Tag: SLOP

Why, How and Where should you SLOP?

In Short: Strategic Lateral Offset Procedures (SLOP) costs nothing and increases flight safety. If the airspace permits it, you should be “randomly” offsetting, especially across the North Atlantic. Left is for losers – don’t SLOP left of track.

We had a discussion in OpsGroup recently about SLOP (Strategic Lateral Offset Procedures) and it elicited some interesting responses, as well as some confusion.

So – Why, How and Where should you SLOP?

Why?

GPS technology allows modern jets to fly very accurately, too accurately it turns out sometimes! Aircraft can now essentially fly EXACTLY over an airway/track laterally (think less than 0.05NM), separated only by 1000FT vertically. A risk mitigation strategy was proposed over non-radar airspace to allow pilots to fly 1-2 nautical miles laterally offset from their track, randomly, to increase flight safety in case of any vertical separation breakdown.

How did we get here?

Navigation paradox

What we just described is known as the navigation paradox. The research shows that “increases in navigational precision” actually increases the collision risk – huh?

Here are some interesting stats to consider:

  • In a simulation, aircraft cruising at random altitudes have five times fewer collisions.
  • During a 2000 study, it was shown that hemispherical cruising altitude rules resulted in six times more mid-air collisions than random cruising altitude non compliance.
  • If more randomness was applied to the hemispherical cruising level model, the navigational paradox risk could have been largely reduced and up to 30 midair collisions avoided (up to 2006). Including the tragic GOL 2006 accident.

So we get it; the rules of the air, sometimes inject risk to flight safety due to their lack of randomness.

A way to reduce risk and inject randomness?

It was 2004 when SLOP was adopted in the most congested non-radar airspace in the world, namely the North Atlantic.

Although the Navigation Paradox is the reason SLOP was introduced and continues to be implemented, there are some nice risk mitigation side-effects too: wake turbulence reduction (at times), contingency buffers if you experience severe turbulence and can’t maintain altitude (“level busts”), etc.

SLOP therefore reduces the risk between traffic which is not operating in accordance with the correct air traffic control clearance or where an error has been made in the issue of an air traffic control clearance.

Still, there is a large number (>40%) of aircraft not adopting these procedures even though they are now mandatory on the NAT.

If >40% of pilots are using SLOP 0 (meaning no offset at all), what does that matter? That means half the flights are operating over the same lateral paths and all it takes is one minor vertical deviation for there to be a significant loss of separation.

The daily NAT track message always reminds pilots to employ SLOP procedures:

FOR STRATEGIC LATERAL OFFSET AND CONTINGENCY PROCEDURES FOR OPS IN NAT FLOW REFER TO NAT PROGRAMME COORDINATION WEBSITE WWW.PARIS.ICAO.INT.
SLOP SHOULD BE STANDARD PROCEDURE, NOT JUST FOR AVOIDING WX/TURB.
How should you SLOP?

Consider some best practice advice:

  • LEFT IS FOR LOSERSnever offset LEFT. On bi-directional routes a LEFT offset will INCREASE collision risk rather than decrease it. There are areas in the NAT Region where bi-directional traffic flows are routinely used. And there are times when opposite direction traffic may be encountered in any part of the Region. Once upon a time (between introduction of RVSM and pre-SLOP, it was ok to go LEFT, not anymore!)The only exception would be in certain airspace where ATC request you to SLOP LEFT (e.g. China).
  • The system works best when every 2 out of 3 crossings you fly, you apply an offset. Shanwick says this generally means at least 1 out of 3 aircraft are slopping.
  • You don’t need to ask ATC for approval; you can SLOP from the NAT entry point to the NAT exit point.
  • Only offset if your FMC has the function to do so – do not do it manually.
  • Good airmanship applies here. What’s happening around you? Who is above, below and near you on the same track. Co-ordinate on 123.45 if needed.
  • 2nm RIGHT is the maximum approved SLOP.
  • Flip a coin to decide like some do! Captain is PF? 1R going west; First Officer 2R going east etc. Studies show that on the NAT, 40% do 1R and only 20% go 2R. Don’t be afraid to go the full 2R!
  • If you are overtaking someone, the ICAO guidance in NAT DOC 007 is to apply SLOP so as to create the “least amount of wake turbulence for the aircraft being overtaken”.

Where though?

Our friend Eddie at Code 7700 gave a great comprehensive list so here it is verbatim.

