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Inertial Reference System(IRS)

The inertial reference system (IRS) provides inertial navigation data to user systems. It uses a ring laser gyro instead of the conventional rate gyro to sense angular rate about the roll, pitch and yaw axes. The system is termed strap down since its sensors are, in effect, directly mounted to the airframe.

Inertial Reference System(IRS)

Operation of Inertial Reference System(IRS)

- Inertial reference unit (IRU) provides attitude, acceleration, angular rates, velocity, true and magnetic headings, positional data, absolute altitude and wind data signals.

- The signals are developed from a set of three laser gyros and three accelerometers mounted to airplane reference.

- The IRS provides basic heading and attitude reference accomplished through computations based on accelerometer and laser gyro sensed signals.

- Three accelerometers and three laser gyros are used.

- The first requirement which must be met for proper IRS operation is alignment.

Inertial System Display Unit(ISDU)

- It provides pilot interface with the IRUs.

- It also allows entry of initialization data for the IRU's.

- The display of track angle, ground speed, present position, wind direction and speed, heading and system status is available.

Mode select unit(MSU)

Inertial Reference System(IRS)

Mode select unit (MSU) provides mode selection for two IRU's through two mode select switches and monitors the operation of the IRU's through two sets of alert lights mounted on the unit.

The inertial reference system (IRS) includes,

- Inertial reference units (IRU),

- Inertial system display unit (ISDU),

- Mode select unit (MSU)

Ground proximity warning system

Different modes of Ground Proximity Warning System

IRS Mode of Operation

- Ground Proximity Warning System (GPWS) is a system designed to alert pilots if their aircraft is in immediate danger of flying into the ground or an obstacle.

- Another common name for such a system is Ground-Collision Warning System (GCWS).

IRS Alignment

- IRS alignment consists of determining local vertical and initial heading.

- Both accelerometer and laser gyro inputs are used for alignment.

- The alignment computations use the basic premise that the only accelerations during alignment are due to the earth's gravity.

Navigate Mode

- In the navigate mode the IRUs provide outputs for attitude, heading, present position, accelerations, track angle, drift angle, ground speed, and wind data.

- The initial attitude, heading and velocity signals are modified by inputs from the sensors to establish real time present parameters through integration and computer calculations.

- Mode 1: Excessive Descent Rate - Provides 'Sink rate!' and 'Pull up!' alerts based on descent rate at low radio altitudes (below 2500').

- Mode 2: Excessive Terrain Closure Rate - Provides 'Pull up!' and 'Terrain!' callouts around rising terrain.

- Mode 3: Altitude Loss After Takeoff - Provides alerts against altitude loss after takeoff (or a go-around). Losing altitude triggers a 'Don't sink!' alert.

- Mode 4: Unsafe Terrain Clearance - Provides alerts against insufficient clearance, based upon the aircraft configuration and flight phase (takeoff, cruise, approach), and independent of terrain closure rate (i.e situations that modes 1 & 2 would not alert).

- Mode 5: Excessive Deviation Below Glideslope - Provides 'Glideslope!' alerts when deviating below a glideslope while established on a localizer.

- Mode 6: Advisory Callouts - Provides callouts based on the specified decision-height and radio altitude. It also provides a 'Bank angle' alert based upon excessive aircraft roll.

- Mode 7: Windshear Protection - Windshear protection is currently not implemented.

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