RW Flight Planning - From The Horses Mouth

[RickB1293 9]

I posted this here because I do most of my flying in the T7 and the topic is relevant to long distance flight planning like that used with the T7. If this is the wrong area please excuse me.

 

I had an interesting opportunity to discuss our hobby with one of my hockey team dads. He's a captain and IP for Sun Country (SCX) and flies the 737NG-800. In addition to their vacation routes SCX also flies charter hops for the military. They fly mostly US to Germany with stops at Gander and Shannon for fuel given the NGs operating range. All of their aircraft and crews are ETOPS 180 certified as needed to fly the transatlantic routes.

 

We had a very detailed conversation about route planning and dispatch. What surprised me the most is that they almost always fly point to point instead of following J airways. On transatlantic hops they do fly NATrack when conditions dictate and fly direct from departure to the track entry point. This is indicated on their filed flight plan and the flight is followed by appropriate ATC upon clearing the TCA or at the end of a SID if required. STARS (rarely) and Approaches are assigned by the destination ATC. If they are assigned to an airway they request a two mile offset to increase separation from other aircraft flying the same route and to minimize possibly encountering wake turbulence. This is requested by each crew based on the pilot's judgement but is considered SOP for the airline. 

 

I've been using PFPX for almost a year and have never seen a direct route produced by the program. Sun Country's study showed a nearly 1% savings in fuel cost and shorter "time between" by this routing. I was wondering if anyone has experience with this and if other airlines do the same thing. SunCountry flies between dozens of North American cities, Mexico and to many Caribean islands and the "direct to" routing is almost exclusively used.

 

BTW, my new buddy also gets to fly right seat in our CAF B-25, lucky buck. He also invited me to share some time in SCX's Level D 737-800 simulator during the two weeks he usually has off between flying. I hesitantly accepted.

[777simmer 117]

Flight planning is actually more a dispatchers specialty....maybe there is one around here?

 

But my experience is that the USA especially is quite flexible when it come to direct routes.

I dont know about short range flight in the USA (I often hear them read back whole ATC route (re)clearance to clearance delivery with a bunch of airways) but going long haul from JFK to Europe we would usually get something like:

Kennedy1 departure PUT transition direct EBONY N303A RIKAL then NAT track....

 

In Europe/Asia/Russia/Middle east you file airways and you fly them.

In Europe you can expect in flight ATC "directs" but they are less common in Asia and Middle east.

 

Our dispatchers file as from A to B along the cheapest route ofcourse.

 

But for the OFP fuel planning they are conservative.

Using the expected t.o and landing rwy and the FULL SID and STAR!

And no shortcuts in flight either.

This way you have enough fuel to complete the flight even if you dont get any short cuts and even if you have to fly one of those complete S-turn STARs

So the OFP is usually quite a few miles longer then the real flight!

[RickB1293 9]

Thanks Rob, that makes sense. SCX files mostly US and Caribean routes except for their charter contract which is shared with Delta. I'll ask my buddy about their Europe practices but he's already said that they are a lot tighter re airspace mgmt.

[scandinavian13 5,192]

As mentioned, flight planning in the airline environment is a dispatcher specialty (so, the horse would be the dispatcher, not the pilot). I'm going to give this guy the benefit of the doubt and say he just didn't explain this as clearly as he should've.

 

I'll explain:

 

The knowledge below comes from working on the FAA CDM initiative, which is an initiative between the FAA and operators to better utilize and develop the National Airspace System (NAS). In other words, I sat next to routing (both operator and ATC) subject matter experts for an entire year.

 

 

 

We had a very detailed conversation about route planning and dispatch. What surprised me the most is that they almost always fly point to point instead of following J airways. On transatlantic hops they do fly NATrack when conditions dictate and fly direct from departure to the track entry point. This is indicated on their filed flight plan and the flight is followed by appropriate ATC upon clearing the TCA or at the end of a SID if required. 

 

When you look at the flying that they usually do, the point to point stuff starts to make a little more sense. If you look at a site like Skyvector, you'll see that there really aren't a whole bunch of J airways in the directions they're going. Most of the J airways in the area south of them are east-west, which does them little good. The midwest ARTCCs ("Centers") tend to be a little more flexible with how they accept routing for this reason.