  • Africa, almost all remote locations employ SLOP. Check the Jeppesen Airways Manual / Air Traffic Control / State Rules and Procedures – Africa) to be sure. Rule of thumb: if you are in radar contact, you probably should not SLOP.
    • One notable exception where they don’t want you to SLOP is in the HKNA/Nairobi FIR. The AIP states: “SLOP is not applicable in the Nairobi FIR due to efficient surveillance and communication systems.” (We do remind you however that recently in the Nairobi FIR, a 767 and 737, both at FL370 came a little too close for comfort).
  • Australia is another special case. You may only offset in the OCA, and, if you’re still on radar, then you need to tell ATC, both when starting the offset, or changing it. Within domestic CTA airspace, you must fly centerline. (According to Australian guidance in Jeppesen Pages).
  • China, on routes A1, L642, M771, and N892 (according to China guidance in Jeppesen Pages). In some areas they employ their unique SLOP offsets, but do allow the standard 1 nm and 2 nm offsets.
  • New York, Oakland and Anchorage Oceanic FIRs (according to U.S. FAA guidance).
  • Oceanic airspace in the San Juan FIR (according to U.S. FAA guidance).
  • North Atlantic Track Region: SLOP is mandatory (according to the North Atlantic Operations and Airspace Manual).
  • The Pacific (including the NOPAC, Central East Pacific (CEP) and Pacific Organized Track System (PACOTS) (according to U.S. FAA guidance).
  • South Pacific airspaces (according to U.S. FAA guidance).
FAQ:
  • Should I SLOP crossing the Atlantic even if I’m on a random route or above the published NAT FL’s?

Yes! You should especially do it then. There is a higher chance of opposite direction traffic. That extra mile or two (randomly selected of course) could be a life saver!

  • What about micro-slop?

That is lateral offsets between 0 and 1 nm (0.1 etc). ICAO mentions “LOP provisions as specified in ICAO PANS-ATM Doc.4444 were amended 13 November 2014 to include the use of “micro-offsets” of 0.1 Nms for those aircraft with this FMS capability. Appropriate guidance for the use of this amended procedure in the North Atlantic is under study and hence pending.”

We have been advised that the USAF is doing this trial over the NAT in the coming months but at this stage it is NOT APPROVED. Most FMC systems can’t micro-offset yet anyway.


We might have missed something or maybe we didn’t cover your specific question?

Drop us a line and will do our best to answer.

Bottom line, SLOP costs nothing but increases flight safety.

The Impact of Space-Based ADS-B on International Operations

I can distinctly remember the build up to and roll out of GPS navigations systems. Like so many of us, I was excited to see this new technology integrated into my cockpit. The idea that I would have the capability to accurately determine my position anywhere in the world was exciting!

It’s hard to overstate the significance of GPS navigation on the international operation of aircraft, particularly when operating in oceanic airspace. Today we are about to reach a similar milestone that could be even more significant – the introduction of a Space-Based Automatic Dependent Surveillance Broadcast (SB ADS-B) monitoring system.

When SB ADS-B completes its deployment (scheduled 30 December 2018), we will achieve worldwide, pole-to-pole surveillance of aircraft. This goes beyond a pilot knowing his or her own location. This opens up the ability for ATC to locate any ADS-B equipped aircraft anywhere in the world. With the US and EU ADS-B requirements approaching in 2020, aircraft that operate internationally will almost certainly be ADS-B equipped.

A brief history of Space-Based ADS-B

SB ADS-B technology has been placed into service by a commercial company, Aireon, and not a governmental entity, which has enabled it to be brought to operational status in a much shorter timeline than most other government implementations.

Although Aireon was initially established in 2012 to provide civilian surveillance services, the disappearance of Malaysia Flight 370 changed the industry. The inability to locate the aircraft forced industry regulators to consider how improved aircraft tracking might have helped to resolve the location of the aircraft in distress and prevent a future disaster. In response to this concern, ICAO created a standard for aircraft tracking designated as the Global Aeronautical Distress Safety System (GADSS). Aireon responded by creating a low-cost tracking solution based on aircraft ADS-B equipage utilizing the SB ADS-B network to meet that tracking requirement faster and cheaper than many of the alternatives.

This implementation takes advantage of the same ADS-B 1090ES systems already installed in most aircraft, not requiring any additional investment or modification from operators who currently comply with ICAO ADS-B approved 1090ES systems. Compare this to the evolving and evasive FANS 1/A+ requirements that have placed many operators in the position of having to upgrade aircraft (at great expense) only to find they are not PBCS and/or U.S. domestic compliant. Quite a contrast.

What are the benefits?

The primary advantage of the introduction of surveillance into oceanic operations will be a reduction in separation. Initially, this will be applied to in-trail spacing (longitudinal separation) and potentially reduce that separation to as close as 14 Nautical Miles (NM). The current longitudinal standard for data link approved aircraft is 5 minutes or approximately 50NM. The introduction would significantly increase the capacity of the most fuel-efficient routes and altitudes. The trial implementation is not expected to be restricted to specified tracks or altitudes, just between properly equipped aircraft.

