SLOP in NAT HLA

[extricate]

Hi there,

I just want to get a clarification on this. I was reading Skybrary on SLOP and it mentions:

"f obstacle clearance considerations or other reasons apply, ANSPs are required to restrict the use of strategic lateral offsets. Lateral offset cannot be operated if parallel route centrelines are less than 30 nm apart."

As we know, NAT system has 1/2 degree NAT, which essentially is 25nm apart. If so, can SLOP still be practised in NAT HLA?

Thanks

[rudestuff]

Maybe read up on how a nautical mile is defined...

[extricate]

This brings me to another ques. understand 1deg = 60nm, But I have seen articles and notices of RlatSM being 23nm, 25nm and 30nm. I'm confused by this. Can someone care to explain?

"The RLAT Track will have half-degree latitude separation with the two tracks beside it. In other words, it will be spaced 30nm from the tracks to the north and south of it."

"Reduced Lateral Separation Minimum (RLatSM) is the implementation of 25nm lateral separation standards in North Atlantic High Level Airspace (HLA) (Minimum Navigation Performance Airspace (MNPS)) for qualified aircraft flying within the Organised Track System (OTS)."

"RLongSM (5 minutes longitudinal) and RLatSM (23 NM lateral on. ½ degree tracks in NAT Organized Track System"

[eckhard]

1/2 degree latitude is only 30nm when the parallel tracks are aligned exactly east/west. Any other compass direction will reduce the lateral separation, as measured at right angles to the tracks in question. Somebody cleverer than me will provide a suitable formula, involving trig functions.

[Banana Joe]

Ch of Long*Cos(Lat).
It's been a while since I've done GNAV and even that was a simplified version of the actual subject. So I stand to be corrected.

[BBK]

rudestuff

It’s not that simple as eckhard has explained. Perhaps you need to do the reading up? For the OP the SLOP can be 0, 1 or 2 nm right of track. Of course for weather deviations then left or right. Hope that helps.

[MarkerInbound]

A 2019 revision to NAT Doc 007 says you can offset in tenth of a mile increments if your aircraft is capable of doing so.