"Strategic Lateral Offset Procedures (SLOP) are approved procedures that allow aircraft to fly on a parallel track to the right of the centre line relative to the direction of flight to mitigate the lateral overlap probability due to increased navigation accuracy and wake turbulence encounters."

ICAO 4444 Pans ATM 16th Edition section 16.5 Note 1.

SLOP of one or two nautical miles has been recommended for use in oceanic and remote continental airspace for a long time. For example, the North Atlantic Track (NAT) system has permitted SLOP since 2004 and has been a mandatory requirement to fly SLOP over the North Atlantic since 2017.

In the 16th Edition of ICAO 4444, published in 2015, ICAO extended the use of SLOP to en-route airspace in tenths of a nautical mile up to a maximum of 0.5NM, i.e. Micro-SLOP.

This change was originally proposed in ICAO Circular 331 to counter the effect of the navigation paradox after the mid air collision over Brazil in 2006, see Gol Transportes Aéreos Flight 1907.

Currently, Micro-SLOP may only be applied on routes promulgated in AIPs by aircraft equipped with the appropriate automatic offset tracking capability.

Most ANSPs do not permit Micro-SLOP in their AIPs. However, the NAT recommendations have recently changed to recommend that pilots fly Micro-SLOP over the North Atlantic, see Two is not enough.

My pilot friends tell me that small commercial aircraft fitted with the Universal Avionics SCN 1000 and 1100 FMS's can fly 0.1NM offsets but that Airbus A320's can only fly offsets in 1NM increments.

The question is: which commercial aircraft currently have the capability to fly Micro-SLOP procedures with route offsets of only 0.1NM?

  • 1
    $\begingroup$ Welcome to Av.SE! Interesting question. $\endgroup$
    – Ralph J
    Aug 23, 2019 at 8:01

1 Answer 1


According to the below references, these commercial aircraft are capable of doing the Micro-SLOP procedures with 0.1 NM increments:


2.6.2 Most flight management systems in service today can execute an automatic offset track in whole nautical miles. Unfortunately, as offsetting by tenths of a nautical mile was only introduced in ICAO provisions in 2014, most flight management systems are currently incapable of executing such offsets. Of the major aircraft and flight management system combinations in production, only the Boeing BBJ, 737 and 787 are currently capable of offsetting in tenths of a nautical mile. Depending on the aircraft mix in the airspace, even if a State permits offsetting in tenths of a nautical mile, the majority of aircraft may not be able to participate in this SLOP, and the full benefits may not be realised.

  1. Cir 331 A /192N Implementation of Strategic Lateral Offset Procedures ICAO

1.3.8 The idea quickly emerged to employ the capability of some modern aircraft to offset in fractions of a mile for this purpose. Both Boeing and Airbus announced that all their future aircraft would have the capability to offset in tenths of a mile and it was therefore clear that using such “micro-offsets” to mitigate the collision risk would be viable in the future.

  1. IFALPA (International Federation of Air Line Pilots’ Associations) Saftey Bulletin (NAT Lateral ASEPS)

Micro-SLOP is currently authorized throughout the NAT region. The latest information available to ALPA is that the most recent Boeing B737s (NG, Max), B787s, and the B777X (when it enters service) have Micro-SLOP capability. Airbus is planning an enhancement across their product offerings in the 2022+ timeframe. There is no hazard introduced by this mixed implementation of Micro-SLOP.

  • $\begingroup$ I know I'm not supposed to say thank you... but thank you. That's precisely the kind of answer I was looking for! I wonder why Airbus is so far behind Boeing on this? $\endgroup$
    – kenba
    Dec 13, 2019 at 15:06

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