105.8 percent:
The indication and the MASTER CAUT light and single chime remain as above but the ECAM message becomes:
- ENG 1(2) N2 OVERLIMIT
- THR LEVER 1(2)...IDLE
- ENG MASTER 1(2)...OFF.
If N2 has exceeded 105 percent:
a red cross adjacent to N2 indication appears and remains during all the flight.

[Rev.10 from 2021] 2026.04.01 13:05:31 UTC