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Tuesday, February 20, 2007

Airways Offsets

Flight Safety Foundation (FSF) president Bill Voss is joining the throng of airline pilot voices calling for track offsets on airways that could avoid head-on collisions. Recent findings by analysis of the Embraer Legacy and GOL 737 CVR tapes indicate that neither flight-crew had any sense of alarm or impending danger as their head-on collision was imminent. Neither aircraft would have had their landing lights lit up either. That is a measure that is used by some pilots and not by others. In a similar fashion, some airlines allow their crews to use the embedded offset capabilities within Flight Management computers to achieve a half-mile offset, and some will not. As reported in the Air Safety Week dated 19 Feb 2007 (The Chronic Deficiencies of Collision Avoidance), the use of offset tracking, known as SLOP, or Strategic Lateral Offset Procedure, has been in use on the North Atlantic Tracks for years, but only as a wake avoidance measure for same direction traffic. It's fallen into dis-use because it is inflexible in its application, requiring crews in close proximity to communicate with each other (after first establishing each other's identities). Airways Offset Tracking, by comparison, is a vital need to avoid the one error that can kill two jumbo-fuls.

Speaking at the ATC Maastricht 2007 conference on 14 Feb, Voss said the fatal head-on collision in Brazil last year proved that the track offset issue needs revisiting. He maintains that much has changed since the original rules mandating centerline flying were written in the late 1970s. Accurate centerline flying and resistance to offsets stem from an en-route environment dominated by VOR-designated airways and comparatively inaccurate onboard VOR tracking. Modern flight management system-flown area navigation using DME/DME (multiple distance measuring system fixes) and satellite navigation has made centerline maintenance deadly accurate but also enabled manageable offset flying.

No review of the risks of precision centerline flying on two-way airways has taken place, Voss says, and calls from pilot organizations for organized offset flying have been ignored. FSF considers reviewing approved practices and listening to operator's concerns is a badly needed safety omission.
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