GROUND PROXIMITY GROUND PROXIMITY WARNING SYSTEMWARNING SYSTEM

GPWSGPWS

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

254 killed (Aug. 6, 1997) GPWS equipped254 killed (Aug. 6, 1997) GPWS equipped

Realvideo animation of Flight 801 descent

CFITCFIT

• Controlled flight into terrain.• Prior to the widespread implementation of

GPWS, CFIT was an all too common occurrence.

• CFIT accidents involve a normally operating aircraft which contacts the ground due to loss of situational awareness, or other pilot error.

• GPWS has greatly reduced the number of these incidents.

GPWSGPWS

• GPWS is a system developed to help prevent CFIT accidents.

• In the event of a loss of situational awareness by the crew GPWS is a last resort lifeline to warn of approaching terrain.

• The pilots are alerted through aural and visual warnings and in the case of EGPWS a visual display.

HOW IT WORKSHOW IT WORKS

• The heart of the GPWS is a computer processor which interprets data from a number of sources:– Radar altimeter– Air data computer– UHF Nav receiver– Gear and flap indicating system– Roll attitude input sensor

HOW IT WORKSHOW IT WORKS

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

• If the aircraft is in landing configuration at approach speed and approaching the ground it is deemed a warning is unnecessary.

AURAL WARNINGSAURAL WARNINGS

• Some typical GPWS warnings are:– “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 annunciator.

• In the event of a “PULL UP” warning a recovery procedure must be initiated.

MODE 1MODE 1

• Warns of excessive descent rate.

• If the aircraft is less than 2500AGL, as determined by the radar altimeter, and is losing altitude too quickly.

• 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.

MODE 2MODE 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.

MODE 3MODE 3

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

• Within the first 1000 AGL if the aircraft starts to sink rather than climb.

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

MODE 4MODE 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.

MODE 5MODE 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.

RECOVERY PROCEDURERECOVERY 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.

• NOTE: in VMC conditions terrain may be avoided visually.

ADVISORY CALLOUTSADVISORY CALLOUTS

• GPWS is capable of advisory callouts as an aid to normal operations:– “GLIDESLOPE” two dots below glideslope– “FIVE HUNDRED” 500 AGL on non-precision

approach– “MINIMUMS, MINIMUMS” upon reaching

radar altimeter selected decision height.

EGPWSEGPWS

• 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.

• 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.