T he International Federation of Air Line Pilots Associations (IFALPA) has sharply criticised the UK Civil Aviation Authority for issuing guidelines which IFALPA claims effectively "-advise or encourage" pilots to disregard traffic-alert and collision-avoidance-system II(TCAS II)resolution advisories (RAs).
The CAA guide lines, issued on 25 February, cover operation of the TCAS II in reduced vertical-separation minima (RVSM) airspace over the north Atlantic. The RVSM should become available from 27 March. Reduced vertical separations are expected to lead to more TCAS II advisories, as aircraft routinely climb and descend.
The CAA Aeronautical Information Circular (AIC) states: "RAs may be disregarded only when pilots visually identify the potentially conflicting traffic and decide that no deviation from the current [altitude] is needed."
IFALPA has reacted by issuing its members with a warning that "-pilots should never be advised or encouraged to disregard RAs. Compliance with RAs should be the rule, except when to follow the RA would take the aircraft into direct collision with another aircraft, the ground, or into some other catastrophic flight hazard."
IFALPA also argues that pilots will not have enough time to decide whether or not to comply with an RA, given the very high closing speeds which can be involved.
The current version of the TCASII uses different "logic" when the aircraft is flying below 29,000ft (8,900m), because most traffic is climbing or descending at these altitudes. Above this height, however, the system assumes that most traffic is in level flight. The introduction of RVSM between 33,000ft and 37,000ft will lead to aircraft flight crews carrying out "step climbs" more often, potentially triggering TCAS II RAs.
Source: Flight International
