SLOP

SLOP is a procedure that permits aircraft operating on oceanic and remote routes to fly a lateral offset from the centreline of an ATC-assigned route. On high-traffic oceanic tracks - such as the North Atlantic Tracks (NAT) system - aircraft are separated laterally by a minimum of 60 nautical miles between tracks. However, within a single track, vertical and longitudinal separation standards apply, and a risk exists from wake turbulence and the accumulated navigation errors of multiple aircraft all tracking the exact same centreline. SLOP addresses this by allowing pilots to offset 1 or 2 nautical miles to the right of the centreline without specific ATC clearance. The procedure is mandatory in some regions and voluntary in others, but the standardised options (right only, by 1 or 2 NM) prevent random divergence that would defeat the purpose. SLOP reduces the probability of mid-air collision in the event of a navigation error and also minimises wake turbulence encounters from aircraft ahead at the same altitude. Pilots must notify ATC of the offset being used when making position reports, and the offset must be abandoned if ATC issues a specific track instruction. SLOP is authorised under ICAO procedures and is widely used on North Atlantic, Pacific, and Indian Ocean routes.

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In Virtual Airline Operations

For virtual pilots flying oceanic routes on VACA - particularly transatlantic or transpacific crossings - SLOP is a realistic procedure to apply when using an online network such as VATSIM or IVAO. Some ATC positions on those networks will expect pilots to be familiar with SLOP and to report their offset during oceanic position reports. Applying SLOP correctly is a sign of procedural awareness and contributes to realistic oceanic operations.

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Related Terms

• ETOPS - Extended-range Twin-engine Operations Performance Standards
• HF - High Frequency
• SELCAL - Selective Calling System