Technical data

Product Specification
HIF-2121/R5 CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 965-1176-601 REV: D SHEET 64
4A) or with landing gear down and flaps not in landing position (and not overridden) “Too Low Flaps”. For aircraft types
that routinely delay full flap deployment (Mode 4 Types 8 and 9) these airspeeds are 148 knots and 118 knots respectively.
To maintain the same airspeed expansion function up to 750 feet nominal at 200 knots the lower level “corner” is at 150 knots
(Mode 4 Type 6), or 120 knots (Mode 4 Type 7) while above this airspeed the message is “Too Low Terrain”. For aircraft
types that routinely delay full flap deployment (Mode 4 Types 8 and 9) these airspeeds are 148 knots and 118 knots
respectively.
Mode 4B is slightly modified for turboprop aircraft (Mode 4 Type 1). Penetration of the Mode 4B envelope below 159 knots
with gear up results in “Too Low Gear” or with landing gear down and flaps not in landing position (and not overridden)
“Too Low Flaps”. To maintain the same airspeed expansion function up to 1000 feet at 250 knots the lower level “corner” is
at 159 knots while above this airspeed the message is “Too Low Terrain”.
The “Too Low Gear” voice will be substituted with “Too Low Flaps” and the condition will be based on flaps up in lieu of
gear up.
The Mode 4B envelope can also be selected by setting flaps to landing configuration or by selecting flap override. This
provides the means to allow additional maneuvering room for marginal performance go-arounds (e.g. engine out).
The airspeed expansions for Mode 4A and 4B are disabled when Terrain Awareness data is of high integrity.
The equation for the sloped portion of the alert curves for Mode 4A is:
MIN TERRAIN CLEARANCE (FT) = -1523 + 11.36 [CAS (KNOTS)] – normal airspeed range
MIN TERRAIN CLEARANCE (FT) = -1182+ 11.36 [CAS (KNOTS)] – alternate airspeed range
The equation for the sloped portion of the alert curves for Mode 4B is:
MIN TERRAIN CLEARANCE (FT) = -1570 + 11.6 [CAS (KNOTS)] – normal airspeed range
MIN TERRAIN CLEARANCE (FT) = -1222+ 11.6 [CAS (KNOTS)] – alternate airspeed range
The equation for the sloped portion of the alert/warning curves on turbofan aircraft for both Mode 4A and 4B is:
MIN TERRAIN CLEARANCE (FT) = -1083 + 8.333 [CAS (KNOTS)]
A ratchet function is applied to the Mode 4 voice that is similar to the Mode 3 ratcheting voice message. Once the message is
given, the envelope is biased down by 20% and further alerts are held off until this additional 20% radio altitude is lost. The
caution/warning lamps are not affected and will remain on until the radio altitude becomes greater than the curves of Figures
6.2.4.1-2 through 6.2.4.1-8.
AIRSPEED (KTS)
M
IN
T
E
R
R
A
IN
C
LE
A
R
A
N
C
E
(F
T
)
0
ALERT AREA
EXPANDED
ALERT
AREA
30 FT
200 KTS
1000 FT
200 FT
0 100 200 300
Normal
148 KTS
1000
800
600
200
400
800 FT LIMIT DURING OVERFLIGHT
FIGURE 6.2.4.1-4: MODE 4B STATIC ALERT ENVELOPE (NORMAL AIRSPEED EXPANSION, MODE TYPE 5)