 

As far as the NATs go, if you're flying anywhere near the NATs, you're going to be flying a NAT. Flying below the NATs would allow you to fly your own route, but it also limits you to altitudes where you wouldn't be able to get across in a 737 - flying above them isn't possible in the 737. Heck, part of the reason they have what seems like an agreement with ZNY or ZBW (NY and Boston ARTCC, respectively) is likely because it'll help them get across the Ocean without brushing up against reserves. I don't know their numbers, though, so I can't say for sure.

 

 

 

STARS (rarely) and Approaches are assigned by the destination ATC. If they are assigned to an airway they request a two mile offset to increase separation from other aircraft flying the same route and to minimize possibly encountering wake turbulence. This is requested by each crew based on the pilot's judgement but is considered SOP for the airline. 

 

For every flight I can see of theirs today, they're all assigned STARs. The "assignment by destination ATC" thing is a European thing (for the most part). I think he probably just didn't convey that very well to you. If you're going into NY, you're getting a STAR, and likely a J airway to get to the transition. You can always not file a STAR and add a NO SID/STAR remark, but that's puts the flight at the whim of controller vectoring and sectorization. Even though you don't file it, the controller will likely vector you in via the same path anyway so that you are "part of the stream."

 

The offset thing is more of a NAT procedure, though it could be used on airways. Airways are 8nm wide (it's slightly more complex than that, but that's a different discussion), so you can potentially use up to 4nm on each side.  Still, I doubt that it's used in the Contiguous US as much as on the NATs, even for them.

 

Either way, the wake turbulence thing doesn't make much sense to me at all. The min separation between aircraft at the center level is 5nm (again, more complex than that, but keeping things basic here), which all but covers a 737 following any aircraft except the A380 (and even then, you're not usually going to be at min sep anyway, unless you're flying into a crazy busy field). On the NATs, this is eradicated entirely, as the separation mins there are 30+ nm (I forget the exact time-based metric), so wake turbulence really doesn't come into play.

 

 

 

I've been using PFPX for almost a year and have never seen a direct route produced by the program. Sun Country's study showed a nearly 1% savings in fuel cost and shorter "time between" by this routing. I was wondering if anyone has experience with this and if other airlines do the same thing. SunCountry flies between dozens of North American cities, Mexico and to many Caribean islands and the "direct to" routing is almost exclusively used.

 

PFPX is a very powerful tool, and one that I don't think people give enough credit. There are heaps and heaps of options that people simply overlook (one of them, if I recall correctly, relates to how strictly it will follow airways).

 

Moreover, remember that it's a routing tool. It's made to route you via known routing. It wouldn't be very good if it were programmed to just free-form its routes, disregarding airways. Directs in the SCX plans are the dispatchers likely overriding whatever program they're using, and manually setting certain parts of the route.

 

To be a little more precise, too, it's not direct from departure to destination. It's direct between certain major points, like this SCX flight plan for MSP-MCO: RST7 ALO ENL BNA WALET OTK PIGLT4.

 

 

 

Always be careful with aviation info. The problem with our industry is that information is usually pretty niche, full of technicalities, and reasonably hard to come by. Moreover, people in the industry are usually pretty specialized. Controllers, dispatchers, pilots, rampies, and all the rest usually have their own specific realm of knowledge, with usually only a cursory understanding of the rest. A pilot may well be very knowledgeable, but it doesn't mean he or she is a subject matter expert on all topics aviation, to include routing and the technicalities thereof. I'm sure you know this, but the way the post is titled with "from the horses mouth" kinda illustrates my point in that it's assumed that a pilot is an authoritative source, which I have doubts about. A pilot may know a lot, but the best source for this kind of information would be a dispatcher.

[redwood320 0]

Actually the 2 mile offset on the NAT tracks makes a lot of sense. Typical wake vortices will descend, and spread. With 1000' vertical separation and the thundering herd of the various Boeings, Airbi, and even 757s in the mix, can make for a sometimes eventful ride. Watching the autopilot struggle against the roll rate of a 757 wake is not much fun to watch....

