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Lecture 9:Ground Proximity
Warning System (GPWS)
By: Zuliana Ismail,2010
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What is GPWS?
• A Ground Proximity Warning System (GPWS) is a type of equipment carried by aircraft to warn pilots if they are at a dangerously low altitude and in danger of crashing.
The pilots are alerted through visual and audio warnings by GPWS display inside cockpit.
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Purpose of GPWS
• The main purpose of these systems is to prevent what is called a Controlled Flight Into Terrain (CFIT)
• CFIT is an accident in which an aircraft crashes into the ground, the water, or an obstacle such as a mountain or building .
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CFIT= Controlled Flight Into Terrain
Since 1960s, a series of Controlled Flight Into Terrain (CFIT) accidents killed hundreds of people.
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CFIT and GPWS
• CFIT can be the result of factors such as navigation errors, pilot fatigue, or reduced visibility owing to weather conditions.
• CFIT incidents have been reduced since GPWS entered widespread use in the 1970s.
• The use of a GPWS in large aircraft is required by law in many countries.
• In the late 1990s improvements were made and the system was renamed "Enhanced Ground Proximity Warning System“ (EGPWS)
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How GPWS Works?• RA measures how far
aircraft from the ground.
• GPWS computer analyzed the information from radar.
• Computer can identify hazardous situations (very close to ground/terrain, rapid ROD & loss of altitude)
• GPWS display gives visual and audio warning signals to the pilot.
(RA)
Visual Audio
What is the different between radar altimeter and barometric altimeter?
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How GPWS Works?
• A GPWS monitors the aircraft's altitude with a Radar Altimeter, which transmits radio waves downward from the plane to determine how far away the ground is.
• Most radar altimeters carried by commercial aircraft are short-range devices with ranges of less than a mile (about 1.6 km).
• The information from the radar is monitored and analyzed by a computer that can identify hazardous situations and trends in the data, such as
– a dangerously rapid rate of descent,
– dangerously close ground during, or
– unexpected loss of altitude.
• If hazardous conditions are detected, the GPWS gives visual and audio warning signals to the pilot.
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Radar Altimeter Vs Barometric Altimeter
What is the different between radar altimeter and barometric altimeter?
• A Radar Altimeter (RA) measures the distance between the plane and the ground directly below it.
• Barometric altimeter provides the distance above sea level.
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Audio & Visual Warning
• Audio & 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”)
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GPWS ModesMODE WARNING
Mode 1: Excessive Descent Rate.
when Rate of Descent(ROD) increase
rapidly
“sink rate, sink rate”
“whoop, whoop, pull up, pull up”
Mode 2: Excessive Terrain Closure
Rate
when closure rate with terrain is too high.
“terrain, terrain”
“whoop, whoop, pull up, pull up”
Mode 3: Descent after take-off
warn loss of altitude after take-off.
“don’t sink”
Mode 4: Unsafe Terrain Clearance
Too low, landing gear/flap configuration.
“too low, terrain”“too low, gear” too low, flaps”
Mode 5: Descent below Glide Slope
Too low “Glideslope”
Mode 6: Situation Awareness Bank Angle, Altitude “Minimums”“Bank Angle”
Mode 7: Wind shear Information “Wind Shear”
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MODE 1: Excessive Descent Rate..
• Warns of excessive Rate of Descent(ROD)
• 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: Excessive Terrain Closure Rate
• 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.• Recovery: Continue climb until clear of terrain.
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MODE 3: Altitude Loss After Take-off
• Warns of loss of altitude after take-off.
• If the aircraft sinks 10 percent of its radar altitude “don’t sink” will be heard.
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MODE 4: Unsafe Terrain Clearance
• Terrain clearance while aircraft take-off, climb, cruise, and descent.– If the airspeed is higher the warning will be “too low, terrain”
• Alert the configuration of landing gear during approach.– if the aircraft is too low and slow, with landing gear retracted
(not open).
– “too low, gear”
• Alert the configuration of flaps during landing– When the gear is selected down, but the flaps are still retracted
(not open)
– “too low, flaps”
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Mode 5, 6, 7
• Mode 5: Descent below Glide Slope
• Mode 6: Situation Awareness (Bank Angle, Altitude)
• Mode 7: Wind shear Information