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R R R R R R  (h) When the envelope boundary conditions for Mode 2B are violated, the PULL UP 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 is TERRAIN TERRAIN followed by PULL UP if the condition persists. If both gear and flaps are in the landing configuration, the message is TERRAIN. 
R R  (i) When Geometric Altitude is activated and the following conditions are available: 
R R R R R R R R  - Enhanced functions valid, - Terrain database quality good, - Geometric Altitude valid, - Terrain awareness functions in high integrity, Current Mode 2 alert envelopes are modified in order to limit spurious alert. The new envelope limits the top of the Mode 2 curve to 1250 ft. RA. 
R R  The Mode 2 envelope is also reduced to the existing Mode 2 B limit of 789 ft.whenever the aircraft is within 5NM of the 
R R  runway. (Ref. Fig. 012)
 **ON A/C ALL
 (3) Mode 3 - Insufficient climb performance after takeoff (Ref. Fig. 013)
 (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).
 (b) Penetration of the Mode 3 alert/boundary results in the message DON'T SINK and is based on altitude loss and radio altitude. This
 alert/warning is only provided during takeoff when the aircraft looses a predetermined amount of altitude. (Ref. Fig. 013) The sloped portion of the static warning envelope depicted is defined by the following equation:
 ALTITUDE LOSS (FT.) = 5.4 + 0.092 (RADIO ALTITUDE (FT.)) 

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 Enhanced GPWS - Mode 2 with Geometric altitude
 Figure 012

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 Enhanced GPWS - Descent After Takeoff R Figure 013
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 (c)
 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.

 (d)
 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 Enhanced GPWC stores 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.

 (e)
 Mode 3 is biased or desensitized under certain conditions. This is accomplished by sampling radio altitude and altitude at takeoff or go-around, and combining these signals to establish the field elevation (or ground elevation) at takeoff or at the point of go-around. Subsequent altitude information is then compared to this value to determine the altitude gained since takeoff or go-around.

 (f)
 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.

R
 (4) Mode 4 - Unsafe terrain clearance
 (a) Mode 4 generates three types of voice warnings based on the radio altitude, computed airspeed, and aircraft configuration, commonly referred to as Modes 4A, 4B and 4C. Mode 4A is active during cruise and approach with gear and flaps not in landing configuration. Mode 4B is active in cruise and approach, with either gear or flaps in landing configuration. The upper boundary of the mode 4A and 4B envelope depends on the enhanced mo des. When TCF is enabled and TAD in high integrity,
 1EFF : ALL 1 34-48-00Page 91 1 1 Config-1 Aug 01/05 1 1 1CES 1 mode 4A upper boundary is maintained at 500ft for all airspeed and mode 4B upper boundary is maintained at 245ft for all airspeed. All mode 4A/4B alerts are disabled when the aircraft is in full landing configuration.
　
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