Lecture 9: Ground Proximity Warning System (GPWS)

Home Previous Next Help Ground Proximity Warning System (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 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.

Home Previous Next Help CCFIT= Controlled Flight Into Terrain Since 1960s, a series of Controlled Flight Into Terrain (CFIT) accidents killed hundreds of people.

Home Previous Next Help CFIT and GPWS CFIT can be the result of factors such as navigation errors, pilot fatigue or disorientation, 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)

Home Previous Next Help Ground Proximity Warning System (GPWS) 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.

Home Previous Next Help Radar Altimeter A radar altimeter or simply RA measures altitude above the terrain presently beneath an aircraft. This type of altimeter provides the distance between the plane and the ground directly below it, as opposed to a barometric altimeter which provides the distance above sea level.

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 & Navigation Antennas –Gear and flap indicating system –Roll attitude input sensor The computer analyzes a number of parameters such as, speed, proximity to terrain, and descent rate in order to issue appropriate warnings. The pilots are alerted through visual and audio warnings by GPWS display inside cockpit.

Home Previous Next Help 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”)

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 GPWS Modes Mode 1: Excessive Descent Rate.. Mode 2: Excessive Terrain Closure Rate Mode 3: Altitude Loss After Take-off Mode 4: Unsafe Terrain Clearance

Home Previous Next Help MODE 1: Excessive Descent Rate.. 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: 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.

Home Previous Next Help MODE 3: Altitude Loss After Take-off 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: Unsafe Terrain Clearance 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 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 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.

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Home Previous Next Help Question 2: FAA defines GPWS as a type of ________. a)Terrain awareness and warning system b)Aircraft flight control system c)Controlled flight into terrain d)Ground proximity warning system

Home Previous Next Help Question 3: ________ a)American Airlines Flight 191 b)Antarctica1979 c)Garuda Fokker F28 crash d)Air New Zealand Flight 901

Home Previous Next Help TACA Flight 390Santa Bárbara Airlines Flight 518Continental Airlines Flight 1404Hewa Bora Airways Flight 122

Home Previous Next Help In the late 1990s improvements were made and the system was renamed "Enhanced Ground Proximity Warning System" (________/TAWS). a)Global Positioning System b)Local Area Augmentation System c)Ground proximity warning system d)Global navigation satellite system

Home Previous Next Help Question 6: The system was now combined with a worldwide digital terrain database and relies on Global Positioning System (________) technology. Compass Inertial navigation system Global Positioning System F-15 Eagle