Authority urges airlines to review SLOP procedures
Pilots employing lateral offsets on North Atlantic tracks (NAT) have been wrongly using individual interpretations of how the International Civil Aviation Organisation procedure should be flown, says the UK Civil Aviation Authority in a flight operations department communication. The CAA says it has not been made clear that the prescribed offset distances are designed to be followed precisely, not approximately at pilots' discretion.
Strategic lateral offset procedures (SLOP) are used to reduce conflict risks introduced by the sheer accuracy of modern navigation aids, which tend to put on-track aircraft precisely above or below each other, increasing the risk of collision if either aircraft diverges from its cleared height. The CAA has recommended that airlines review their operations manuals to ensure SLOP instructions are clear, and that the procedures should be "incorporated in all initial, conversion and recurrent training".
Only three choices are laid down by ICAO for correct SLOPs, says the CAA: on-track; 1nm (1.85km) right of track; or 2nm right of track. In choosing which to employ, pilots can use visual means, traffic alert and collision avoidance system information or communication with the other aircraft, but they must stick to the exact prescribed offset distances and never go left of track nor further right than the 2nm maximum. If a flight management system cannot be programmed for automatic offset, the pilot must fly the centreline, says the rule.
DAVID LEARMOUNT / LONDON
Source: Flight International
