GPWS is a system that provides the Visual and Aural warning to the pilot if A/c is flying dangerously close to the Ground Proximity situations, to prevent a collision.
It has a Central Processing Unit which receives information from various Equipments and generates Audio and Visual warning through a Supervisor called Master Indicator.
The input are takes from the following –
- Radio Altimeter
- Vertical Speed Indicator
- Glide Slope of ILS
- Landing Gear position
- Flaps Position
These inputs are taken from these equipments and are used by the Central Processing Equipment to calculate the A/c maneuver by its logic system.
For Example- if A/c is below a specified altitude that provides adequate clearance from the terrain as fed in the GPWS, with the Landing Gear in up position. The Logic control Unit senses this abnormality an sends a signal to the Central Processing Unit that something is wrong, which generates the alert in the form of Aural alert like “Too Low Gear Up”, “Whoop Whoop – Pull Up” and Visual Alert like “A Flashing Light (Usually red in color) located in the Cockpit” to avoid A/c collision.
It also has a BITE (BUILT IN TEST EQUIPMENT) system, which when presses gives Audio and Visual Indications same as that the A/c gets while in close Proximity to the Ground, confirming that the equipment is operating normal.
BITE (Built in Test Equipment) in GPWS can not be used in flight.
Error- It cannot detect the steep cliff or high rising terrain, since the equipments works on the down looking principle and does not look forward as in the case of DME, Therefore no warning will be provided for a steep rising terrain.
It can provide adequate warning only for a gradually rising terrain, to prevent collision.
| MODE | FLIGHT CONDITIONS | WARNING RANGE | AURAL ALERT | WARNING IN THE COCKPIT |
| 1 | HIGH RATE OF DESCENT WITH RESPECT TO TERRAIN | 50- 2450 FEET | SINK RATE | WHOOP WHOOP PULL UP + FLASHING LIGHT |
| 2A | TOO FAST TERRAIN CLOSURE, A/C NOT IN LANDING CONFIGURATION | 50-1800 FEET | TERRAIN, TERRAIN | WHOOP WHOOP PULL UP + FLASHING LIGHT |
| 2B | TOO FAST TERRAIN CLOSURE, A/C IN LANDING CONFIGURATION | 220-790 FEET | TERRAIN, TERRAIN | WHOOP WHOOP PULL UP + FLASHING LIGHT |
| 3 | NEGATIVE CLIMB AFTER TAKE OFF | 50-700 FEET | DON’T SINK | ——— |
| 4A | UNSAFE TERRAIN CLEARANCE | 50-500 FEET | TOO LOW, GEAR UP | WHOOP WHOOP PULL UP + FLASHING LIGHT |
| 5 | EXCESSIVE GLIDE SLOPE DEVIATION ON ILS | 100-500 FEET | GLIDESLOP | ——— |
| 6 | DESCENT BELOW MINIMUMS | ——— | MINIMUMS | ——— |
WINDSHEAR DETECTION AND RECOVERY GUIDANCE SYSTEM-
Wind Shear is detected from a comparison between the rate of change of ground speed (measured by the Accelerometers located on the A/c) and the rate of change of the airspeed (measured by the ASI, through Pitot and Static)
SHEAR WARNING comes as a Red Flashing Warning Light in the Cockpit with Audio warning “WINDSHEAR WINDSHEAR”.
Recovery Guidance is based upon the angle of attack modified by the Radio Altitude, which measures the height of the A/c above the terrain, and pitch attitude which is displayed via the Flight Director, through the Attitude Director Indicator or on the EFIS display.