Mode 2B - Excessive Closure Rate to Terrain During Landing
The warning envelope for this mode is much smaller, in order to allow flight paths closer to terrain
without nuisance warnings. During an approach to a landing, this mode is armed when the flaps are
in the landing configuration or the flap override mode has been selected, and the airplane is on a
glide slope not more than 1.3 dots below the glide slope and the G/S CANCEL function has not been
selected. Terrain closure rates between 2,500 and 10,000 feet per minute at less than 750 feet AGL
will result in a red PULL UP light and the message "TERRAIN - TERRAIN" followed by a continuous
"PULL UP" warning. If this mode is entered with the landing gear extended and the flaps in landing
position, the red PULL UP light will illuminate and the message "TERRAIN - TERRAIN" will be heard.
There will be no PULL UP warning.
Mode 3 - Descent after Takeoff
After takeoff or go around from an altitude below 245 feet AGL, a negative rate-of- climb for a specific
altitude loss will trigger an aural warning of "DON'T SINK". The mode becomes active when the
airplane leaves the ground or begins a go-around and the EGPWS senses the airspeed increasing,
no weight on wheels, the radio altitude increasing, and the landing gear and flaps retracted. Above
an altitude of 50 feet AGL the EGPWS monitors both radio and barometric altitudes.
If the airplane begins to descend toward terrain, a comparison of radio altitude gained to that point is
made with the barometric altitude being lost in the descent. When the barometric altitude loss
becomes approximately 10% of the radio altitude gained, the red PULL UP light will illuminate and
the alert message "DON’T SINK" will be announced every three seconds. Once a positive rate of
climb is re-established, the alert message will cease and the red PULL UP light will extinguish. In
order to reduce nuisance warnings above 700 feet AGL, the alert envelope is shifted by five feet per
second to allow greater loss of altitude before the alert is activated.
Mode 4A - Proximity to Terrain with the Landing Gear Retracted
This mode is intended to give protection against flying into terrain in cruise configuration. If an
airplane has slowly descended toward relatively flat terrain or the terrain has risen slowly under the
airplane, there will be no excessive descent rate warning as in Modes 1 or 2. This mode will also
guard against making a gear up landing.
With the landing gear and flaps in the retracted position, the EGPWS monitors the radio altitude and
airspeed. At speeds greater than 178 knots indicated airspeed (IAS), the EGPWS will illuminate the
red PULL UP light and provide the aural warning "TOO LOW, TERRAIN" every three seconds
between 750 and 500 feet AGL. The purpose of this warning is to alert the pilot of proximity to terrain
at high airspeed. By climbing above the altitude at which the alert began, a safe terrain clearance will
be re-established and the warnings will be canceled.
At airspeeds less than 178 knots IAS, the EGPWS monitors the aircraft configuration, since at lower
airspeeds the crew is more likely to be preparing the airplane for landing. If the gear are not extended
before the airplane is less than 500 feet altitude AGL, the warning "TOO LOW GEAR" will be
repeated every three seconds and the red PULL UP light will illuminate. Extending the landing gear
or climbing above 500 feet AGL will silence the warning. No warning will be heard if the landing gear
is extended before the airplane descends through 500 feet altitude AGL.
Cessna Citation XLS - Instrumentation & Avionics
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