*
The ground proximity light.

This is the warning:
*
A red PULL-UP message on the PFDs

*
The master warning lights come on

*
An aural message PULL-UP.

The warning changes back to the alert annunciation TERRAIN and the ground proximity light on if the closure rate decreases or if the pilot does a pull up maneuver.
The alert annunciation continues until there is an increase of 300 feet inertial altitude or the gear comes down.
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777 AIRCRAFT MAINTENANCE MANUAL

GPWS -MODE 2A DESCRIPTION

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GPWS -MODE 2B DESCRIPTION

General
Mode 2B gives annunciations for a large closure rate when the flaps are down (more than 15 units).
Mode 2B gives two types of annunciations that depend on the position of the landing gear.
When the landing gear is down, the GPWC gives an alert. These are the annunciations:
*
The aural message TERRAIN TERRAIN

*
The ground proximity light comes on.

When the gear is up, the alert is a warning and these are the annunciations:
*
The aural message PULL-UP

*
Master warning lights come on

*
A red PULL-UP message on the PFDs.

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777 AIRCRAFT MAINTENANCE MANUAL

GPWS -MODE 2B DESCRIPTION

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GPWS -MODE 2 OPERATION

General
Mode 2A annunciations occur between 30 feet and 1650 feet. The upper limit goes up to 2450 feet for airspeeds more than 310 kts.
Mode 2B annunciations occur between 600 feet and 789 feet. The lower limit goes down to 200 feet for inertial vertical speed (IVS) rates less than 400 feet per minute.
The LRUs that supply inputs for mode 2 operation are the left, right, and center radio altimeter transceivers and the AIMS cabinets.
This is the data the GPWC uses to detect mode 2 alerts and warnings:
*
Radio altitude

*
Inertial vertical speed (IVS)

*
Barometric altitude rate

*
Barometric altitude

*
Computed airspeed

*
Flap and gear position.

Operation
The mode detector uses the inputs to find if there is an alert or warning condition.
If there is an alert condition, the detector sends a discrete to the ground proximity light. The discrete goes to the speech prom to enable the alert aural. The alert aural goes to the WES which sends it to the aural warning speakers in the flight deck.
The alert discrete also goes to the TCAS computer to inhibit any TCAS advisory messages.
If there is a warning condition, the mode detector sends a PULL-UP discrete to the AIMS cabinet to show the message on the PFDs. The AIMS cabinets send the discrete to the WES to turn on the master warning lights. The warning discrete goes to the speech prom to enable the warning aural. The warning aural goes to the WES which sends it to the aural warning speakers in the flight deck.
The ground proximity warning discrete goes to the TCAS computer to inhibit any TCAS advisory messages.
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777 AIRCRAFT MAINTENANCE MANUAL

GPWS -MODE 2 OPERATION

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GPWS -MODE 3 DESCRIPTION

Purpose
*
Ground proximity light Mode 3 supplies alerts for a large altitude loss during: * Aural message TOO LOW TERRAIN.

*
Takeoff

*
A missed approach when the gear is up and flaps are less
than 25 units.

Mode 3 consists of these two submodes:
*
Submode 3A

*
Submode 3B.

Submode 3A
Submode 3A gives an alert when the airplane looses too much inertial altitude after takeoff. The amount of altitude loss depends on the climb rate and radio altitude of the airplane.
This is the alert:
*
Ground proximity light

*
Aural message DON’T SINK.

Submode 3B
Submode 3B gives an alert if the radio altitude terrain clearance goes below the amount stored in a filter in the GPWC, when the gear is up and the flaps are up (less than 15 units).
This is the alert:
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