Roll on Offset Airways Tracking

[OVERTALK]

Collision in air averted
.
By Our Staff Reporter
.
KARACHI, Jan 17: A major air disaster was averted due to timely functioning of an automatic warning system in two passenger planes, which accidentally came face to face at the same altitude over Panjgur in the west of Balochistan.
An Air Blue flight was headed for Islamabad from Dubai. While flying at an altitude of 33,000ft altitude, it came in front of an Eva Airways flight bound for Hong Kong from Europe, on Tuesday morning.Fortunately, the planes escaped a head-on collision as the automatic warning system came into play when the two planes were five nautical miles apart, over Panjgur. Responding to the warning, the Air Blue plane descended while the Eva Air flight took an ascent.
Upon landing in Islamabad, the captain of the Air Blue flight reported the incident to the Civil Aviation Authority (CAA), which launched a probe to ascertain how the planes were flying on the same air route.
According to sources, preliminary findings attributed the matter to the negligence of Air Traffic Control.

[square circuit]

I wish ATC could make more use of offsets.
I occasionaly use them with High level overflights.
Saves using lots of headings and watching that pesky drift!
Technically we should have both Aircraft locked on radar headings when less than 15NM apart.Lateral offsets would let us go down to 5 without any hassle.
Oh well maybe we will catch up with technology sometime!:ok:

[WHBM]

Unlikely to have been a head-on as both aircraft were heading east.

[410]

Offset tracking is already authorised over India and Pakistan, but I've yet to pass ONE SINGLE aircraft using it (apart from me!) since it has been given the official OK, and I never cease to be amazed at the way 99% of my FOs can't wait to get back on the airway centreline the moment we pass out of Indian airspace.

Standing by for the (usual) "it won't save you in all circumstances" posts that always follow when this subject is broached.

[chevvron]

Offset tracking was often used where DECCA navigation was available but there were few VORs, the instruction from ATC being 'fly DECCA left'.

[Green Guard]

:D

I too can not explain, urge to flock in the very center of Airway,
except that many creatures tend to flock tight when in fear...
like sheep when the wolves are near

Wish to know if they drive their cars in the center of the road..
I mean just over the central line or lights ?

:=

[185 Lbs of Ballast!!]

Hi all

I wrote the following letter to Flight International back in 2004 and it was published in the mag:

The Editor
Flight International
Quadrant House
The Quadrant
Sutton
Surrey
SM2 5AS

22 March 2004

Dear Sir

I have decided to put in a letter to you a concern that I have fostered for some time.

I have just finished a 10hr flight back to Europe and have been watching traffic coming in the opposite direction approximately 1nm to my left.

With the advent of such accurate navigation systems I had an ANP of approximately 0.05nm and I suspect the opposite traffic had almost exactly the same performance due to their GPS. I do consider that as an industry we are allowing this superb accuracy to infringe upon our level of safety.

I flew the majority of the way offset to the right of track by 1nm and therefore well within the limits of the airway. Generally, airways traffic ploughs back and forth almost directly above and below each other and very rarely do I observe offset traffic. Personally, I would very much like to see some sort of universal safety advisory recommending that when the crew has the facility to do so, they offset their track. I offset to the right just as one does when following a line feature under VFR.

I do not mean to suggest that aircraft are about to start falling around our ears, however, it does seem a little short-sighted to voluntarily degrade ones margin for error.

With your assistance, it seems that your publication would provide a good forum for some professional discussion of this issue which could perhaps lead to safer skies for us all.

Yours sincerely


It does seem rather silly to ignore the problem, unfortunatly I think it will take a disaster to raise the awarness high enough for it to be taken seriously...:\

[410]

unfortunatly I think it will take a disaster to raise the awarness high enough for it to be taken seriously...The disasters have already happened, out of Delhi in 1996 and a few years later, off the West African coast and last year in Brazil.