Another key advantage of SB ADS-B is that the system is based on an active constellation of 66 low earth orbit satellites with geo-synchronous orbits that provide worldwide coverage. The system will also have 9 backup satellites available in orbit as well. The information on worldwide aircraft location will be in the system, it’s just a matter of having it sent to ATC control panels that are properly equipped to display the information. The SB ADS-B system operates independently from the ADS-B ground stations and can provide a direct data feed to air navigation service providers (ANSPs).

The primary targets for Aireon SB ADS-B services are ANSPs such as the FAA, EASA, Africa’s ASECNA, South Africa, New Zealand, Singapore, etc. This brings tremendous value to areas like Africa and Southeast Asia where ANSP’s face unique challenges involving infrastructure. Placing a network of ground-based ADS-B receivers in remote areas can expose them to vandalism or theft. As an example, a recently installed ILS system in Benin, Nigeria was stolen!

What does my aircraft need to be compliant?

In order for SB ADS-B separation reduction to be applied, aircraft will be required to be ADS-B and fully PBCS compliant. The controlling agency will determine eligibility based on the flight plan filing codes for ADS-B and PBCS. Let’s recall that the PBCS requires FANS 1/A+ approval with RCP240, RSP180, and RNP 4 capabilities. Just add ADS-B, NAT HLA, and RVSM equipage and approval and you’re ready! That is a lot of approvals, plus let’s not forget, TCAS Version 7.1 and Enhanced Mode S Transponder equipage is required as well.

Where will it be implemented?

Initial trial use of SB ADS-B for surveillance and separation will begin in Canada’s Edmonton Flight Information Region (FIR) in the first quarter of 2019. This will be followed by a planned trial launch in the North Atlantic (NAT) on 29 March 2019. The NAT oceanic surveillance trial program will be employed in both in Gander and Shanwick’s oceanic FIRs. Santa Maria will also introduce ADS-B separation standards, but that program will initially be limited to ground-based ADS-B operations.

We anticipate a mid-December 2018 release of a North Atlantic Ops Bulletin detailing the trial implementation which will be referred to as “Advanced Surveillance-Enhanced Procedural Separation” (ASEPS). This is to be followed by ICAO publishing the associated standards for ASEPS in a 5 November 2019 update to Procedures for Air Navigation Services – Air Traffic Management (PANS-ATM) Document 4444. This would move the ASEPS program beyond trial use and allow implementation of ASEPS based operations worldwide.

The final specifics involved in the trial program will be detailed in Canadian and United Kingdom Aeronautical Information Publications (AIPs), most likely involving a release of Aeronautical Information Circulars (AICs) to formally initiate the trial programs.

The NAT HLA does not anticipate requiring ADS-B for airspace entry but simply employing it as available. The impending U.S. and EU ADS-B requirements in 2020 will help ensure common equipage.

The introduction of ASEPS reduced separation standards in oceanic and remote regions will also impact contingency procedures for operators in the NAT HLA. To address this concern ICAO has created new contingency procedures for oceanic and remote operations which will also be identified in the November 2019 update to Procedures for Air Navigation Services – Air Traffic Management (PANS-ATM) Document 4444.

We expect the mid-December release of an additional North Atlantic Ops Bulletin detailing the trial implementation of these new contingency procedures in the NAT HLA airspace to be implemented with ASEPS. These new contingency procedures will initially only be used in the NAT HLA but, after the ICAO approval in November 2019, they may be implemented in other oceanic regions as well.

It would be important to note that the ASEPS target date for implementation, 29 March 2019, is also the target date for the expansion of the PBCS tracks in the North Atlantic Organized Track System. Add in the change in contingency procedures and that is a lot of moving parts, all happening at the same time, in the most congested oceanic airspace in the world.

One thing we don’t anticipate changing on March 2019 is strategic lateral offset procedures (SLOP). Changes may follow down the road but it’s not on the calendar now.

Let’s all get ready for a busy spring in the North Atlantic!

Mitch Launius is an International Procedures Instructor Pilot with 30West IP and can be contacted through his website: www.30westip.com

My first North Atlantic Flight is tomorrow – NAT Ops Guide (Updated 2018)

For the latest changes and updates on the North Atlantic, including our most recent Guides and Charts, use our NAT reference page at flightservicebureau.org/NAT.

Of all the hundreds of questions we see in OPSGROUP, one region stands out as the most asked about – the NAT/North Atlantic. So, we made one of our legendary guides, to get everything into one PDF.  It’s called “My first North Atlantic Flight is tomorrow” – and now we’ve updated it for 2018!

