SLOP (Strategic Lateral Offset Procedure)
 

Every time I fly in a non-radar environment I prefer to set an offset to the right of the airway. Sometimes even in “radar” environment (in some countries) I opt for R0.1.

Just had an argument in the cockpit about it. The other guy believes that it is "to look for trouble" to set even a quarter mile offset in non-radar environment flying over the East Africa's best: Tanzania, Kenya, Somalia, Yemen.

Your fellow pilot clearly has an acute lack of imagination and will to live. Everyone with a spot of self-preservation does it - the Legacy-vs-73 over Brazil in non-radar environment wouldn't have happened if one of the 2 crews had SLOP'ed.

If I were you, I'd just keep on doing what you're doing now, live long and prosper ;)

In my outfit, SLOP = 2nm right. SOP.

The airspace wherein this is done is defined in our manuals.

Of course, you can only fly safe if the other guy does too. While happily SLOP'ing in SE Asia, another aircraft went precisely over the top of us.

We asked how come he was out there? The answer was "If every body is flying 1.0nm right, I'll fly 1.nm left and keep out of their way." This guy was a Captain for a major flag carrier!!:sad:

Yep, stay safe out there!!

G'day ;)

Are you saying that everyone should fly a SLOP? How would that stop any mid-air crash if everyone is doing it?!? How do you know who is or isn't? I suppose that the usual position reports, especially over Africa, might provide some clues, if you mention it. If everyone does it then what is the difference of everyone being directly on the airway?

Xfeed,

It will definitely stop the head on collisions from opposite direction traffic, same direction (climbing or descending) and crossing traffic is a different story. So I am not sure it will work in all the situations, but than again we also have the TCAS to rely on.

In Chinese airspace ATC wants you to offset 2R. Of course as soon as we leave Chinese airspace we are back to normal flight plan routing.

This is what MNPS Operations Manual has to say about SLOP:

Strategic Lateral Offset Procedures (SLOP)

8.5.1 ATC clearances are designed to ensure that separation standards are continually maintained for all traffic. However, the chain of clearance definition, delivery and execution involves a series of technical system processes and human actions. Errors are very rare but they do occur. Neither pilots nor controllers are infallible. Gross Navigation Errors (usually involving whole latitude degree mistakes in route waypoints) are made, and aircraft are sometimes flown at flight levels other than those expected by the controller. When such errors are made, ironically, the extreme accuracies of modern navigation and height keeping systems themselves increase the risk of an actual collision. Within an SSR environment the controller is alerted to such errors and can, using VHF voice communications, intervene in a timely fashion. This is not the case in Oceanic airspace, such as the North Atlantic, where the controller’s awareness of traffic disposition is reliant largely upon pilot voice position reports and communications utilise HF or SATCOM Voice through a third party radio operator. Consequently, it has been determined that allowing aircraft conducting oceanic flight to fly self-selected lateral offsets will provide an additional safety margin and mitigate the risk of traffic conflict when non-normal events such as aircraft navigation errors, height deviation errors and turbulence induced altitude-keeping errors do occur. Collision risk is significantly reduced by application of these offsets. These procedures are known as “Strategic Lateral Offset Procedures (SLOP)”.

8.5.2 This procedure provides for offsets within the following guidelines:

a) Along a route or track there will be three positions that an aircraft may fly: centreline or one or two miles right

b) offsets will not exceed 2 NM right of centreline

c) and offsets left of centreline must not be made


8.5.3 Distributing aircraft laterally and equally across the three available positions adds an additional safety margin and reduces collision risk. This is now a standard operating procedure for the entire NAT Region and pilots are required to adopt this procedure as is appropriate. In this connection, it should be noted thaDistributing aircraft laterally and equally across the three available positions adds an

a) Aircraft without automatic offset programming capability must fly the centreline.

b) Operators capable of programming automatic offsets may fly the centreline or offset one or two nautical miles right of centreline to obtain lateral spacing from nearby aircraft. An aircraft overtaking another aircraft should offset within the confines of this procedure, if capable, so as to create the least amount of wake turbulence for the aircraft being overtaken.

c) Pilots should use whatever means are available (e.g. TCAS, communications, visual acquisition, GPWS) to determine the best flight path to fly.

