CONTENTS
Amendment: Note regarding Look-Ahead Terrain Alerting positional inputs.
The Ground Proximity Warning System (GPWS) provides alerts for potentially hazardous flight conditions involving imminent impact with the ground.
Ground proximity time critical warnings are accompanied by master WARNING light illumination and voice aural alerts. Ground proximity cautions are accompanied by ground proximity light illumination and a voice aural alert.
If illuminated, pushing a master warning/caution reset switch resets the master WARNING lights but does not deactivate the ground proximity warning.
Aural cautions are accompanied by ground proximity light illumination. The master CAUTION lights do not illuminate for ground proximity cautions.
Note: Terrain ahead of the airplane may exceed available climb performance. A ground proximity caution or warning does not guarantee terrain clearance.
Note: The GPWS does not provide an alert for flight toward vertically sheer terrain or slow descents into terrain while in the landing configuration.
The GPWS requires inputs from the following systems for proper operation:
In addition, the terrain awareness alerting and terrain display functions [Look-Ahead Terrain Alerting] require inputs from the:
Note: Loss of an input does not necessarily inhibit operation of the entire GPWS.
Notes:
The GPWS provides alerts based on radio altitude and combinations of barometric altitude, airspeed, glide slope deviation, and airplane configuration and is operative between 30 ft and 2450 ft RA. The alerts are for:
These alerts are "radio altitude based alerts".
Radio altitude based alerts are prioritised based on the level of hazard and the required flight crew reaction time.
As installed Radio altitude based alerts are inhibited by an actual windshear warning (airplane in windshear).
Master WARNING lights.As installed - Red PULL UP message on both ADIs.
Follows SINK RATE alert if descent rate lights becomes severe.
Follows radio altitude based TERRAIN alert if excessive terrain closure rate continues and landing gear and/or flaps are not in landing configuration.
The height of the floor of the Mode 2B envelope will vary between 200 and 600 feet radio altitude based on barometric descent rate. This provides additional protection against nuisance alerts during approaches where the runway threshold is in close proximity to rising terrain, as in the case of an airport on a plateau.
Follows DON'T SINK if another descent is initiated after initial alert, before climbing to the altitude where the initial descent began.
Unsafe terrain clearance at low airspeed with landing gear not down.
Pushing the ground proximity GEAR override switch to OVRD inhibits the alert.
Unsafe terrain clearance at high airspeed with either landing gear not down or flaps not in landing position.
Unsafe terrain clearance at low airspeed with flaps not in landing configuration.
Pushing the ground proximity FLAP override switch to OVRD inhibits the alert.
The mode is armed when a valid signal is being received by the left glide slope receiver, the radio altitude is 1000 feet or less and the landing gear is down.
Deviation of more than 1.3 dots below glide slope. Volume and repetition rate increase as deviation increases.
Pushing the ground proximity G/S INHB switch cancels or inhibits the alert below 1,000 feet radio altitude.
The mode rearms when climbing above 1000 feet radio altitude or descending below 30 feet radio altitude.
TCX Although some manufacturers of GPWS equipment may show in their literature TOO LOW TERRAIN to be an alert, Company procedure [dictates] that the response is as for a warning.
As installed The GPWS monitors terrain proximity using an internal worldwide terrain database. Proximate terrain data shows on the HSI. If there is a potential terrain conflict, alerts are provided based on estimated time to impact. These alerts are "look-ahead terrain alerts".
The GPWS terrain database contains detailed terrain data near major airports, and data in lesser detail for areas between airports. Terrain within 2,000 feet of airplane barometric altitude shows on the navigation display. The terrain data is not designed to be an independent navigation aid.
Note: The GPWS terrain database, look-ahead terrain alerting, and terrain display do not account for man made obstructions. Where such information is available in the data base, the warnings OBSTACLE PULL UP and CAUTION OBSTACLE can be generated.
Although the terrain display is generated using a built in sweep, the display is not a radar display; the terrain display is computer-generated from a database contained in the GPWS computer and correlated to GPS position. Terrain Alerting and Display is not available in areas without terrain data.
Terrain and Weather Radar cannot show together on a display. If one pilot selects terrain and the other pilot selects weather radar, each display updates on alternating sweeps. All other displays (TCAS, LNAV routing, etc.) can show with terrain data.
Look-ahead terrain alerts are based on the airplane's position, barometric altitude, vertical flight path, and ground speed.
Look-ahead terrain alerts are prioritised based on the level of hazard and the required flight crew reaction time. Look-ahead terrain alerts are inhibited by an actual windshear warning (airplane in windshear).
Red PULL UP message on both ADIs.
Master WARNING lights.
Red TERRAIN message on HSI (all modes).
Solid red terrain on HSI
20 to 30 seconds from projected impact with terrain shown solid red on the HSI (in MAP, CTR MAP, VOR, or ILS modes only).
