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GROUND PROXIMITY WARNING SYSTEM

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GROUND PROXIMITY WARNING SYSTEM

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    1. GROUND PROXIMITY WARNING SYSTEM GPWS

    2. Korean Airlines Boeing 747 CFIT while attempting to land in heavy rain: 228 of 254 killed (Aug. 6, 1997) GPWS equipped

    3. Realvideo animation of Flight 801 descent

    4. 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.

    5. 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.

    6. 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

    7. 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.

    9. AURAL 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.

    10. 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.

    11. 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.

    12. 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 “don’t sink” will be heard.

    13. 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.

    14. 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.

    15. 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.

    16. 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.

    17. 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.

    18. 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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