GROUND PROXIMITY WARNING SYSTEM

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GROUND PROXIMITY WARNING SYSTEM

• GPWS

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Korean Airlines Boeing 747 CFIT while attempting
to land in heavy rain 228 of 254 killed (Aug. 6,
1997) GPWS equipped
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• Realvideo animation of Flight 801 descent

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CFIT

• 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.

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GPWS

• 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.

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HOW 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

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HOW 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.

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AURAL WARNINGS

• Some typical GPWS warnings are
• SINK RATE
• TERRAIN, TERRAIN
• DONT 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.

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MODE 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.

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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.

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MODE 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 dont sink will be heard.

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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.

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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.

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

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ADVISORY 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.

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EGPWS

• 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.

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• 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.

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