400 people died in the Delhi crash, but they weren't from North America, so CNN didn't turn it into the talk fest it would have been had 400 Americans died. Sadly, I think it's going to take a mid air between two wide bodies carrying US or Western European citizens to shake the system up enough to address this problem - a problem, I hasten to say, very few within the Industry think exists.

I'm sure i've already offended some who've misunderstood my comments above, so I'll dig myself an even deeper hole. Would anyone care to comment on the CNN reporting of the Brazilian tragedy had the people and aircraft involved been switched to 100+ US citizens killed in the 737 and two Brazilian pilots in the Embraer?

[FullWings]

It's funny how only recently there has been some movement on this issue: Strategic Lateral Offset Procedure (SLOP :rolleyes: ) on the North Atlantic. OK, good idea but this is last place this is needed considering all the aircraft on the track system have TCAS, are RVSM certified and are monitored closely from both sides of the pond. Much better to implement this enroute everywhere else.

Personally, I have flown offsets for the last 10 years or so, especially when over Africa/Middle East/Far East/South America. I did meet someone over Nigeria who was flying a 2nm left offset in riposte to my 2nm one to the right... luckily not quite at the same level.

410 mentions the 737/Embraer mid-air in Brazil - if either had been flying an offset...:sad:

(When the NA procedure was first brought out, I remember seeing "On OTS consider SLOP" printed on the flight plan. Neither of us had a clue what it meant until we got someone to explain it on 123.45)

[Sky God]

It's been years since I've been asked to fly an Offset track. Thanks for bringing the subject up - time to get my head back in the FMS manual again.

Can't imagine why ATC don't use them more often.

Sky God.

[Tarq57]

Can't imagine why ATC don't use them more often.

All respect, but it's not actually up to ATC to issue/use them.(Except when using them as a separation tool under radar control.) We are required to follow our procedures; nothing in those procedures, AFAIK, suggests we "suggest" to aircrew on opposite GPS tracks that an offset right is a good idea. The presumption being that such flights shall always be separated by the appropriate vertical spacing. Fortunately, in the vast majority of cases, they are.

I've spoken with pilots who consistently report accuracy of a wingspan or less on GPS routes, as was tragically demonstrated by the collisions referred to above.

I totally support the idea of an offset being introduced in these cases, where it doesn't invalidate the airway separation being applied. Can't see how it would, in most cases.

It will, I think, fall to pilot's unions to make this one happen. Keep lobbying.

[4Greens]

Outside radar coverage, why don't you all just do it.

[Vee One...Rotate]

What, if any, are the arguments against offset tracks?

Cheers,

V1R

[Feather #3]

V1R,
There's a body called [AFAICR] the ICAO Separation Standards Panel who deal with this stuff.
It's made up of mathematicians and NIH phobes who live in the past. They assign equipment and pilot tolerances to all the sep standards. They don't sit day-in-day-out [or night...etc] watching potential mid-air's pass continuosly within a half-wingspan or less at 1,000ft separation. They haven't worked out that in the high 90 percentile, there is NO equipment error nor pilot error and if someone blinks, they'll hit.
Safety Heights [or whatever name you choose] are calculated by using traditional methods for flight legs [not talking RNAV stuff here]; by flying, say, 1nm right-of-track, all the world's S/H's have to be recalculated. They can't get it throught their heads that [see above] there is NO error with GPS [or, at least, so small as to be almost ignored....half-wingspan after 14hr flight?]
GPS was "made in America" and it would be absurd for ICAO to trust it and base anything official on it until the rest of the "World" catches up by moving to GNSS [bit like GMT and UTC, if you get my drift], THEN we can start to see something happening!:D The Poms have never really got over Decca not being used worldwide over Loran?
Rant over. We see P-RNAV now and maybe we're getting there. Roll on a 1nm right bias above FL200 as an FMC et al norm in LNAV!:ok:
G'day ;)

[4Greens]

Just do it!

[rab-k]

SLOP in NAT airspace is indeed an exisiting procedure, however the main difference between NAT SLOP and any in airways is that the problems are principally concerned with same, not opposite, direction traffic.

