060-4314-000 • Rev. C - May 2004
MK VI & MK VIII EGPWS Pilot Guide
17
Unsafe terrain clearance gear up turboprop
MODE 4A
Mode 4A is active during cruise and approach with gear up. This
provides alerting during cruise for inadvertent flight into ter
-
rain where terrain is not rising significantly, or the aircraft is not
descending excessively. It also provides alerting for protection
against an unintentional gear-up landing.
The standard boundary for Mode 4A is at 500 feet AGL. Penetra
-
tion of this altitude below an airspeed of 178 knots will produce
an aural alert of “TOO LOW GEAR“. The airspeed limit is 148
knots if the alternate airspeed configuration has been selected,
and it is 190 knots for turbofan (bizjet) aircraft.
Above 178 knots, the boundary increases linearly with airspeed
to a maximum of 750 feet AGL at 200 knots to produce a “TOO
LOW TERRAIN” aural alert. If the alternate airspeed configura-
tion has been selected, the slope begins at 148 knots and ends at
170 knots and 1000 feet AGL. For turbofan (bizjet) aircraft, the
slope begins at 190 knots and ends at 250 knots and 1000 feet
AGL. (See following graphs)
For any Mode 4A alert, subsequent aural messages occur only if
penetration of the envelope increases by 20%. EGPWS alert lights
extinguish and aural messages cease when the Mode 4A alert
envelope is exited.
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