d) For wake turbulence purposes, pilots should also fly one of the three positions shown above. Pilots should not offset to the left of centreline nor offset more than 2 NM right of centreline. Pilots may contact other aircraft on the air-to-air channel, 123.45 MHz, as necessary; to co- ordinate the best wake turbulence mutual offset option. (Note. It is recognised that the pilot will use his/her judgement to determine the action most appropriate to any given situation and that the pilot has the final authority and responsibility for the safe operations of the aeroplane. See also Chapter 11, paragraph 11.5.) As indicated below, contact with ATC is not required.

e) Pilots may apply an offset outbound at the oceanic entry point and must return to centreline prior to the oceanic exit point.

f) Aircraft transiting radar-controlled airspace mid-ocean should remain on their already established offset positions.

g) There is no ATC clearance required for this procedure and it is not necessary that ATC be advised.

h) Voice Position reports should be based on the waypoints of the current ATC clearance and not the offset positions.

I'm a big fan of SLOP. 1nm right on the Airbus.
However be careful with Australia. Outside of 200nm off the coast there is no need for ATC approval but inside that area you must have ATC clearance and the Australians can be a bit touchy when it comes to things not being done there way. (Before you aussies have a go, I'm an aussie, ex GA, Skywest and Ansett 95-01, so I'm entitled to comment.)

SLOP...never found it necessary, and neither have the Captains that work for us, either.
Therefore, not done in our outfit....and, not likely to start anytime soon.

411A, you won't find it necessary in the future either if you meet opposite direction traffic same level, same track, non-slopped.
A tiny possibility perhaps, but nonetheless a tiny fix that could someday have a massive payoff. You say why, I say why not?

Ah, but you were doing it in the past, in pre-GPS days. The lateral navigation errors inherent in the old systems added a bit of "dither" to your position. Now we all fly *exactly* the same track between waypoints and if someone is coming the other way at the wrong level using their super-accurate RVSM-certified altimetry, you're almost certain to collide. An offset to the right mitigates against this (admittedly rare) scenario.

Why not to do it? Can't really think of any good reason...

Aren't you required to offset right and comply with the In-Flight Broadcast Procedure in that airspace?

I SLOPd 50% of the time on Oceanic Tango routes to the Canaries. Law of averages I suppose trying to reduce the risk of collision. Arguments valid for both techniques.

It is, of course, supposed to be a "random" offset of either 0, 1 or 2 miles, but it is easy to fall into a routine after a while. A good friend of mine has a novel technique for insuring the requisite element of randomness. While riding on his jumpseat to London a couple of years ago, I was intrigued when, as we approached coast out, he picked up the handset and called the no. 1 flight attendant. He gets her on the phone and asks her to pick a number between 1 and 3. She picks a number, having absolutely no idea what he's doing, then he hangs up, turns around to me and says, "Can't get any more random that that..." He then says, "You have to ask them to pick something from 1 to 3. If you ask for something from 0 to 2, they always pick 0. So just take one off whatever they choose, and you're all set."

Except if the flight attendant happens to be a maths or computer science graduate, or a regular visitor of xkcd. :)

9 points:

While you do not need permission to SLOP outside 200 nm of Oz, you need to ADVISE them, which I found out to my own cost! I'm still trying to work out the semantics to this day, I think it is because their ADS-C track deviation monitoring is set to 1 metre :hmm:

What about FAR 91.181?

Sec. 91.181

Course to be flown.

Unless otherwise authorized by ATC, no person may operate an aircraft within controlled airspace under IFR except as follows:
(a) On a Federal airway, along the centerline of that airway.
(b) On any other route, along the direct course between the navigational aids or fixes defining that route. However, this section does not prohibit maneuvering the aircraft to pass well clear of other air traffic or the maneuvering of the aircraft in VFR conditions to clear the intended flight
path both before and during climb or descent.

Feather # 3.
Saw a major flag carrier do the same "opposite" offset on the OTS. Can't understand the logic!
Always use SLOP as per SOP myself. Shame it wasn't used in Brazil.

We use it, as recommended, in the IFBP area in Africa - that's most of it! Works well especially as our company often flight plans the northbound and southbound a/c on the same airway, not that there are may to choose from. It's much nice, and safer, to see the other guys 1000'/4nm away rather than 1000' directly above or below.

On the North Atlantic tracks it's less clear if there is any benefit unless you are in proximity to someone else. However, our company suggests an offset, or not, so I tend to go with the plan. Put it this way, if something did happen and I hadn't offset the first question, over tea and biccies, would be why not. Apparently it's what Nav Canada and Shanwick like to see.