[SimBrief 25]

I'm sure you know this, but the way the post is titled with "from the horses mouth" kinda illustrates my point in that it's assumed that a pilot is an authoritative source, which I have doubts about. A pilot may know a lot, but the best source for this kind of information would be a dispatcher.

 

Agreed. I would however give the edge to the pilots when it comes to wake turbulence issues. 5 mile in-trail on an airway might be ok if both aircraft are at the same altitude (the wake should descend before the second aircraft gets there), but if I was following another aircraft by even as much as 30 miles and 1000ft below their altitude, you can be sure I'd be considering my options. If there was a strong crosswind that I knew would blow the wake off to the side I might be ok with it. Otherwise, I might request an offset/direct/heading to get out of the way. Just in case.

 

That being said, I can't say I've ever heard SCX routinely requesting offsets along airways, though I don't fly in the same areas as them all that often. That would seem quite unusual to me, normally that kind of request is only made if you know of another aircraft in your vicinity that could be an issue (this is relatively rare though). Or for other obvious reasons like weather, it's a question of airmanship really.

 

 

 

Actually the 2 mile offset on the NAT tracks makes a lot of sense. Typical wake vortices will descend, and spread. With 1000' vertical separation and the thundering herd of the various Boeings, Airbi, and even 757s in the mix, can make for a sometimes eventful ride. Watching the autopilot struggle against the roll rate of a 757 wake is not much fun to watch....

 

Also agreed, but I don't think Kyle was disagreeing with that. In any case, offsetting along the NATs is SOP these days (see "SLOP"). Both for extra spacing and wake avoidance. Certainly the 757 is one you'd want to avoid though, those wakes can be nasty.

[RickB1293 9]

Don't blame my buddy for any technical lapse or misstatement. That fault is entirely mine. I started this topic to engage others that have real knowledge about systems and procedures that we amateurs don't have enough sense to talk intelligently about. I compare it to a doctor "dumbing down" his diagnosis so that his patient can understand him. If my buddy knew that his examples were going to be filtered through the prism of an ignorant fool, he would have used small words and big crayons to explain things. . .

 

 

 

Kyle was right about the STARS, our conversation was about their use of the NG-800 across the pond and their ETOPS capabilities. Again I wasn't as clear as I should have been, he was talking about European Airspace and the trip over to their charter destinations. I'm not sure they use the SCX callsign in their charter capacity I frankly wasn't looking at that much detail. As far as the direct routing, SCX is based at KMSP and many of their routes either begin or end here. He's going to get some copies of their actual flight plans so I can compare them to what I get from PFPX. I'll be glad to share them if it's okay with him.

 

Regarding their use of offsets our discussion was about NextGen (https://www.faa.gov/nextgen/) and the reduction in separation the system will deliver. That led into SCX's use of airway offsets as a means to provide cautious avoidance of other aircraft through lateral and vertical separation. The problem of wake turbulence was merely an example and I didn't take it to be the sole reason for the procedure. I can say that my impression, though an amateur's, is that they are definitely a belt and suspenders organization and they place a lot of emphasis on flight safety, crew training and passenger comfort i.e. satisfaction.

 

Actually I think it's good to pick apart threads like these. The whole point of this topic was to solicit the experience of other more knowledgeable followers who are able to shed light on arcane subject matter. In the real world I'm a testifying expert witness in the state and federal court systems. My area of expertise is in short range transportation control forensics - meaning elevators, escalators and any other conveyance that moves people or things within a building.

 

In the courtroom I have to filter down incredibly technical subjects, laced in nuance and described in jargon that absolutely befuddles the panel of six to twelve laypersons who don't have a clue about the facts of the case. We talk about proximate cause, reasonable expectations, standard of care and common law.  If I oversimplify I get hammered by opposing counsel for "talking down" to the jury. If I get too technical, their eyes kind of glaze over and I've lost them. That sometimes happens in these forums. So please, just remember that no one reading this is ever going to go out and jump in an airplane and fly based solely on what they learn here. Regardless of the guy who swears he learned to fly from a desktop to FSX, it just ain't gonna happen (thank God).

