SLOP Strategic Lateral Offset Procedure

[Engineer]

Just wondering how many of you guys/ladies apply this procedures in oceanic (especially NAT) and remote airspaces?
Also if applied how long have you used it for?
Cheers :D

[Pub User]

Yes, occasionally, if it seems appropriate with the traffic & wind situation.

It was promulgated as a 'normal' procedure in about Nov 05, but took around 6 months or so to trickle into our Ops Manual.

[Brain Potter]

Our lot made it mandatory to select either 1 or 2 nm right SLOP about a year ago. This is applicable in NAT airspace.

[K.Whyjelly]

As a tool to assist in increasing the safety margins in MNPS airspace by distributing aircraft laterally and equally across 3 available positions (centrline, 1R and 2R) I tend to offset on every sector that I am PF. Before applying the offset I apply a bit of common sense and try to see what other aircraft on my track are doing by using TCAS and the good old Mk1. It is reassuring to see those other contrails way off to the left of me.

NATS figures for aircraft in the Eastern portion of the North Atlantic show a disappointing frequency of offset by airlines - less than 10% compared to the hoped for 67%. (AT least those were the most up to date figures I could find. Anybody 'in the know', know better)?

Anything that increases your safety and reduces your chances of wake turbulence encounters has to be good, I sometimes even use SLOP on random routes.

Considering applying offset is encouraged by the company and is up to the pilot to apply as he/she sees best.

[Fly3]

I have been using this for the past 18 months or so but I find that few of my colleaques seem to be doing so. Quite a few of them claim never to have heard of it when I suggest that they might like to apply it!

[Jetstream Rider]

I don't really see the need to SLOP if no one else is around. I also think its silly if my aircraft is SLOPPED and the aircraft behind SLOPS too - this happened a while back and a Jumbo went straight underneath us, setting the RAD ALT off. It seems that only 67% of flights should do it when crowded, otherwise no need.

Given that its not usually THAT busy on random routes and even on the NAT tracks, I find I only use it about 1 or 2 in 10 times, so maybe 10% isn't too bad?

[Henry VIII]

Always 1R since the implementation in NAT area.
For other areas refer also to this thread (http://www.pprune.org/forums/showthread.php?t=262739&highlight=slop).
HVIII

[proxypilot]

As Jetstream Rider says surely if everyone uses SLOP and crosses at 2R it defeats the purpose??

[Fly3]

I think some people might be missing the point here. The objective of the procedure is to re-introduce the randomness of tracking which was common in the "old days" before GPS etc. SLOPS suggests that each pilot changes his tracking every crossing. Say on centreline first time, 1nm right next time and 2nm right third time. If everyone does this then the likelyhood of having a Rad Alt tripped by an underflying B747 for instance is significantly reduced as is the risk of a head on with opposite direction traffic.

[topper28]

Never done it NAT, but I always use SLOP overflying Africa

[ARINC]

Feature available on both Boeing and Scarebus FMC/MCDU
Says it all...note randomness comments.

http://www.scottipc.com/course/content/view/37/61/

[None]

For my company:

Mandatory in Africa
Recommended in South America
should consider for NATS

I was under the impression that SLOP was very helpful concerning opposite direction traffic, and not so much for same direction traffic.

The rate of closure for nearly same direction traffic gives me more time to detect, analyze, and take preventive action compared to opposite direction traffic.

There is always that occasional jet that did not show up on TCAS. SLOP proves its benefit when he goes by 2 or 3 miles off the left wing.

[FE Hoppy]

From the IFALPA Safety Bulletin june 06:

SLOP – Strategic Lateral Offset Procedure
1. Crews should be aware of this procedure for use in
oceanic and remote airspace. SLOP should be a SOP, not a
contingency, and operators should be endorsing the use of
lateral offsets for safety reasons on all oceanic and remote
airspace flights.
2. Crews should be aware of the “coast-out to coast-in”
operational use of the procedure.
3. Crews should only offset 1 nm or 2 nm RIGHT of
centerline.
NOTE: Operators are reminded that the current SLOP is
designed to mitigate the effects of wake turbulence as well
as to enhance flight safety.


