Beware of the A380

[Chaxterium]

one of the three available options (centre line, 1.85 km (1 NM) or 3.7 km (2 NM) right offset) may be used.

Perhaps this is what confused me.

[complexintentions]

Nope. Centreline is definitely one of the options in SLOP. Otherwise you are mathematically increasing the chance of collision, by reducing the options from three to two. Think about it. If EVERYONE flew either 1 or 2 miles offset, you would have a 50/50 chance of being on the same offset. With centreline included that reduces to 1 in 3.

However, the key to remember is that 2 out of every three flights need to be offset either 1 or 2 miles right of track for the randomization to work.

The wording of the ICAO doc is poor, but the "three available options" is not just for wake turbulence. This according to a Shanwick controller and my EASA guru. It's certainly the correct answer on the EASA exam so apparently that's what the regulator thinks!

2. Definition
The strategic lateral offset shall be established parallel to the designated ATS route at a distance of 1.85 km (1 NM) or 3.7 km (2 NM) to the RIGHT of the centre line relative to the direction of flight.

These two track options (1NM and 2NM) become available in addition to the track centre line, not instead of it.

[complexintentions]

Here's a more complete reference (bolding is mine):

Source: NAT Doc 007, North Atlantic Operations and Airspace Manual, 2017 edition.

8.5.3

Distributing aircraft laterally and equally across the three available positions adds an additional safety margin and reduces collision risk. SLOP 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 that:

a) Aircraft without automatic offset programming capability must fly the centreline.
b) To achieve an equal distribution of flying the centreline or 1 NM (one nautical mile) right or 2 NM (two nautical miles) right of centerline, it is recommended that pilots of aircraft capable of programming automatic offsets should randomly select flying centreline or an offset. (See Note in 8.5.2 a) above) In order to obtain lateral spacing from nearby aircraft (i.e. those immediately above and/or below), pilots should use whatever means are available (e.g. ACAS/TCAS, communications, visual acquisition, GPWS) to determine the best flight path to fly.
c) 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.
d) For wake turbulence purposes, pilots should 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 recognized 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 13, paragraph 13.5.) 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 unless otherwise authorized by the appropriate ATS authority or directed by the appropriate ATC unit.
f) Aircraft transiting ATS Surveillance-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.

8.5.4

SLOP has been implemented as a standard operating procedure in the NAT Region since 2004. An indication of the proportion of pilots adopting a SLOP offset here is obtained through study of ADS-C position reports. Such study has shown that during 2012 more than 40% of aircraft flying in the NAT MNPS Airspace selected the 1NM Right option and about 20% chose the 2NM Right option. As indicated above, system safety would be further enhanced if aircraft were more evenly distributed between the centreline, 1 and 2 NM Right options. As proposed in paragraph 8.5.3 b) above, Pilots should attempt to determine the offsets (if any) being flown by aircraft immediately ahead on the same track one flight level above and one flight level below. And then select an offset which differs from those. If this is not possible or practical, then pilots should randomly choose one of the three flight path options.

Not trying to be a dick but there's just too much misinformation being spread and reducing your options by 1/3 is not great.

Chaxterium is completely correct. Ahramin and Benwa are not.

[ahramin]

I'm surprised that Shanwick is still using that model as NavCanada Gander gave us guidance several years ago that they recommend all aircraft capable of moving off the centreline should do so when practicable. Our SOP has been changed accordingly. Their point was that the biggest risk of collision is from opposite direction traffic so staying on centreline doesn't reduce risk unless both the speed and altitude of the leading or trailing aircraft is wrong. Thanks for pointing out Doc 007 complexintentions, I didn't realize it still said that.

In any case, you won't find me on the centreline anywhere outside of radar coverage if I can possibly avoid it, you never know when complex is coming through going the other way .

[complexintentions]

"Still" using that model? Like, it's so passé? lol It's a NAT document, not Shanwick-specific. When's the last time you looked at it? There were several significant changes as of January 2017. For example, what's the definition of a gross navigational error?

The whole SLOP concept is to reintroduce randomization which was removed by the accuracy of modern navigation. Reducing that randomization - whether by weighting one's track too much to the centreline OR one of the offsets - is counter to safety. It has always been three choices for that reason. Nothing new, no matter what "Gander said".