Informal studies done to determine the number of crews adopting it have indicated a single figure percentage uptake. Whilst attempts are being made to make crews more aware of the procedure with some operators actively encouraging their crews to adopt SLOP, I'm curious as to why so few apparently do - is it a reluctance to alter with the route held in the FMS, does it cause problems with waypoint cross-checking, does dispatch/ops have any influence or is it simply ignorance of procedures? Perhaps some here might offer an answer.

http://www.levelbust.com/articles/focus_aug_06_slop_files/image002.gif
Figure 1. The SLOP intends to spread aircraft out laterally with the use of two offsets to the right.From: http://www.levelbust.com/articles/focus_aug_06_slop.htm

[Zeffy]

...I'm curious as to why so few apparently do - is it a reluctance to alter with the route held in the FMS, does it cause problems with waypoint cross-checking, does dispatch/ops have any influence or is it simply ignorance of procedures?

No issues with waypoint checking -- once selected, the offset function is automatic. The waypoint list itself remains unaltered.

[rab-k]

Zeffy

Thanks, any offers as to what else might account for the low uptake?

[Giles Wembley-Hogg]

rab-K

In my view SLOP on the NAT tracks is more useful for avoiding wake than for avoiding collisions. The traffic flow is predominately one-way, so I can go months without seeing an aircraft going the opposite way to me and TCAS makes me aware of traffic going the same way. It seems pointless to offset on the off chance that someone is at the same level as me and going in the opposite direction undetected by ATC or TCAS or that an aircraft going the same way as me will be in the way for a few seconds as it or I change levels in an emergency whilst (inexplicably) disregarding the Atlantic Contingency procedures.

The reason I don't SLOP much myself is that 9 times out of 10 I need to offset LEFT to avoid the wake of the preceeding traffic and the current SLOP procedures have removed the ability to do that. In theory I am supposed to negotiate with the aircraft causing the wake to pursuade them to offset right, at which point the whole procedure becomes too much hassle for such little gain.

Bring back LEFT offsets and you might see more take up of the procedure. (In my opinion).

G W-H

[rab-k]

In my view SLOP on the NAT tracks is more useful for avoiding wake than for avoiding collisions - The reason I don't SLOP much myself is that 9 times out of 10 I need to offset LEFT to avoid the wake of the preceeding traffic and the current SLOP procedures have removed the ability to do that. In theory I am supposed to negotiate with the aircraft causing the wake to pursuade them to offset right, at which point the whole procedure becomes too much hassle for such little gain.

Bring back LEFT offsets and you might see more take up of the procedure. (In my opinion).

Excellent. Ta much.

Could you clarify a couple of points for me:

If the preceding traffic is on track centreline and you are sat in its' wake would you, independently of the traffic ahead, move one or two miles right to remain in smooth air, or is it your understanding that you hold your track centreline and must contact the other aircraft on 123.45 to request that they move?

Furthermore, why 9 times out of 10 would you require to offset left instead of right to avoid wake? (Not a pilot so apologies if this falls into the realms of a 'dumb-assed' question).

It seems pointless to offset on the off chance that someone is at the same level as me and going in the opposite direction undetected by ATC or TCAS or that an aircraft going the same way as me will be in the way for a few seconds as it or I change levels in an emergency whilst (inexplicably) disregarding the Atlantic Contingency procedures.

You'd be surprised! The 'joys' of a procedural environment is that you can't always tell who is doing what at any given time, particularly relevant if they are not doing what they should be doing which means we (ATC) can't always act immediately to resolve a problem. (Roll on ADS-B!). You'd also be surprised how many don't know the contingency procedures. I have witnessed a fair few examples of crews 'taking the law into their own hands', (for want of a better description), and not always as a result of a delay in ATC getting back to them. (Not being familiar with NAT procedures being understandable to an extent if only 10% of your sectors annually are NAT crossings).