Pushing the ground proximity terrain override switch to OVRD inhibits the alert.
Amber TERRAIN message on HSI (all modes)
Solid amber terrain on HSI.
GND PROX light
40 to 60 seconds from projected impact with terrain shown solid amber on the HSI (in MAP, CTR MAP, VOR, or APP modes only).
Descent below unsafe radio altitude while too far from any airport in the terrain database.
Note: In areas without terrain data, look ahead terrain alerting and terrain display functions not available. Radio altitude based terrain alerts function normally.
Note: Terrain more than 2,000 feet below airplane altitude or within 400 feet of nearest airport runway elevation does not show. (see Peaks Display Mode)
Automatically shows when:
Updates with a display sweep, similar to weather radar display.
As installed An enhancement to the current "standard" EGPWS terrain display, the Peaks Mode terrain display, allows terrain below the aircraft to be viewed on the HSI during the cruise portion of flight. At altitudes safely above all terrain for the display range chosen, the terrain is displayed independent of aircraft altitude emphasising the highest and lowest elevations to provide increased situational awareness. This increased awareness can be particularly valuable to the flight crew in the event of an unplanned descent or off route deviation and for the purpose of previewing terrain prior to descent.
Previously, the standard GPWS/EGPWS terrain display used colours and shading patterns corresponding to the vertical displacement between terrain elevation and the current altitude of the aircraft. Terrain more than 2000 feet below the aircraft is not displayed and the terrain display is typically blank during the enroute portion of the flight. The Peaks Mode display is thus a "merged" display applicable to all phases of flight.
With the new Peaks Mode display, two elevation numbers indicating the highest and lowest terrain currently being displayed are overlaid on the display. The elevation numbers indicate terrain in hundreds of feet above sea level (MSL). The terrain elevation numbers are displayed with the "highest" terrain number on top, and the lowest terrain number beneath it. The "highest" terrain number is shown in the same colour as the highest terrain colour pattern on the display, and the "lowest" terrain number is shown in the colour of the lowest terrain colour pattern on the display. A single elevation number is displayed when the screen is all black or blue as a result of flying over water or relatively flat terrain where there is no appreciable difference in terrain elevations. The elevation numbers on the display are an additional indication that the terrain display is selected.
The background colour dot patterns and terrain elevation threshold values are shown in the following table:
(Bold Italics indicate new functionality in Peaks Mode)
The Peaks Mode display adds a new solid green level to indicate the highest, non-threatening terrain. The existing lower density green display patterns now indicate mid and upper terrain in the display area as well as terrain that is within 2000 feet below the aircraft. The red and Yellow dot patterns are unchanged and continue to indicate terrain that is near or above the current altitude of the aircraft. Solid Yellow and Red colours are unchanged and continue to indicate alert and warning areas relative to the aircraft flight path. Terrain identified as water (0 feet MSL) may optionally be displayed as cyan colour dot patterns if the aircraft display hardware supports the colour cyan. The Peaks Mode display is prioritised such that higher-level colours and densities override lower colour and densities for maximum situational awareness.
As installed GPWS provides voice alerts for terrain awareness and potentially unsafe flight conditions.
As installed GPWS provides a voice callout at selected radio altitudes to advise the flight crew of the approximate height above ground level. Voice callouts are provided at:
GPWS also provides a voice callout reaching decision height or minimum descent altitude set on the captain's radio altimeter:
(SB changes) GPWS provides a voice callout at selected bank angles to advise the flight crew when exceeding bank angle thresholds. A one cycle aural warning BANK ANGLE, BANK ANGLE sounds when roll angle exceeds 35 degrees, 40 degrees and 45 degrees. Once the warning sounds it will not sound again until roll angle decreases below 30 degrees and again exceeds 35 degrees.
As installed An aural alert is enabled as the airplane descends from decision height (DH) plus 75 feet to DH plus 50 feet. It is a pulsed tone that activates as the airplane passes through DH plus 50 feet and continues to DH. Also, the repetition rate of the tone increases as the airplane approaches DH. The tone is automatically turned off when the airplane descends below DH or climbs above DH plus 50 feet. The alert can be enabled again by climbing above DH plus 75 feet and then descending through DH plus 50 feet.
As installed A voice callout of FIFTY ABOVE occurs when the airplane reaches fifty feet prior to the decision height altitude set on the captain's radio altimeter. The voice callout DECIDE occurs at the decision height.
As installed Some airplanes have a 500 foot callout that sounds only when the airplane is not within ±2 dots of a valid ILS glide slope or valid ILS glide slope is not available. If the Mode 5 aural warning GLIDE SLOPE is active, the 500 foot callout will not sound unless the warning is cancelled with the Glide Slope Inhibit Switch.
Windshear