[scandinavian13 5,192]

Actually the 2 mile offset on the NAT tracks makes a lot of sense. Typical wake vortices will descend, and spread. With 1000' vertical separation and the thundering herd of the various Boeings, Airbi, and even 757s in the mix, can make for a sometimes eventful ride. Watching the autopilot struggle against the roll rate of a 757 wake is not much fun to watch....

 

SLOP on the NATs makes sense. I wasn't questioning it at all. Regardless, wakes do dissipate.

 

 

 

I would however give the edge to the pilots when it comes to wake turbulence issues. 5 mile in-trail on an airway might be ok if both aircraft are at the same altitude (the wake should descend before the second aircraft gets there), but if I was following another aircraft by even as much as 30 miles and 1000ft below their altitude, you can be sure I'd be considering my options. If there was a strong crosswind that I knew would blow the wake off to the side I might be ok with it. Otherwise, I might request an offset/direct/heading to get out of the way. Just in case.

 

I take it that you don't fly for the airlines. Wakes dissipate with time. The stated lateral wake turbulence mins per the wake recat are more than enough, regardless of altitude. Sure, you're right that they descend, but at 30 nm they're all but gone, regardless of altitude.

 

I definitely agree that I'd defer to the decision-making of the pilot if he or she felt threatened, but if more than the stated wake sep mins were required, then we'd all be screwed in the United States. Just for reference, we routinely run 5-15 MIT into NY from Washington Center (and 5 MIT is a lateral metric only - the aircraft are routinely not at the same altitude).

 

As far as the 757 comment goes, the recat study actually found that the 757 effects were somewhat overstated. While it still has special class because it still has more of an effect than other Larges, the separation was reduced for the most part.

 

 

 

He's going to get some copies of their actual flight plans so I can compare them to what I get from PFPX.

 

For what it's worth, look at FlightAware. What is shown on that site is what they end up flying as it's pulled directly from the FAA systems (when Stateside - it even shows any controller modifications to the route). The paperwork might show you what they originally filed, or what they used to plan the fuel, but it's only a snapshot of their intention, and not necessarily what ATC gave them, or what they flew.

 

 

 

Regarding their use of offsets our discussion was about NextGen (https://www.faa.gov/nextgen/) and the reduction in separation the system will deliver. That led into SCX's use of airway offsets as a means to provide cautious avoidance of other aircraft through lateral and vertical separation. The problem of wake turbulence was merely an example and I didn't take it to be the sole reason for the procedure. I can say that my impression, though an amateur's, is that they are definitely a belt and suspenders organization and they place a lot of emphasis on flight safety, crew training and passenger comfort i.e. satisfaction.

 

Not sure if I agree with this, though I'm welcome to being corrected (on their use of offsets, at least). NextGen would actually increase separation by reducing the margin of error in actual track versus assumed track. The increase in precision issue that lead to the use of SLOP on the NATs is an entirely separate issue (increased precision, but lack of radar coverage to ensure separation).

 

 

 

So please, just remember that no one reading this is ever going to go out and jump in an airplane and fly based solely on what they learn here. Regardless of the guy who swears he learned to fly from a desktop to FSX, it just ain't gonna happen (thank God).

 

You'd be surprised. A lot of the bad information that I see here or in other aviation forums has occasionally been heard at my local airport.

[RickB1293 9]

Wow Kyle, now that's scary! You've brought up good points. I'm sure that Todd and I will have some good points to discuss. I'll get back to you all with their rational regarding offsets the other separation issues. You guys have made for some interesting reading, thanks.

 

Rick

[scandinavian13 5,192]

Wow Kyle, now that's scary! You've brought up good points. I'm sure that Todd and I will have some good points to discuss. I'll get back to you all with their rational regarding offsets the other separation issues. You guys have made for some interesting reading, thanks.

 

Rick

Thanks for bringing the topic up. Best discussions are the ones that bring different views in and challenge viewpoints.

 

It is kinda scary what I hear out there, honestly.

