Lecture 9 Ground Proximity Warning System (GPWS) Radio Aids & Navigational System

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.

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.

CFIT Controlled Flight Into Terrain Since 1960s, a series of Controlled Flight Into Terrain (CFIT) accidents killed hundreds of people.

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)

Visual Audio What is the different between radar altimeter and barometric altimeter?

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.

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. How GPWS Works?

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.

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”)

GPWS Modes MODEWARNING 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”

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.

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.

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.

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”

Mode 5, 6, 7  Mode 5: Descent below Glide Slope  Mode 6: Situation Awareness (Bank Angle, Altitude)  Mode 7: Wind shear Information