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Honeywell
MK XXII EGPWS Installation Manual
CAGE CODE: 97896 SCALE: NONE SIZE: A DWG NO: 060-4314-225 REV: C
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3.3.13.12 Timed Audio Inhibit Discrete
The Timed Audio Inhibit will cause the inhibiting of all audio messages for a period of 5 minutes
or until reset. The discrete input is connected to a momentary lighted switch. When pressed the
condition is latched in memory and will be reset after 5 minutes have elapsed or pressing the
switch again or when landing. The switch lighting, indicating the Audio is Inhibited is driven by a
discrete output described below.
Discrete Position / Status Connector Pin
Timed Audio Inhibit Momentary Toggle = Gnd
Normal = Open
J1-17
NOTE: Either the Timed Audio Inhibit or the Terrain Inhibit should be used depending on the
aircraft operations. See discussion is section 1.
3.3.13.13 Low Altitude Mode Select Discrete
The Low Altitude Mode select is a required input and is used for cruise operation below 500 feet
AGL and for operation in high density metropolitan environments such as tall buildings. When
selected, the Low Altitude Mode inhibits Excessive Terrain Closure (Mode 2) warnings, retards
the Terrain Clearance warnings (Mode 4), and reduces the Terrain look ahead distances and
width. When selected, Low Altitude Mode may be de-selected by pressing the switch again.
The Low Altitude select switch is a lighted momentary switch where the selected condition lighting
is driven by an output discrete described below.
3.3.13.14 Output Discretes
The discrete outputs are defined in
Appendix E Section 7.4
. The MK XXII EGPWS supports two
kinds of Ground/Open discrete outputs used to indicate various conditions. Monitor outputs are
used to indicate failure conditions for the EGPW system. Monitor outputs default to an active
state when there is a failure or if power is removed from the EGPWS (no connection if the
EGPWC is removed from the rack). The Discrete Out Lamp driver outputs are used to indicate
alert modes (GPWS WARN, BELOW GS, etc.) or mode control status (Terrain Display Select,
etc.) of the EGPWS.
Short-term current limit protection is provided on all drivers for output shorting conditions. Ground
going output discretes may be connected together to produce a ‘wired OR’ function for the active
low state of the outputs. If output discretes are ‘wire OR’d’ then diodes must be installed for
isolation.
3.3.13.15 Lamp Format
The Lamp Format Type (configuration) is a function of the discrete output pin functions and
defines the operation of the red and amber GPWS cockpit lamps.