Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 62
knots (for Mode 4 Types 7,9) the upper boundary increases linearly with airspeed to a maximum of 750 feet radio altitude at
200 knots or more (170 knots for alternate airspeed range). One exception to this is for Mode 4 Type 5 where it increases to
200 knots at 1000 feet. Penetrating this boundary produces a repetitive “Too Low Terrain” message.
When TAD is operating with a high level of confidence the speed expasion is inhibited thus inhibiting the Mode 4 “Too Low
Terrain” warnings above the “Too Low Gear” or “Too Low Flaps” floor. This applies to all aircraft types. A high level of
confidence is when TA&D and TCF are functioning over a geographical area with high quality terrain data or large bodiew of
water, and there is a high degree of estimated accuracy in horizontal position and vertical positon.
AIRSPEED (KTS)
100 200 300 400
M
IN
T
E
R
R
A
IN
C
L
E
A
R
A
N
C
E
(F
T
)
1200
1000
800
600
400
200
0
500 FT
750 FT
178 KTS
200 KTS
30 FT
ALERT AREA
TOO LOW GEAR
EXPANDED ALERT AREA
TOO LOW TERRAIN
FIGURE 6.2.4.1-2: MODE 4A STATIC ALERT ENVELOPE (NORMAL AIRSPEED EXPANSION, MODE 4 TYPES 6,8)
Through Envelope Modulation other maximums are used at certain airports to minimize nuisance warnings.
AIRSPEED (KTS)
100 200 300 400
M
IN
T
E
R
R
A
IN
C
L
E
A
R
A
N
C
E
(F
T
)
1200
1000
800
600
400
200
0
500 FT
1000 FT
178 KTS
200 KTS
30 FT
ALERT AREA
TOO LOW GEAR
EXPANDED ALERT AREA
TOO LOW TERRAIN
800 FT LIMIT DURING OVERFLIGHT
FIGURE 6.2.4.1-2A: MODE 4A STATIC ALERT ENVELOPE (NORMAL AIRSPEED EXPANSION, MODE 4 TYPE 5)
The standard upper boundary for Mode 4A (turbofan aircraft) is at 500 feet radio altitude. If the aircraft penetrates this
boundary with the gear still up, the voice message will be “Too Low Gear”. Above 190 knots the upper boundary increases
linearly with airspeed to a maximum of 1000 feet radio altitude at 250 knots or more. Penetrating this boundary produces a
repetitive “Too Low Terrain” message. See Figure 6.2.4.1-2B for a pictorial representation of the alerts.