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2 Automatic Recovery Systems
2.1 Overview
Auto Recovery Systems (ARS) are available, with different levels of sophistication, on various military aircrafts. Examples include some versions of the F-16 and the Eurofigther “Typhoon”, which are provided with a pilot-activated recovery system. Also known as Automatic Disorientation Recovery (ADR) system, it’s a feature of the FCS that attempts recovery to levelled flight.
The ARS:
may either require or not require activation from the pilot, i.e. can be auto-activated intentionally
takes control of the aircraft, with full authority, unless pilot disengages it stays active even after recovery, until pilot is ready to resume control
While on levelled flight, the pilot should have enough time to regain consciousness of its surrounding; after regaining orientation he resumes mission normally.
The ARS control laws depend on the attitude and on the flight conditions at activation. For example, it could be easier to divide the attitude configuration into smaller intervals, and adopt different control laws in each interval. This way, the ARS can be optimized for every starting condition.
Usually the recovery logic behind an ARS takes into account several important factors, and one of them is the pilot’s comfort. If the recovery manoeuvre is done very rapidly, with very high load factors and angular rates, the already-degraded pilot orientation may be further aggravated. However, using slow rates and low load factors implies that recovery will take more time to be obtained, which can have a negative impact for safety.
Hence, is clear that for a satisfactory implementation of an ARS, comfort and safety should be adequately balanced and various solutions should be intensively tested.
Note that ARSs can have some issues which may limit their efficiency, in particular flight conditions. For instance, while an ARS is designed to avoid excessive altitude loss, it still may have no ground avoidance capabilities. Also, if the initial speed is either very low or very high, recovery
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manoeuvres may not be able to guarantee safety. Therefore, an ARS usually is very efficient when far from the envelope limits, and may have safety problems at the limits of the envelope.
A particular kind of ARS known as Ground Collision Avoidance System (GCAS) is an improvement over the Ground Proximity Warning System (GPWS). While the GPWS only alerts the pilot of danger of a crash, the GCAS directly prevents the aircraft from flying into solid terrain. The GCAS takes full control of the aircraft if collision is impending without the need of activation from the pilot, but leaves autonomous flight to him for as long as safety allows.
All in all, an ARS is a useful feature of the FCS and its implementation is worthy of the effort. For more information about ARS and GCAS see [1], [17] and [22].