[RickB1293 9]

We need Driver's Ed for airplanes. Commercial pilots don't enough credit, the volume of informantion on so many subjects. It's not just aviate, navigate, communicate for them. I don't see how they keep up with all the changes. I appreciate the time that real aviation people share on the forums. Look at products like PMDG, ASN, PFPX and the EFB stuff you realize that flight simming is a pretty small and amazingly technical niche market. I don't know if it's the allure of mastering something that is so technically challenging or the love of flying that draws me. I have always been the guy that takes something apart just to see how it works I guess, drives the wife nuts cause I can't seem to leave sleeping dogs lay.

[SimBrief 25]

I take it that you don't fly for the airlines. Wakes dissipate with time. The stated lateral wake turbulence mins per the wake recat are more than enough, regardless of altitude. Sure, you're right that they descend, but at 30 nm they're all but gone, regardless of altitude.

 

Ouff that felt slightly dismissive haha . Without going into detail, I do fly for the airlines. I regularly go into the busy east coast airports.

 

Admittedly it's tough to convey my intent through a forum post, when it comes to this stuff it's always going to be a judgement call. Every situation will be different.

 

Let me start off by saying that 30nm was a bit much, allow me to retract that. I re-read my post afterwards but couldn't edit it anymore. If I had to ballpark it, I'd say anything within 10 or 15 miles would probably get my attention (that is to say, it would prompt me to evaluate the situation. Not an automatic deviation). And just to clarify, I'm talking about wake avoidance during the cruise portion, that is at high altitudes where the flight envelope is significantly more narrow. Moreover, there is a distinction to be made between simply crossing paths with traffic, and flying parallel along the same track as traffic. More on that below.

 

On descent or approach is a different situation in my opinion, and I'm comfortable with the current separations being applied in those phases. Even if you were to encounter wake on descent, the separation and airspace structure is such that any encounter is likely to be short lived. And depending where you are, you probably already have the belts on and/or the cabin is mostly secure or in the process of being secured.

 

I consider cruise differently because of the narrow envelope, the fact that it's generally otherwise smooth and the belts aren't on, you're flying much faster (applying the same spacing at higher speeds means you will reach the wake quicker and it won't have dissipated as much), and you have FAs in the back serving drinks/coffee/food. Obviously, when evaluating the situation you consider all the factors available to you. For example, I'd be much more likely to deviate if I saw the vapor trail (generally a good indication of where the wake is) is moving to intercept us, or if I don't see a vapor trail at all and I feel there is a chance the wake will end up in our vicinity.

 

(Disclaimer: the use of the word "I" is only because I'm talking about my own views on the subject. Obviously in the cockpit you would discuss the situation and come to a decision as a team).

 

One situation I've seen was crossing 1000ft below another aircraft on the same airway going in the opposite direction. The resulting wake, should we have encountered it, would have been parallel along our track and would have resulted in a prolonged encounter if we flew lengthwise through it. How bad would it have been? I have no idea, but that wasn't the time nor the place to find out. In the past year I've actually requested a deviation for this only once, so it's quite rare. There have been 1 or 2 other similar situations but the crosswinds and visible vapor trail were such that we deemed it not necessary.

 

I recognize that a lot of study goes into defining the minimum wake separations, and as a pilot I recognize that the system wouldn't work if every pilot and his dog requested special treatment in excess of the minimums. My only argument is that these minimums are a "risk mitigation" tool and not a guarantee that the following aircraft won't encounter wake. Every airline pilot has encountered wake outside of the prescribed minimum separations, conditions and circumstances are such that it happens sometimes. Bottom line: As pilots, our #1 priority is always the safety of the flight, and any pilot who feels a situation is unsafe has a responsibility to do something about it, regardless if it's convenient for ATC or not. I know you weren't disagreeing with that or anything, I just wanted to restate it.

 

Moving on, you could be right about the 757 wake, my comment was merely based on the years of cockpit gossip and not on any formal studies I've read. If you have a link to a 757 wake study or something like that I'd appreciate it, thanks!

 

 

You guys have made for some interesting reading, thanks.

 

Thanks for bringing the topic up. Best discussions are the ones that bring different views in and challenge viewpoints.