And from the IATA Oceanic Errors Safety Bulletin - Ed. 2, 2006
Strategic Lateral Offset Procedure (SLOP):
• With widespread use of GPS, lateral navigation accuracy on the OTS has increased significantly. Ironically,
there has been a corresponding increase in the probability of critical traffic conflicts resulting from large height
deviations. SLOP is designed to enhance flight safety by reintroducing a degree of randomness among aircraft
flying the OTS..
• SLOP does not require an ATC clearance. It is not necessary to advise ATC of the offset flown
• Crews should only offset 1 nm or 2 nm RIGHT of centerline.
• The FMS must be used to program the offset, with LNAV used to maintain the offset course.
• Use SLOP procedures for wake turbulence or weather avoidance at 1nm or 2nm intervals RIGHT of track
• SLOP is SOP, not a contingency. Operators should endorse the use of lateral offsets for safety reasons in all
oceanic and remote airspace flights where implemented.
• The decision to fly an offset should be determined to benefit in randomly distributing traffic. TCAS may be used
to determine the best lateral offset to achieve randomization with other traffic or for wake turbulence avoidance.
• Ensure a return to track centre-line prior to Oceanic Exit point.

I'm sure the current versions have more to say but this was the last time I gave an RVSM/MNPS course.

[CI100]

The best way to do it is to check the Jepp section for the country you are flying in first, not all airways are permitting SLOP procedure.

Ex. India is one, only few track can do SLOP. mainly over indian/oman sea.

[wjanicki]

I've only seen published procedures for SLOP in Oceanic flight. Are there local regulations in Africa and South America that allow for this?

[JimR]

It has been commented that flying an offset track can improve the odds of avoiding collisions due to the extreme accuracy of navigation systems now. From reading SLOP procedures it would appear that the selected offset is either on-track, 1 nm or 2nm to the right, although I note that there are proposals for other offsets. This seems strange in that I thought the idea was to simulate past generations inherent lack of airway precision. Would it not be more appropriate that the system (or PF) introduce a random (but fixed) right offset during the on-route portion of the flight, lets say between 0 and 2 nm. Can anybody comment as to why specified offsets are preferred?
I realize this is an old thread but seemed the logical place to post.

[King Muppet]

No reason, I suppose. Except that my FMC only allows increments of whole nautical miles...

[TO MEMO]

I always do!

Reccomend watching this video about SLOP, done by NAT PCO.

YouTube - Slop (http://www.youtube.com/watch?v=g_a8bZGxaCc)

Cheers!

[DA-10mm]

topper28...

always in africa...you never know what you're gonna get.
so always offset.

I've seen more horror-stories of "african carriers" trying to kill us on a regular basis climbing too quickly.

[Panama Jack]

AS CI100 points out, in Indian airspace it is only permitted in the "Oceanic" airspace, which is where it plays an additional risk reduction benefit due to the often poor HF radio quality/accessibility with Indian ATC.

In China, ATC typically instructs us to offset 2nm right of track as part of their RVSM program. Seems like a very sensible procedure to reduce risks inherent with the complex China RVSM procedures.

To me, SLOP seems like a very sensible procedure on two-way airways-- it applies the "rules of the road" where you drive on the right hand side of the centerline of the street (at least in progressive, civilized countries :E ), rather than on the exact center of the roadway with the logic that being equidistant from the pavement edge is the safest way to go.

[wonwinlow]

I think SLOP should be used on a regular basis, specially on the NATS, but never use the same offset as your colleague above or below, occasional severe turbulence might bring both aircraft mighty close to each other, 1000' is not too much for these TCAS jumpy A/C.

[JimR]

Thanks guys. My original thought though was why not select a truly random offset to the right, for instance 1.7 nm, rather than 0, 1 or 2 nm?

[PappyJ]

I've only seen published procedures for SLOP in Oceanic flight.


China permits up to 3 miles RIGHT with no ATC clearance required (See Jep manual). But, with their recent implementation (last year) of RVSM, the ATC in China is regularly issuing off-set instructions when more than 2 aircraft within 100 miles of each other (different levels). Most believe there's a bit of a ATC fear factor involved.