(b)
The aural warning changes to PULL UP if the airplane sink rate continuous and penetrated the warning area as shown in Fig. 4. The PULL UP warning boundary is below the SINK RATE warning boundary.
H31435
504 Mode 1 Pull-Up Envelope
Nov 15/79 Figure 4 34-42-01
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(2) Closure Warning (Mode 2)
(a) With the flaps not in landing configuration, (airplane in cruise) the computer will provide the pilots with a warning if the airplane exceeds the terrain closure rates with respect to the terrain clearances shown in Fig. 5. The PULL UP indicator and two cycles of aural warning TERRAIN come on. If the airplane remains within the curve boundary, the aural warning will change to PULL UP, repeated every 0.75 seconds. Upon leaving the curve boundary, due to either terrain change or pull up maneuver, the aural warning will change to TERRAIN, repeated every 0.75 seconds. The warning will remain on until the barometric altitude has increased by 300 feet. During high speed operation, the upper curve boundary is increased linearly between 0.35 and 0.45 mach to provide early warning.
H31438
Mode 2A Warning Envelope Flaps Up 508
34-42-01 Figure 5 Sep 20/82
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(b)
With flaps in the landing configuration, the warning boundary is limited as shown in Fig 6. No altitude gain is required to turn off the TERRAIN aural warning after the PULL UP aural warning is activated. The PULL UP aural warning is inhibited at radio altitude below 700 feet with landing gears down. Only the TERRAIN aural warning is activated.
(c)
To provide additional nuisance warning protection at the runway threshold during steeper approaches, the lower limit of mode 2B varies as a function of barometric rate as shown in Fig. 7.
H31485
533 Mode 2B Lower Cutoff
May 20/82 Figure 7 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 34-42-01 Page 9
(3) Takeoff Altitude Loss Warning (Mode 3)
(a)
A warning consists of visual PULL UP and aural DON’T SINK is provided when the airplane is in takeoff mode before acquiring 700-foot terrain clearance with landing gear or flaps up and a barometric altitude loss is detected as shown n Fig. 8. The altitude loss required to activate the warning varies with the height of the airplane above the ground at the time of inadvertent descent occurs. At a climbout altitude of 100 feet, any loss of altitude will activate the warning. At 700 feet, an altitude loss of 70 feet will activate the warning.
(b)
A magnetic latch provides logic between mode 3 and 4. During takeoff, the latch is set to arm the takeoff mode and disarming the terrain clearance warning. Upon acquiring 700 feet of altitude, the latch resets, arming the terrain clearance warning.
H28981
Mode 3 Warning Envelope 533
34-42-01 Figure 8 Feb 15/78
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.
(4) Unsafe Terrain Clearance Warning (Mode 4)
(a)
With landing gear not down, the computer will provide a warning if the airplane is below 500 feet and speed below 0.35 mach, as shown in Fig. 9. The warning consists of the captain's and first officer's PULL UP lights coming on and an aural TOO LOW-GEAR repeated every 0.75 second. On GUN B-2504, B-2505, B-2509, B-2510 and XIA B-2524, setting the FLAP/GEAR INHIBIT switch to the INHIBIT position will cause all warnings to cease. For speed above 0.35 mach, the aural warning changes to TOO LOW-TERRAIN, repeated every 0.75 second and the warning threshold increases linearly to a maximum of 1000 feet above the terrain.
(b)
With landing gear down, the minimum warning threshold decreases to 200 feet and a TOO LOW-FLAPS warning comes on if the flaps are not in landing configuration as shown in Fig. 10. The warning may be inhibited by setting the FLAP (FLAP/GEAR) INHIBIT switch on the ground proximity warning module to INHIBIT position. This will simulate a flaps down condition if the pilot prefers to land with less than normal landing flaps. A magnetic latch is used to select mode 4A or mode 4B, so that power interruption or missed approach below 500 feet prevent reactivation of mode 4A until at least 700 feet of terrain clearance is reached.
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