In any case, you won't find me on the centreline anywhere outside of radar coverage if I can possibly avoid it, you never know when complex is coming through going the other way.

Why, are you planning to be at the wrong altitude again? lol

We fly random tracks everywhere anyway - more efficient.

[Rockie]

On any given route the only identical track with opposing traffic is the centreline, all the other options utilizing SLOP are offset from each other. So mathematically speaking if collision avoidance is the goal why would you use the only SLOP option common with opposing traffic?

[fish4life]

I don't do long haul overseas stuff so bare with me, if the whole point of SLOP is randomization to help aircraft why don't they just let pilots pick a random distance between 0-2 miles R so one guy can go 1.2 miles another guys picks 1.6 miles etc?

[complexintentions]

On any given route the only identical track with opposing traffic is the centreline, all the other options utilizing SLOP are offset from each other. So mathematically speaking if collision avoidance is the goal why would you use the only SLOP option common with opposing traffic?

Errr...you do realize that the NAT OTS is unidirectional, westbound during the day and eastbound during the night? If you meet someone going the other way there IS a problem! It's also why I find ahramin's Gander recommendation dubious. By far the main threat is from another aircraft going the same direction, (+ wake turbulence or weather) and in that case it's 1 in 3 choices clearly beating 1 in 2. I'm not sure how much more clearly I can put it.

At any rate I am merely quoting the regulatory document. Please direct your questions as to the "why" of NAT SLOP procedures to:

EUROPEAN AND NORTH ATLANTIC OFFICE OF ICAO
International Civil Aviation Organization (ICAO)
European and North Atlantic (EUR/NAT) Office 3 bis, Villa Emile Bergerat
92522, Neuilly-sur-Seine CEDEX FRANCE
e-mail : icaoeurnat@paris.icao.int Tel : +33146418585
Fax : +33146418500
Web : http://www.icao.int/EURNAT/

I'm sure they'd welcome suggestions, too. And then do check back in with the answers, in the spirit of sharing information the way I have.

NATS has made some cool videos visualizing traffic flows. Maybe this will help?

North Atlantic Skies

[Rockie]

On any given route the only identical track with opposing traffic is the centreline, all the other options utilizing SLOP are offset from each other. So mathematically speaking if collision avoidance is the goal why would you use the only SLOP option common with opposing traffic?

Errr...you do realize that the NAT OTS is unidirectional, westbound during the day and eastbound during the night? If you meet someone going the other way there IS a problem! It's also why I find ahramin's Gander recommendation dubious. By far the main threat is from another aircraft going the same direction, (+ wake turbulence or weather) and in that case it's 1 in 3 choices clearly beating 1 in 2. I'm not sure how much more clearly I can put it.

At any rate I am merely quoting the regulatory document. Please direct your questions as to the "why" of NAT SLOP procedures to:

EUROPEAN AND NORTH ATLANTIC OFFICE OF ICAO
International Civil Aviation Organization (ICAO)
European and North Atlantic (EUR/NAT) Office 3 bis, Villa Emile Bergerat
92522, Neuilly-sur-Seine CEDEX FRANCE
e-mail : icaoeurnat@paris.icao.int Tel : +33146418585
Fax : +33146418500
Web : http://www.icao.int/EURNAT/

I'm sure they'd welcome suggestions, too. And then do check back in with the answers, in the spirit of sharing information the way I have.

NATS has made some cool videos visualizing traffic flows. Maybe this will help?

North Atlantic Skies

Having spent much more time on the NAT OTS than I've cared to, yes, I'm quite aware they are unidirectional. Just as I'm sure you're aware most of the world is not the NAT OTS. You also might be aware that SLOP was originally implemented because of fears the extremely accurate navigation capability of GPS also increased the risk of opposite direction traffic collisions since everybody was bang on centreline for the first time in history. Wake turbulence of course was a factor as well, but if it was the only one they would have permitted SLOP right or left to give the most options for avoidance from same direction traffic.