 

Agreed, it's good to have discussions like this, so thanks for posting, Rick! I'm not convinced (yet) that my viewpoint is all that different from Kyle's, but we'll know more once he responds to this post. :ph34r:

[scandinavian13 5,192]

 

 

I recognize that a lot of study goes into defining the minimum wake separations, and as a pilot I recognize that the system wouldn't work if every pilot and his dog requested special treatment in excess of the minimums. My only argument is that these minimums are a "risk mitigation" tool and not a guarantee that the following aircraft won't encounter wake. Every airline pilot has encountered wake outside of the prescribed minimum separations, conditions and circumstances are such that it happens sometimes. Bottom line: As pilots, our #1 priority is always the safety of the flight, and any pilot who feels a situation is unsafe has a responsibility to do something about it, regardless if it's convenient for ATC or not. I know you weren't disagreeing with that or anything, I just wanted to restate it.

 

I'm only quoting this one part of the post for the sake of space, but I'll touch on various parts. While I do somewhat apologize for the dismissive tone, I think we both agree that it stemmed from the 30 MIT statement which was rather extreme. My guard is always up because in sim forums there are a lot of members who are vague on the details of their experience and like to throw their opinions into the mix as if they have experience that gives their opinions weight. Since it wasn't clear, I challenged it a bit.

 

I've been following that you've been referring to cruise, which is where the ZDC -> ZNY comment came in (that sequencing happens at cruise by ZDC, though I didn't go a good job of clarifying that).

 

You're right that the mins are not guarantees, but one must also keep in mind that physics prevail here. It's not like physics jump in and immediately follow our rules on paper, but given the intense amounts of studies we've given them recently, the metrics have reasons behind them. Even if you do end up catching some of the effects at the mins, they'll be very weak at that point. Since air is tough to see, think of the wake of a ship (remembering, as well, that aero and ocean engineering are often taught as a single program in universities because air follows fluid dynamics). The wake is the worst immediately behind the ship, while it tapers off the farther back you go. Even though the cavitation (air bubbles) is still visible for miles, the effects to other vessels are essentially negligible. In the air, wakes do not retain strength and then suddenly dissipate, though it seems that many pilots think this for some reason.

 

I fully agree that the pilot should act in a manner that ensures the flight remains safe, but a pilot's judgment is limited by his or her knowledge. The knowledge of wake turbulence that's out there in the pilot group is generally pretty cursory, and heavily saturated with the bias of whoever is teaching the topic at that moment (this comment is anecdotal, based on discussions I've had with other pilots about it). Erring on the side of caution is understandable, but people often blindly follow this safety first 'rule' without actually using their own brains to weigh the risks (more common in this industry than one would think). I'm not accusing you of this, but I do know that many of the operations I've worked for simply stated what is safe and what is unsafe in black and white terms without giving reasons for people to make more educated decisions in the moment. Over time, that lead to people not being to exhibit any decision-making at all, simply following the 'safety' mindset blindly.

 

Example:

One ground operator told its employees that a belt loader was never to be used in place of stairs because it is "unsafe."

"Believe us. It's unsafe. Why? Because we say so. Never use it for anything other than loading bags. Ever."

Never mind the fact that a ramp tends to be a lot less of a slip/trip hazard than stairs, adding to this that the belt is usually a non-slip, rubberized surface. Heck, the only reason we use stairs in building is that they take up a heck of a lot less space than ramps do. An example of unauthorized use one time was a rampie using the belt loader to connect the HP air on the CRJ 700. No...use a ladder instead, because it's made for climbing.  :mellow:

 

Adding to this, the outfit stated that the air start unit should be powered and running at idle during this process, so they were essentially asking you to climb, one-handed, up a ladder with a pressurized hose to plug it in (usually a two-handed job) in the interest of "safety."

 

Sorry for the rant, but I believe that in not providing people with all of the evidence to make the right decisions actually decreases safety instead of increasing it in the end. Not stating reasons, or not providing evidence or backstory usually simply perpetuates false information floating around.

 

 

 

Moving on, you could be right about the 757 wake, my comment was merely based on the years of cockpit gossip and not on any formal studies I've read. If you have a link to a 757 wake study or something like that I'd appreciate it, thanks!

