737 Flight Crew Operations Manual
Flight Management, Navigation -
Controls and Indicators
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11.10.18 D6-27370-866-EGP
3 Inertial Reference System (IRS) Mode Selector
OFF –
• alignment is lost
• all electrical power is removed from the system after a 30 second
shutdown cycle.
ALIGN –
• rotating the selector from OFF to ALIGN initiates the alignment cycle
• rotating the selector from NAV to ALIGN automatically updates
alignment and zeroes ground speed error.
NAV (detented position) –
• system enters the NAV mode after completion of the alignment cycle
and entry of present position
• in NAV mode, all IRS information is available to airplane systems for
normal operations.
ATT – provides only attitude and heading information:
• attitude information is invalid (attitude flag in view) until ALIGN light
is extinguished
• heading information is invalid (heading flags in view) until the actual
magnetic heading is manually entered after the ALIGN light is
extinguished
• position and ground speed information is not available until the IRS is
aligned on the ground
• the selector must be cycled to OFF before reselecting ALIGN or NAV.
4 ON DC Light
Illuminated (amber) –
• the related IRS is operating on DC power from the switched hot battery
bus (AC power not normal)
• if on the ground, the ground–call horn in the nose wheel well sounds,
providing an alert that a battery drain condition exists
• momentary illumination is normal during alignment self–test.
5 DC FAIL Light
Illuminated (amber) –
• DC power for the related IRS is not normal
• if the other lights are extinguished, the IRS is operating normally on AC
power.
September 15, 2016
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