My post was only to point out the obvious flaw in your mathematical logic for collision avoidance. For opposite traffic using SLOP there are a total of 5 possible tracks the airplanes could be on, but only one of them is common for both - the centreline. If I'm going to use SLOP that's the one I'm not going to be on unless I need it for wake avoidance.

[tx'd]

Man us pilots are nerds. Slop this much or slop that much. No wrong or right, just depends what part of the world you're operating in. China has given me everything up to 13 NM right before! So far I've had 2 A380 run ins. One 7 years back in northern Canada 1000 feet above opposite direction. Recently 13 NM in trail vectoring into HongKong. Not a nice sensation! Very sudden large roll and pitching. ATC always as surprised as we are. Will be extra cautious from now on around the big beasts. Lets all remember to report these events properly to help establish reliable data.

[Rockie]

Just to be more nerdy tx'd, what you received from China was an offset which you need a clearance for. SLOP is different, used outside of radar controlled airspace where SLOP procedures are approved, and does not require a specific clearance. It is up to pilot discretion with no clearance or notification to ATC required.

[Heliian]

Regardless, they've known since the design phase of the 380 that it's wake surpasses anything seen before, why such a surprise now? They just don't want to leave the spacing due to congestion and slotting I guess.

[ahramin]

Complexintentions, as others have pointed out NAT OTS is one piece of NAT airspace, and NAT is only one piece of the total oceanic airspace.

The model I'm referring to is the mathematical risk model for collisions in that airspace. Minimum spacing between same level flights is based on a complicated mathematical model which is supposed to take into account all factors and come up with a statistical risk of collision. They have to keep that risk under a certain number (I have no idea how they decide or calculate what that number is). GNE occurrences are plugged into that model and I'm guessing the new definition of GNE to 10 miles helps them keep their numbers ok somehow. Far more interesting in the changes this year are the contingency procedures for emergency descents or drift downs. No one around here seems to have noticed yet, our SOP still allows turn backs.

The risk model includes SLOP, and that's where the "random" 0, 1, or 2 comes in handy mathematically. Staying on centreline "randomly" 1/3 of the time may help with the global statistical risk model for NAT airspace but from a pilot's perspective, the right of track options offer much more safety, especially on bidirectional routes.

Your point about random routes is an interesting one, as I know many pilots who feel SLOP is completely useless on a random route. What I caution them on is that while the route may be random from a NAT OTS perspective, the waypoints themselves are not random at all and are the same everyone else has to work with. In fact your chances of meeting an aircraft head on at a random point of 55N30W - while small - are much greater than on a truly random great circle route. All traffic flying within 30 miles of you will be funneled to that point.

[complexintentions]

On any given route the only identical track with opposing traffic is the centreline, all the other options utilizing SLOP are offset from each other. So mathematically speaking if collision avoidance is the goal why would you use the only SLOP option common with opposing traffic?

Having spent much more time on the NAT OTS than I've cared to, yes, I'm quite aware they are unidirectional. Just as I'm sure you're aware most of the world is not the NAT OTS. You also might be aware that SLOP was originally implemented because of fears the extremely accurate navigation capability of GPS also increased the risk of opposite direction traffic collisions since everybody was bang on centreline for the first time in history. Wake turbulence of course was a factor as well, but if it was the only one they would have permitted SLOP right or left to give the most options for avoidance from same direction traffic.

My post was only to point out the obvious flaw in your mathematical logic for collision avoidance. For opposite traffic using SLOP there are a total of 5 possible tracks the airplanes could be on, but only one of them is common for both - the centreline. If I'm going to use SLOP that's the one I'm not going to be on unless I need it for wake avoidance.

There is no flaw in the mathematical logic of randomly using all three options on a one-way track system. And it's not my logic.

Rockie, if you aren't going to bother to actually read what others have written, don't post. Please! Either you just don't read or your comprehension is about the level of a child. The comments had clearly narrowed to NATS OTS SLOP, given that, let's see, ahramin posted ICAO Doc 4444, I posted both a link, and a quote from NAT Doc 007, and "NATS OTS" is only written a dozen times. You pompously tell us you've "spent much more time on the NAT OTS than you've cared to" (OOOOOooooh!), but you're the one who posted the question that anyone who really has, would know the answer to. And of course there are other places SLOP is used.

