Lecture 9:Ground Proximity

Warning System (GPWS)

Home

Previous

Next

Help

Ground Proximity Warning System (GPWS)

• Since 1960s, a series of Controlled Flight Into Terrain (CFIT) accidents killed hundreds of people.

• Thus, a device called a ground proximity warning system (GPWS) had been used to overcome CFIT problem.

Home

Previous

Next

Help

Controlled Flight Into Terrain

• CFIT describes about aircraft collision, under pilot control, inadvertently flies into terrain, an obstacle, or water.

• The pilots are generally unaware of the danger until it is too late.

Home

Previous

Next

Help

Korean Airlines Boeing 747: CFIT while attempting to land in heavy rain: 228 of 254

killed (Aug. 6, 1997)

Home

Previous

Next

Help

Ground Proximity Warning System (GPWS)

• A 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.

• GPWS has greatly reduced the number of CFIT incidents.

Home

Previous

Next

Help

HOW GPWS WORKS

• The heart of the GPWS is a computer processor which interprets data from a number of sources such as radar, gear and flap indicating system & roll attitude input sensor.

• The computer analyzes a number of parameters including aircraft configuration, speed, proximity to terrain, and descent rate in order to issue appropriate warnings.

• The pilots are alerted through aural & visual warnings by GPWS display inside cockpit.

Home

Previous

Next

Help

Aural & Visual Warning

• Aural & Visual Warnings are provided under any of the following conditions:

– Excessive rate of descend (“sink rate”)

– when closure rate with terrain is too high (“terrain-terrain”)

– loss of altitude after take-off (don’t sink)

– if the aircraft is too low and slow, with landing gear retracted (“too low, gear”)

Home

Previous

Next

Help

AURAL WARNINGS

• Some typical GPWS warnings are:– “DESCENT,DESCENT”– “CLIMB, CLIMB”– “SINK RATE”– “TERRAIN, TERRAIN”– “DON’T SINK”– “TOO LOW, TERRAIN”– “TOO LOW GEAR”– “PULL UP”

• These aural warnings will be accompanied by illumination of a GPWS display.

Home

Previous

Next

Help

MODE 1

• Warns of excessive descent rate..

• A GPWS warning light will illuminate and “sink rate, sink rate” will be heard.

• If the situation is not corrected “whoop, whoop, pull up, pull up” will be heard.

Home

Previous

Next

Help

MODE 2

• Warns crew when closure rate with terrain is too high.

• Designed to warn crew when rising terrain is a threat.

• “terrain, terrain”• “whoop, whoop, pull up, pull up”• There may be no change in barometric altitude

but the radar altitude is decreasing.

Home

Previous

Next

Help

MODE 3

• Warns of loss of altitude after take-off, or go-around.

• If the aircraft sinks 10 percent of its radar altitude “don’t sink” will be heard.

Home

Previous

Next

Help

MODE 4

• MODE 4a: if the aircraft is too low and slow, with landing gear retracted.

• “too low, gear”

• If the airspeed is higher the warning will be “too low, terrain”

• MODE 4b: When the gear is selected down, but the flaps are still retracted “too low, flaps”

• This warning can be canceled by the pilot in the event of a flapless landing.

Home

Previous

Next

Help

MODE 5

• Warns the crew of glideslope deviations.

• When the aircraft receives a valid glideslope and sinks two dots below “glideslope” will be heard.

• The warning will continue with increasing intensity if the problem is not corrected.

• This warning may be canceled by the pilot.

Home

Previous

Next

Help

RECOVERY PROCEDURE

• Recovery procedure will vary depending on the type of aircraft, but the general response is:– Roll level and simultaneously set maximum power.

– Slowly pitch up and maintain Vx.

– Retract gear and flaps.

– Continue climb until clear of terrain.

Home

Previous

Next

Help

Enhanced Ground Proximity Warning System

• Enhanced Ground Proximity Warning System• A limitation of GPWS is the fact that with radar

altimeter information only the aircraft is only capable of seeing terrain directly below.

• In the case of rapidly rising terrain it may not react quick enough to issue a warning in time.

Home

Previous

Next

Help

Enhanced Ground Proximity Warning System

• EGPWS corrects this problem by integrating an aircraft navigational source into the system.

• GPS position in conjunction with a terrain database is used to help predict terrain conflict.

• Any catalogued man made obstructions are included in the database.

• This type of system can be used to display terrain profile to the pilot to improve situational awareness.

Home

Previous

Next

Help