(e)
Upon penetration of the boundary, either on the slope or from the top, the GPWS legends come on and the voice message is TERRAIN. If the boundary penetration lasts beyond two TERRAIN messages, approximately 1.4 seconds, then the warning switches to WHOOP WHOOP/ PULL UP repeated continuously until the boundary is
R 1EFF : 001-049, 051-060, 101-104, 1 34-48-00Page 26 1 1 Config-2 May 01/05 1 1 1CES 1 departed. The altitude gain feature is automatically activated. First the altitude at this instant is sampled and stored. The GPWS legends remain on and the voice message is TERRAIN. After three hundred feet of altitude are gained from the stored value, the GPWS legends and voice stop. If another boundary penetration occurs during this altitude gain time, and it lasts long enough to restart the PULL UP warning, 1.4 seconds, then the whole process begins again with a new reference altitude for the 300 ft. after boundary separation. In this manner the aircraft is directed up and over the terrain to a safer altitude.
(f)
Lowering the flaps to the landing position automatically switches the GPWS to Mode 2B. The static boundary for Mode 2B is the same as the Mode 2A boundary except the upper limit has been lowered to 789 ft. at a maximum closure rate of 3000 FPM. The lower part of the Mode 2B boundary is controlled as a function of radio altitude and altitude rate when flaps are in full landing configuration.
(g)
Mode 2B is also selected when the aircraft is performing an ILS approach and the glide slope deviation is less than +/- 2 dots. However, the warning envelope is slightly different from the flaps down case in that the lower boundary is controlled only as a function of radio altitude, having a constant lower cutoff of 30 ft. above ground level. When the flaps are selected to landing configuration in the ILS glide slope beam, the lower boundary is activated.
(h)
When the envelope boundary conditions for Mode 2B are violated, the GPWS legends come on, and the voice message is repeated until the boundary is exited. If the gear or the flaps are up, then the message will be TERRAIN TERRAIN followed by WHOOP WHOOP PULL UP if the condition persists. If both gear and flaps are in the landing configuration, the message will be TERRAIN.
(3) Mode 3 - Insufficient climb performance after takeoff (Ref. Fig. 009, 010)
(a) Mode 3 provides a warning for excessive altitude loss after takeoff. Mode 3 is based primarily on radio altitude, altitude (IR inertial altitude, internally computed inertial altitude, or barometric altitude), and altitude rate (IVS, internally computed inertial altitude rate, or barometric altitude rate).
R 1EFF : 001-049, 051-060, 101-104, 1 34-48-00Page 27 1 1 Config-2 May 01/05 1 1 1CES 1
(b)
Inertially compensated air data signals are used when possible. IVS is used when valid data is available and barometric altitude rate is used only when valid IVS is not available and the internal computed inertial data is not valid. The Mode 3 warning envelopes are inhibited close to the ground.
(c)
The descent required for a warning varies as a function of flight profile and time. Once a descent begins during the takeoff phase of flight, as determined by the polarity of the altitude rate signal and takeoff/approach mode logic, the GPWC will store the existing value of altitude. Subsequent samples of altitude, altitude rate, and radio altitude are examined for warning conditions. The original stored value of altitude indicating where the descent began is retained until the aircraft ascends above the stored altitude value. When the polarity of the altitude rate signal indicates ascent rather than descent, the warning is cut off to indicate recovery is being initiated. A subsequent return to descent prior to regaining the altitude lost enables the warning. The altitude loss required to resume the message and legend activation is based on the initially stored altitude value. In this manner, the possibility of stair stepping down without Mode 3 warning indication is eliminated.
(d)
Mode 3 is biased or desensitized under certain conditions. In the Mode 3 operation, as more radio altitude and time are accumulated after departure, the warning envelope is effectively moved to the right, allowing more altitude loss. This is accomplished using an integrated function of radio altitude to control the Mode 3 bias or washout. Greater radio altitude and increasing time will gradually desensitize the warning criteria. For example, at 400 ft. radio altitude, the altitude loss required for a warning increases at the rate of 0.4 feet per second.
(e)
A delay equivalent to 0.8 second is added to the warning output to prevent the possibility of nuisance warnings caused by static pressure disturbances during gear retraction.
(4) Mode 4 - Unsafe terrain clearance (Ref. Fig. 010)
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