 

My info on this is actually slightly behind (timeline-wise). Despite doing some of the ground work for the recat, my time on that contract ended a couple years ago, so I didn't see that they fully converted in June and the 757 category has been fully dropped. The cockpit gossip really stemmed from a lack of study, anecdotal testimony, poor selection of the weight classes in the past (completely ignoring aerodynamics, and other factors - see the Volpe link below), and a lack of technology to study it.

 

You can actually see the "mixed" state in this AC from the FAA earlier this year:

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_90-23G.pdf

 

...and the final language here (the table is on A12):

http://www.faa.gov/documentLibrary/media/Order/7110.659A.pdf

 

The changes are highlighted here on page two (shows where distances were mostly decreased - blue - but also increased - green, for the smallest cat).

http://www.faa.gov/other_visit/aviation_industry/airline_operators/airline_safety/safo/all_safos/media/2012/SAFO12007.pdf

 

Finally, the group that I worked most closely with was Volpe, whose more info-graphic approach might be a little more interesting to some (though it also includes more background apart from the above links of "this is the rule"):

http://www.volpe.dot.gov/sites/volpe.dot.gov/files/docs/Wake_Turbulence_Infographic_508.pdf

[SimBrief 25]

I've been following that you've been referring to cruise, which is where the ZDC -> ZNY comment came in (that sequencing happens at cruise by ZDC, though I didn't go a good job of clarifying that).

 

Fair enough, I've actually flown that airspace quite often and have never been put in any position I wasn't comfortable with regarding wake turbulence in cruise. The (few) issues I have had are actually in relatively quiet airspace, where there are fewer airways, most of the traffic is flying either east or west, and it's not uncommon to fly behind, beneath, or to cross paths with another aircraft flying the same airway either in the same direction or in the opposite direction as you. In the specific situation I've been referring to where I deviated for wake, we could actually see the wake descending through the vapor trail and it was apparent we were going to fly through it. I don't know how strong it would have been, maybe it would have just cause light chop, but why on earth would I risk flying through it when all I had to do was request a minor course deviation?

 

 

 

You're right that the mins are not guarantees, but one must also keep in mind that physics prevail here. It's not like physics jump in and immediately follow our rules on paper, but given the intense amounts of studies we've given them recently, the metrics have reasons behind them... In the air, wakes do not retain strength and then suddenly dissipate, though it seems that many pilots think this for some reason.

 

Absolutely, I certainly wasn't implying that the wake 5+ miles behind was even close to as strong as it was at the onset. Though it's good that you mention it as I don't think either of us had touched on that yet. I haven't noticed any major misconceptions regarding this amongst my aviation circle, but it's a shame to hear that misconceptions still exist.

 

 

 

Even if you do end up catching some of the effects at the mins, they'll be very weak at that point.

 

Sure, most of the time. Generally, if you do hit anything, you will at most get a few ripples, possibly a very brief jolt if you're unlucky and hit the worst of it. For this reason, the spacing policies work and the research has certainly increased safety, I'm not questioning that.

 

On the other hand, I was once #2 on approach, 5 miles behind an Embraer (of all things) and with no warning the aircraft banked to about 60 degrees before I even had a chance to turn off the autopilot and bring it back manually. My aircraft was a Cat E, following another Cat E according to the 3rd link you posted above, with more than the recommended amount of space. These situations are obviously incredibly rare, but they do happen. And if they happen on approach when the seat belts are on and everyone's seated, fine. But I sure don't want that happening at FL400, with people walking around the cabin, with 20 knots between my upper and lower airspeed limits. It's not something to be paranoid about, it's just something that I feel should be taken more seriously than your tone would suggest. It isn't about blindly following the "safety first" culture without thinking for oneself, it's about the difference between being 90% sure nothing will happen, and being 100% sure nothing will happen. Not ranting or anything by the way, just furthering the conversation.

 

You seem to have some knowledge regarding in-trail spacing at the higher levels, I'd be interested to know more on what kind of criteria the FAA uses when spacing aircraft at high levels. Do they vary spacing based on weight categories like they do on approach? You quoted 5-15 miles in a prior post, but that's a fairly wide range. I'm more familiar with the Canadian regs so I'd be interested to hear the FAA side of things.