Contents:

  • 1. What’s different about the NAT?
  • 2. Changes in 2018, 2017, 2016, 2015
  • 3. NAT Quick Map – Gander boundary, Shanwick boundary
  • 4. Routine Flight Example #1 – Brussels to JFK (up at 5.45am)

  • 5. Non Routine-Flights: No RVSM, No RNP4, No HF, 1 LRNS, No HLA, No ETOPS, No TCAS, No Datalink – what you can do and where you can go
  • 6. Diversion Airports guide: Narsarsuaq, Sondy, Kef, Glasgow, Dublin, Shannon, Lajes, Fro Bay, Goose Bay, Gander, St. Johns
  • 7. Airport data
  • 8. Overflight permits – routine and special

  • 9. Special NAT procedures: Mach number technique, SLOP, Comms, Oceanic Transition Areas, A successful exit, Screwing it up, Departing from Close Airports
  • 10. North Atlantic ATC contacts for Shanwick, Gander, Iceland, Bodo, Santa Maria, New York – ATC Phone, Radio Station Phone, AFTN, Satcom, CPDLC Logon codes; and adjoining Domestic ATC units – US, Canada, Europe.
  • 11. NAT FPL Codes
  • 12. NAT Flight Levels
  • 13. Flight Plan Filing Addresses by FIR
  • 14. Links, Questions, Guidance

Excerpt from the Routine Flight #1:

 

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  1. OPSGROUP Members, login to the Dashboard and find it under “Publications > Guides”. All FSB content like this is included in your membership, or
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This is what an Airbus 380 looks like when it’s coming to get you

  • New guidance issued to OpsGroup by Flight Service Bureau
  • New warnings to be issued by Air Traffic Controllers – EASA SIB to follow
  • Updated 2017 SLOP offset procedures


With the A380 vs Challenger 604 incident,
there is now growing concern amongst aircrews about the effects of the A380’s wake turbulence.

In this incident, reported by the Aviation Herald, a Challenger 604 at FL340 operating from Male-Abu Dhabi passed an A380 opposite direction at FL350, one thousand feet above, about 630nm southeast of Muscat, Oman, over the Arabian Sea. A short time later (1-2 minutes) the aircraft encountered wake turbulence sending the aircraft into an uncontrolled roll, turning the aircraft around at least 3 times (possibly even 5 times), both engines flamed out, the aircraft lost about 10,000 feet until the crew was able to recover the aircraft, restart the engines and divert to Muscat. The aircraft received damage beyond repair due to the G-forces, and was written off.

This is a recovery that is in the same category as the ‘Miracle on the Hudson’, and the DHL A-300 recovery in Baghdad. Envision the alternate scenario, which was far more likely: Challenger 604 business jet missing in remote part of the Indian Ocean. Last contact with was a HF radio check with Mumbai. No recent satellite logons. Position uncertain. Search and Rescue attempt called off after 15 days. Nothing found. Probable cause: flew into CB.

Thanks to the remarkable job by the crew, we don’t have to guess. We know what happened. And now, there are questions.

We’ve seen this story before

Back in 1992/3, two back-to-back fatal crashes (a Citation, and a Westwind) were attributed to the unusual wake turbulence pattern of the Boeing 757. In fact, at the time, NOAA said it was the most intense wake they had ever seen. In December 1993, the FAA told controllers to increase the separation, and warn aircraft following a 757 of its presence.

This was 10 years after entry into service of the 757, which had its first revenue flight in 1983.

Sound familiar? The A380 had its first revenue flight in 2007. We are 10 years down the track, and it’s very tempting to apply the logic that because this degree of incident hasn’t happened before, it’s a one-off. An outlier. That the crew reacted erroneously to a small wake upset at the limit of their flight envelope. This is both unlikely, and, given the potential threat to other crews, a dangerous perspective.

The last review of A380 wake turbulence was done in 2006, primarily by Airbus. As a result, a new category was required – “Super“, in addition to the existing Light, Medium, and Heavy, for use by controllers when applying the minimum separation on approach and departure. However, no additional considerations were applied for enroute wake turbulence.

Most pointedly, the review concluded that the A380 did not need any wake turbulence separation itself, because of its size. The A380 is the only aircraft in the world to have this “out”. It’s a beast. Even an Antonov 124 or Boeing 747 needs 4nm from the traffic ahead.

New guidance

Given the incident, the similarity to the B757 story, and that quiet pointers towards a bigger risk, Flight Service Bureau has issued guidance to OpsGroup members, in Note to Members #24 (March 19th, 2017), which can be downloaded publicly here. The highlights are:

  • As Aircrew, use SLOP whenever you can.
  • As Controllers, be mindful of smaller aircraft passing underneath A380’s.
  • Avoid flying the centreline if you can. SLOP 0 is not an offset. Choose 1nm or 2nm.
  • Note the new SLOP rules from ICAO in the 16th edition of Doc 4444.
  • Expect guidance from EASA and the FAA to follow

With very recent updates to both NAT Doc 007 and ICAO Doc 4444, the rules for SLOP are a little different than before.

Download the OPSGROUP Note to Members #24 – Enroute Wake Turbulence.

 

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