Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 56
6.2.2.2 Mode 2A Altitude Gain
When the Mode 2A envelope is exited, after having been violated for more than 3 seconds, an altitude gain feature is
automatically activated. Altitude (MSL) is sampled at this time to compute subsequent changes in altitude. The caution lights
(warning lights if using Lamp Format 1) remain on, and if the terrain is still closing the voice message is “Terrain”.
After three hundred feet of Altitude (MSL) has been gained, or 45 seconds have elapsed from the point where the Pull-Up
envelope was exited, all caution/warning lights and voices stop. The altitude gain requirement can also be canceled by
momentarily selecting the flap override switch. If the terrain starts to fall away during this altitude gain time, the voice will
shut off. In addition if the radio altimeter goes out of track (data NCD) then both the caution/warning lamp and voice are
disabled.
If another envelope penetration occurs during this altitude gain time, and it lasts long enough to restart the “Pull Up” warning
plus 3 seconds, then the whole process begins again with a new reference point for the 300 foot gain feature. In this manner
the aircraft is directed up and over the terrain to a safer altitude.
6.2.2.3 Mode 2B
Lowering the flaps to the landing position automatically switches the system to Mode 2B as illustrated in 6.2.2.3-1. This static
envelope is the same as the Mode 2A envelope, except the upper altitude boundary has been lowered to 789 feet, due to a
maximum allowed closure rate of 3000 FPM.
The Mode 2B envelope is also selected with flaps up, when the aircraft is performing an ILS approach and glideslope is less
than ±2 dots. However, the alert envelope is slightly different than 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 feet AGL. Whenever the flaps are selected
to the landing position the lower boundary of Mode 2B is desensitized in the region controlled by Figure 6.2.2.3-2.
The Mode 2B envelope is also selected automatically during the first 60 seconds after takeoff. This is to eliminate the false
“Terrain” alerts that have occurred during certain cases of erroneous radio altitude tracking after takeoff. What occurs is
typically a sharp increase, followed by a sharp decrease in the altitude output between 1000 and 1500 feet AGL. This Mode 2
‘Takeoff’ mode effectively prevents Mode 2 alerts for altitudes above 789 feet AGL. This limit is also enabled when the
TA&D functions are operating with high integrity (valid with good position and terrain data) and the aircraft is near an
airport.
When the envelope for Mode 2B is penetrated, the caution/warning lamps come on, and the voice message is repeated until
the envelope is exited. If the landing gear or flaps are up, then the voice message will be “Terrain-Terrain” or equivalent,
followed by “Pull Up” if the condition persists. If both landing gear and flaps are in the landing configuration, then the
message will be “Terrain”.