 

The reason I ask is because surely they can't apply the same minimums at altitude as they do on approach. Even at 2.5nm spacing on an approach, and considering above average approach speeds, that leaves at least 1 minute for the wake to dissipate before the next aircraft passes. Conversely, 5nm spacing at altitude when dealing with 500kts of groundspeed would give little more than 30 seconds, hence my curiosity. While it's practical to space aircraft by reference to in-trail distances, I think we can both agree that what really matters is the time delay between passage.

 

I guess all I'm really trying to add to this conversation is that as someone who has dealt with wake turbulence in a practical context, respecting the minimum separation is a great policy, but one should not take it as a guarantee that you won't get surprised one day.

 

EDIT: Thanks for the links by the way, I appreciate it!

[scandinavian13 5,192]

 

 

I don't know how strong it would have been, maybe it would have just cause light chop, but why on earth would I risk flying through it when all I had to do was request a minor course deviation?

 

haha - you know that if passengers had any say they'd blame the chop solely on you anyway...

 

 

 

On the other hand, I was once #2 on approach, 5 miles behind an Embraer (of all things) and with no warning the aircraft banked to about 60 degrees before I even had a chance to turn off the autopilot and bring it back manually.

 

I highly doubt it was 60 degrees, or it wasn't the Embraer that caused it, honestly. Aircraft of similar categories like that shouldn't exhibit those effects. Even 20 degrees would be extreme within the same class. I'm guessing there was more at play here. The fact that we (during the recat study) found that MRS would be okay between similar classes means that there was significant evidence that aircraft within the same category would be nearly unaffected.

 

 

 

You seem to have some knowledge regarding in-trail spacing at the higher levels, I'd be interested to know more on what kind of criteria the FAA uses when spacing aircraft at high levels. Do they vary spacing based on weight categories like they do on approach? You quoted 5-15 miles in a prior post, but that's a fairly wide range. I'm more familiar with the Canadian regs so I'd be interested to hear the FAA side of things.

 

Spacing is usually much higher than minimum simply because of the way traffic works out. If it gets set to a specific level, it's usually 10-20 MIT because multiple streams must be converged into only a few/couple/one (depending on the field/runway layout). One of the links I posted earlier actually differentiates between approach and en route for wake distance, though I forget which one at the moment. The 5-15 was more related to my earlier mention of traffic management restrictions rather than wake separation. The bare minimum is the maximum of wake and radar separation requirements.

 

At the center level, the basic requirement is 5 nm and 1000 feet, but wake sep can mean that this is increased slightly (up to 7 nm). No adjustments are made for speed, somewhat under the assumption that the min sep (wake or radar) is sufficient, or the pilot will speak up if necessary. Above 7, that's all restrictions placed on ATC by other facilities. As an example, during heavy traffic periods, ZNY may place a 20 MIT restriction on arrivals from ZDC into Airport X (usually LGA - single runway there - but it could also be EWR or JFK). That's a separate beast, but that's why I used the 5-15 metric (just an average, really).

 

 

 

The reason I ask is because surely they can't apply the same minimums at altitude as they do on approach. Even at 2.5nm spacing on an approach, and considering above average approach speeds, that leaves at least 1 minute for the wake to dissipate before the next aircraft passes. Conversely, 5nm spacing at altitude when dealing with 500kts of groundspeed would give little more than 30 seconds, hence my curiosity. While it's practical to space aircraft by reference to in-trail distances, I think we can both agree that what really matters is the time delay between passage.

 

Agreed, but remember that in the terminal environment two things are in effect here: aircraft are descending, and wakes descent. So, even if you were at MRS, the following aircraft is usually above the leader in altitude, and the wake of the leader is descending even further below the lead itself. So, time delay + altitude are the major factors, though there are several minor factors.

 

 

 

I guess all I'm really trying to add to this conversation is that as someone who has dealt with wake turbulence in a practical context, respecting the minimum separation is a great policy, but one should not take it as a guarantee that you won't get surprised one day.

 
EDIT: Thanks for the links by the way, I appreciate it!

 

Absolutely. I've seen a whole bunch of evidence in my time working on the NextGen concepts that wake is all but fully attenuated at the mins, but outliers exist.

 

You're welcome - I'm an evidence nerd myself, so I fully understand the want for official "evidence" if you will.