Finally, the most alarming case I've ever seen in favour of SLOP was CAT over the ocean that induced a 1500' departure from the cleared FL of one aircraft, which twice passed through the level of the traffic above, (Going up and back down again). Fortunately, both had TCAS and were far enough apart not to cause more than mild alarm on the flight deck. (Heart failure in the Ops room mind you!). Afterwards, RVSM was suspended on that track and those too close for comfort were put back to 2K' sep'n.

My final question to those who are familiar with NAT crossings and SLOP: Do any of you offset as a routine or is it dependent upon traffic displaying on TCAS, traffic over/undertaking, traffic creating vortex or CAT?

[wiggy]

rab-k
As a frequent user on the NAT here's my take on this .
If there's nothing on TCAS I'll throw in the offset anyway, OTOH flying the 744 we often end up overtaking stuff and then, if there is proximate traffic I look at where they are and then modify or even remove any offset I'm using. Personally I'm uncomfortable we being directly above/below anyone, because of events such as the Turbulence encounter you describe.

I to would vote for the option to offset Left or Right.

[skiesfull]

SLOP has been in use (as a recommendation, not mandatory) over much of Africa for many years. It was introduced within the Atlantic OTS after wake turbulence reports, following the introduction of RVSM. It is also a recommended procedure (at least in my company) over Afghanistan. In my opinion, it is a useful procedure to adopt for GNSS -equipped aircraft, if only to counter those pilots who consider TCAS to be fool-proof in preventing mid-air collisions and removing the necessity to keep a good look-out. As for those who use SLOP only to find opposite direction aircraft passing directly above or below, possibly they are not GNSS equipped and have a less than accurate navigation system.

[Vee One...Rotate]

Feather #3,

Thanks for the info.

Rgds,

V1R

[410]

It seems pointless to offset on the off chance that someone is at the same level as me and going in the opposite direction undetected by ATC or TCAS ... and if just ONCE in your hopefully very long career, all the holes in the proverbial slices of cheese line up as they did in Brazil last year, you and all your passengers become a statistic.

A dead statistic.

Mods, could we resurrect the original articles on offsetting that used to grace the Home Page on the old PPRUNE? Or at least provide us with their URLs on this thread?

[Giles Wembley-Hogg]

410

I should have mentioned that the 767s I fly don't have a GPS feed to the Nav kit, so for your scenario to occur an awful lot of holes would have to line up.

For anyone who may have been concerned by 410s reply to me, without GPS the aircraft navigates using 3 Inertial Reference Systems which do not keep it on the centreline of the NAT track with the same accuracy as the GPS. A function of the IRS (lack of) accuracy is that a slight displacement is built in without any prompting by the pilot.

G W-H

[410]

Nothing personal, Giles; just standard debate.

Someone suggested it earlier: 1NM (or even .5NM) automatic offset above F200 whenever in LNAV mode for more than 'n' minutes would fix the problem. I know some deep thought would be required into just when this should be overridden, but anything has to be an improvement on the current situation where almost every aircraft passes within the wingspan of any opposite direction traffic.

Unfortunately, it would be years before any such system was certified, even if it was agreed to tomorrow, so the best we can hope for is for all regulatory authorities to follow the good example of India, Bangla Desh, Vietnam and the too few others and authorise SLOPS for all enroute traffic.

[Giles Wembley-Hogg]

410

I didn't take anything personally. I agree, a healthy debate is important. I just wanted to clarify a few of my comments and place them in the context of the equipment that I operate.

SLOPing is a good idea when operating in areas where there is opposite direction traffic. I wouldn't go to Africa without it. rab-k was asking about the NAT tracks, where for much of the day the vast majority of traffic is unidirectional. In these circumstances I believe that enabling both left and right offsetting would result in more people taking advantage of the procedure.

It is my belief that there is more risk on the NAT tracks from turbulence, wake etc than there is from opposite direction traffic.

In the European radar controlled environment I don't see any advantage to offsetting as we seldom follow the airway centreline as we are given short cuts, directs to downroute positions etc.

