Automatic Flight -
Autoland Status Annunciators (ASA)
Autoland Status Annunciators (ASA) provide information relative to the status of the autopilot systems for CAT II and III approaches with automatic landing and rollout. An ASA is located on each Pilot's Panel to display this information. Each ASA has an upper and lower display, which shows one of three indications. Except during test, both ASAs show the same Indication.
Monitoring of the autopilot systems is initiated by the Autoland status system when the electrical system is powered. A fault which limits the autopilot system, is shown as NO LAND 3 or NO AUTOLND on the ASAs. Should the limiting fault(s) clear prior to the selection of APP mode, the ASA will blank when APP mode is selected. Faults that do not require immediate crew action or cognisance are annunciated after touchdown.
The following AFDS status annunciations can be displayed:
- LAND 3 - Three autopilots engaged and operating normally for an automatic landing.
- LAND 2 - AFDS redundancy reduced, in some cases only two autopilots available.
- NO LAND 3 - Indicates a fault condition exists which results in a LAND 2 condition.
- NO AUTOLND - AFDS unable to make an automatic landing.
With a LAND 3 indication, the autopilot system level of redundancy is such that a single fault cannot prevent the autopilot system from making an automatic landing (fail operational).
With a LAND 2 indication, the level of redundancy is such that a single fault cannot cause a significant deviation from the flight path (fail passive).
During Autoland operations, the FCC detects ILS system anomalies. LAND 3 and LAND 2 annunciations do not necessarily mean that the Localiser and Glideslope signals are being received. If the ILS station fails or goes off the air, the airplane continues on an inertial track. After a short delay, an amber line is drawn through the affected EADI mode annunciation (G/S or LOC) and the affected flight director commands are removed from view. Also, the AUTOPILOT and master CAUTION lights illuminates and the caution beeper sounds. The ASA annunciation may or may not change.
An EICAS message displays for any fault limiting the capability of the automatic landing system. Below 200 feet Radio Altitude the ASA display cannot change except to indicate a NO AUTOLND condition. Faults not requiring immediate crew action or awareness are annunciated after touchdown.
The ASA system does not monitor the status of all ground and airborne equipment required for CAT II and III operations. It is primarily an autopilot support system monitor.
