737 Flight Crew Operations Manual
Flight Instruments, Displays -
Head-Up Display System –
Controls
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D6-27370-866-EGP 10.17.5
5 AIII Approach Mode
The HGS AIII mode is specifically designed for manual ILS approach and landing
operations to CAT IIIa minimums. In the AIII mode, the guidance cue gives flight
path guidance derived from HGS internal approach and landing guidance
algorithms.
Note: CAT IIIa operations are not standard operating procedures. Consult
applicable directives and obtain approval from command operational
authorities before initiating or conducting CAT IIIa HGS low visibility
approaches to landing.
The AIII mode can be set manually or automatically, but it starts operating only
after ILS capture. In manual selection, "AIII" flashes in the upper left of the
Combiner display, at which time the pilot can select the AIII mode on the MCDU
any time while the aircraft is above 500 feet AGL. In automatic selection, the pilot
needs to arm AIII mode on the MCDU. The message "AIII ARM" shows on the
upper left of the Combiner display, and "AIII" flashes for 5 seconds before the
HGS automatically changes to AIII mode.
In AIII mode, the HGS removes the altitude and airspeed tape displays and
replaces them with numeric representations. The HGS also replaces the HSI,
displaying instead ILS raw data in proximity to the flight path group near the
center of the display.
When available, AIII capability status is displayed adjacent to the standby mode.
“A
III” changes to “AIII” and moves to the standby mode once all conditions have
been met to conduct an AIII mode approach. Pressing the mode key then activates
the AIII mode.
Automatic AIII arming is indicated by “AIII ARM” displayed as the standby
mode. Once all requirements are satisfied for an AIII mode approach, AIII mode
is automatically activated. Refer to Section 10-22, Head–Up Display System
Description, for AIII mode arming requirements.
Even if the HGS is capable of providing AIII guidance, AIII mode cannot be
activated until the following Approach On Course (AOC) conditions are satisfied:
• Both VHF Navigation Receivers are tuned to an ILS frequency
• The difference between the aircraft’s magnetic track and the pilot’s
selected course is less than 15 degrees
• Radio altitude is greater than 500 feet
• VHF Nav #1 or VHF Nav #2 localizer deviation is less than
approximately ¼ dot and glideslope deviation is less than approximately
1 ¼ dots for at least five seconds.
March 27, 2014
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