Fail-passive Automatic Landing System
An automatic landing system is fail-passive if, in the event of a failure, there is no significant out-of-trim condition or deviation of flight path or attitude but the landing is not completed automatically.
NOTE: For a fail-passive automatic landing system the pilot assumes control of the aircraft after a failure.
The following are typical arrangements:
(1) A monitored automatic pilot in which automatic monitors will provide the necessary failure detection and protection.
(2) Two automatic pilots with automatic comparison to provide the necessary failure detection and protection.
Fail-operational Automatic Landing System.
An automatic landing system is fail-operational if, in the event of a failure, the approach, flare and landing can be completed by the remaining part of the automatic system.
NOTE: In the event of a failure, the automatic landing system will operate as a fail-passive system.
The following are typical arrangements:
(1) Two monitored automatic pilots, one remaining operative after a failure.
(2) Three automatic pilots, two remaining operative (to permit comparison and provide necessary failure detection and protection) after a failure.
Fail-operational Hybrid Landing System
A system which consists of a primary fail-passive automatic landing system and a secondary independent guidance system enabling the pilot to complete a landing manually after failure of the primary system.
NOTE: A typical secondary independent guidance system consists of a monitored head-up display providing guidance which normally takes the form of command information, but it may alternatively be situation (or deviation) information.
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