I also already mentioned multiple times that the whole point of it is mathematical randomization due to increased navigation accuracy. Thanks for the sermon ahramin, already covered earlier.

- NATS SLOP is actually centreline, 1 mile, or 2 mile right. The idea is that everyone is doing something random and thus, centreline is also an option. It's all about creating more mathematical randomization. (Comforting, no?)

So yeah, I might "also be aware". This place is like an echo chamber sometimes.

I give up on this one. I point out a simple erroneous statement about a specific operation, post the actual document and the relevant excerpt, but now apparently the discussion was really "well there's other airspace and it's not all NATS OTS and really I was talking about bidirectional routes and" blah blah blah. Chickenshit back-pedalling to hide a minor misunderstanding lol.

Hey do whatever you want folks, makes no difference to me. Run and hide from the scary A380, make up your own procedures, who cares.

[Rockie]

Testy

[xsbank]

One of the difficulties of operating a business jet is that the owners rarely listen to the recommendations of us crew. Hardly anybody is ever strapped in, even during takeoff or landings. The owners are type of personality that doesn't take direction. Besides, how do you handle someone who is tucked up in bed?

I remember one flight to Nairobi in a 605, the family was going on a safari and there were 4 little girls playing dolls on the floor throughout the entire approach and landing. There is only so much you can do...

Amazing that the 604 here was written off for structural damage. Holy crap.

It used to be very common to pull the breaker on the ADG as there was a time when they would deploy capriciously. The racket and vibration they make penetrates your brain even with headsets and to contemplate a crossing with the little bugger deployed is horrifying.

All the controls on the 604 are hydraulic so you would be relying on residual pressure or a windmilling engine to operate them. The ADG runs a generator that runs an AC powered hydraulic pump but even with that working its only part hydraulics (that was tough to remember. I might have to dig out my books...)

I can image the injuries would be people banging about in the back like peas in a colander.

[rxl]

The ADG powers hydraulic pump 3B which pressurizes system 3. With system 3 pressurized, you will have full 3 axis flight control.
Fear of waking the Boss is not a valid reason to disable a critical safety feature.

[Jet Jockey]

Until I hear more info from reliable sources like this one from Bombardier (an advisory wire on the incident) my suspicions about the whole incident were correct...

There was no "dual engine failure", so no RAT deployment and no loss of hydraulic power which explains why they managed to recover from the roll upset.

Also, the aircraft is still parked in a remote area of the airport according to someone that as seen it and he says that externally you cannot see any damages to the aircraft.

Bombardier's advisory wire...

Bombardier issued the following Advisory wire this afternoon concerning this incident...

"This Advisory Wire (AW) is to provide clarification on recent media reporting of a temporary loss of control
event which occurred on a Challenger 604 on January 7th, 2017.

DESCRIPTION:
It was reported to Bombardier that a Challenger 604 was flying over the Arabian Sea at 34,000 feet when it
experienced a temporary loss of control which resulted in significant loss of altitude, abnormal flight attitudes,
and accelerations beyond the certificated flight envelope.
Shortly after the event, the crew shut down one engine due to a high ITT (Inter Turbine Temperature)
indication; the other engine remained operational. The crew eventually regained control of the aircraft, later on
relit the engine which had been shut down, diverted from their intended destination and landed safely without
further incident. There were serious injuries to some passengers on-board. The flight crew reported that shortly
before the event an oncoming large transport category aircraft passed them with 1,000 feet clearance above,
and slightly offset to the left.

The German Federal Bureau of Aircraft Accident Investigation (BFU), representing the State of Registry of the
Challenger 604 involved in this event, has classified the event as an Accident and initiated an investigation
pursuant to ICAO Annex 13 protocols. The Transportation Safety Board of Canada (TSB), representing the
State of Design and Manufacture of the Challenger 604 has been appointed as an Accredited Representative
to the investigation. Bombardier has been appointed as a Technical Advisor to the TSB for the purposes of this
investigation.
Note that Bombardier cannot provide further comment on the investigation beyond what has been stated in this
AW. The BFU, as the investigating agency, will communicate investigation progress as and when it deems fit."

