SLOP (Strategic Lateral Offset Procedure)
 

What is the purpose of SLOP and when do you use it ?

In Europe / North Atlantic it is used when in MNPS Airspace. The theory is that modern navigation systems are so accurate all aircraft will be flying down the same very narrow corridor whereas with less accurate nav systems aircraft would be a bit mor spaced out. (If I remember correctly and airways in 10Nm wide to accommodate this?) Nowadays aircraft could theoretically, and often do, fly within a corridor just a number of metre wide.

With SLOP (where I am based) you offset right by 0, 1 or 2 miles. This in theory means a third of the aircraft are on the centreline of the airway, a third of the aircraft are 1Nm right of the centreline, and a third of the aircraft are 2Nm right of the centreline.

The same applies in the opposite direction, so you now have aircraft spread across 4 miles.

This means less chance of a collision, and provides a safety margin.

NATS (Oceanic) did an excellent video that explains it - I'll see if I can find an online copy.

SKYbrary has an article on this here SKYbrary - Strategic Lateral Offset

There's a link at the bottom of the article to the North Atlantic manual hosted by ICAO EUR. It contains the relevant details for obtaining a hard copy of the video produced by NATS.

The title is "Track Wise — Targeting Risk within the Shanwick OCA." The full video is also available on Youtube:
From the NAT manual: "Like [the North Atlantic Operations and Airspace] Manual, [the DVD] is aimed at pilots, dispatchers and others concerned in flight operations in the North Atlantic. It follows the progress of a westbound NAT flight through the Shanwick OCA as well as exampling contingency and emergencies situations. While the operational procedures elements are specific to Shanwick, the majority of the DVD considers issues common to the whole ICAO NAT Region."

Thank you @dwshimoda and @selfin. Informative and helpful video

Are SLOPs only allowed on oceanic airways or any MNPS airways/routes?

Found another informative video on SLOP.

Its also used in Africa. All that you have to do is enter R01.0 into the FMS and it will parallel your intended track 1 nm offset to the right.

Mutt

SuperflyTNT...
 

The video you posted is the one I was looking for. However, the one posted by Selfin is much more up to date and wide ranging - definitely a useful watch.

Thanks to both.

DW.

SLOP (Strategic Lateral Offset Procedure)
 

There are two things about this concept that don't make sense to me.

1. Why do the rule makers allow only three offset values to choose from. 1, 2, or 3 nm. And why exact whole numbers i.e 2.0 nm. Makes sense to me to encourage fractions of miles too if the aircraft is capable e.g. 2.3 nm. By doing that you've just reduced the chances of collision by a factor of ten!

2. Why not other airspaces around the world where there are two-way air routes such as continental Australia? TCAS has been activated there more than once in recent years.