[Benwa]

To put the SLOP issue to rest, In the past Nat doc 007 suggested differently than now. I guess they figured the vast majority of people flying the NAT are equipped.

Nat 007 2013 edition 8.5.3.B

b) Pilots of aircraft capable of programming automatic offsets should preferably not fly the
centre line but rather elect to fly an offset one or two nautical miles to the right of the centre
line in order to obtain lateral spacing from nearby aircraft

[xsbank]

RXL, what I said was that there was a time when the ADGs deployed capriciously so many pilots disabled their ability to deploy automatically because they lost too many flights to inadvertent deployment. Also, the speculation in this case was that two engines quit and the ADG did not deploy (who said the pilots disabled it?) and so directional control would have been possible only until the engines spooled down.

Even with the breaker pulled on the ADG there is a simple manual deploy procedure available to the pilots.

One of the test flight procedures was to deploy the ADG, which we usually did when intercepting the glideslope. The racket is like standing next to a running AC690 on the ground, plus you get the vibration which puts your feet to sleep. It's definitely good news/bad news when it pops out.

Once the company changed the device to deploy with a solenoid not a squib, the capricious deployments became rarer, also there were some electrical issues that were cleaned up so throwing a switch or turning on a service wouldn't cause it to deploy.

It's also why you pin the ADG on the ground lest it pop out (its heavy!) and injure someone doing the walk around while somebody else in the cockpit is powering up.

[Jet Jockey]

We have been operating Challengers since the beginning... we have had in the past some 601 1As, 3As and 3Rs and several 604s and NEVER have we had any ADG issues and never were the C/Bs for the auto deploy system ever pulled.

My guess is that either maintenance or the pilots were not doing something correctly to cause an ADG problem.

[xsbank]

Well I worked for Bombardier and I have spoken to many operators but I only flew 604s, 605s, 300s and Globals. Believe what you wish.

[rxl]

RXL, what I said was that there was a time when the ADGs deployed capriciously so many pilots disabled their ability to deploy automatically because they lost too many flights to inadvertent deployment. Also, the speculation in this case was that two engines quit and the ADG did not deploy (who said the pilots disabled it?) and so directional control would have been possible only until the engines spooled down.

My concern about this resulted from an earlier post which stated that some Challenger operators were in the habit of disabling the auto deploy feature of the ADG.

I have never flown a Challenger (I'm still hoping), but I have flown CRJ 100/200 and 900 (705) at Jazz for almost 15 years and about 8,000 hours worth. I did my initial training at Bombardier with their instructors, one of whom told us that CRJ 100/200 systems are nearly identical to the Challenger 604. I think I know the airplane fairly well but I'm still learning. At one time Jazz operated around 60 CRJ 100's and 200's in high utilization airline service, so likely in the neighbourhood of 1,500,000 hours total and there has never once been a "capricious" ADG auto deploy that I am aware of. Based on that, I would have to say that whatever bugs that existed in the auto deploy system early on have been worked out. Hopefully no one continues to pull that breaker.

[Gannet167]

A frequent question at Flight Safety's recurrent on the 601 was if operators pull the ADG breaker. Apparently, some used to because the older design squip could deploy the ADG for no reason. If memory serves right, the max continuous IAS on the ADG is 200 kts and I believe there's an altitude restriction as well. Having that thing pop at 30 west, at altitude would make for a very bad day - and not merely because of the extreme noise and vibration. I guess they thought there's always the manual deploy handle in the unlikely event you need it. However, with the newer designed components installed, I think the same parts as the 604 and RJs, there were no inadvertent deployments and no reason to pull the breaker. I think Flight Safety wanted to ensure everyone knew there was no longer any reason to consider pulling the breaker as everyone had the mod.

[xsbank]

Interesting but I remember it as not being a problem with the squib but an electrical glitch, a spike or similar, that fooled the ADG into thinking the a/c had lost power. That's why you pinned it on the ground because turning the power off and on might cause it to deploy and hit someone.

And yes, there are definite limits to its use, you wouldn't want it to come apart and hit some of the expensive stuff on that side of the a/c.