Since I only operate to Africa, around Europe and to the USA, my comments are limited to those theatres and in any case are just my thoughts.

All the best

G W-H

[rab-k]

I believe that enabling both left and right offsetting would result in more people taking advantage of the procedure.

Okay, okay, will someone please explain to the poor stupid ATCO that I am why this should be the case? Currently NAT procedures provide for 3 options, (Centre, 1nm RoT, 2nm RoT), and the take up is less than 10%. (Not my figures but from the link in my first post). What would '1nm LoT' or '2nm LoT' gain over the existing 3 choices that would result in more crews adopting SLOP, other than simply 5 options are better than 3 options?

(Thanks for replies BTW, keep em coming :ok:)

[Green Guard]

Even 1/2 of 1 NM (up to 2) is more then enough. Of course to the Right.

However when there is ONLY one way traffic,
per one track (Airway) like over North Atlantic
two airplanes can remain for hours one below the other on peculiar distance
a distance which would bring the traffic behind exactly in the downwash
(a wake turbulence ) of preciding traffic,
if BOTH are on center or offsetting for same distance,
(with certain crosswind component),

or if ONLY one is offsetting, but in case of downwash being drifted due to crosswind, to the side of a traffic behind.
:cool:
Wonder how geese can actually benefit from the same effect
=========================================================

[Zeffy]

What would '1nm LoT' or '2nm LoT' gain over the existing 3 choices that would result in more crews adopting SLOP, other than simply 5 options are better than 3 options?

Recognizing that the traffic separation statisticians have other rationales for SLOP, 5 options would still provide more effective wake avoidance strategies.

Current SLOP denies the option to fly left of track avoid the wake of an airplane ahead who is not offsetting.

Especially when the wind aloft is only slightly from the left, I'd prefer to offset upwind.

[rab-k]

I'm getting the impression that in certain circumstances, 2nm doesn't cut it with regard to moving clear of someone's wake, (even if you do manage to come to some kind of arrangement on 123.45), and that the extra mile(s) left may make all the difference.

However, I remain somewhat at a loss as to why >90% of crews don't routinely adopt the procedure, irrespective of wake. G W-H sounded as though he has additional issues if his 76' is triple-INS without a GPS feed, in which case perhaps some large % of flights fall within the "Aircraft without automatic offset programming capability must fly the centre line" category. But here once again, my being ground-based limits my understanding of the intricacies of various navigation systems. (Bring back our 'old' Fam-Flight scheme I say!)

I've checked both here: http://www.nat-pco.org/nat/Cont_Div_Slop.pdf

and in our own procedures, neither of which give a reason as to why offsetting to the left is not permitted. Perhaps, as suggested by Zeffy, the number-crunchers have their reasons, but if take up is so poor perhaps it is time they find out why and do something to address it, otherwise, why bother publishing the procedure in the first place!

Thanks again for your patience and replies.

[Zeffy]

...However, I remain somewhat at a loss as to why >90% of crews don't routinely adopt the procedure, irrespective of wake.

Without presuming to speak for anyone, might I suggest that GPS, RVSM and SLOP arrived in fairly close succession -- and there is a possibility that some pilots may still view SLOP primarily (or even solely) as a wake avoidance tool? (Ergo -- if there is no compelling evidence of a wake hazard, why bother to offset?)

Perhaps that, and human tendencies to resist change, avoid extra work (what, three or four key-strokes?!) might provide part of the answers?

[DenhamPPL]

..and in our own procedures, neither of which give a reason as to why offsetting to the left is not permitted.



I'm just a humble low-hours PPL (with a healthy interest in commercial aviation however!).

Could the "right-hand offset only" rule be due to the basic Air Law rules (at least taught to me here in the UK) that one shall (as a matter of good airmanship) stay to the right of any line features being used for navigation purposes to help prevent potential conflict with other aeroplanes following the same line feature from the other direction?

Whether that could include IFR on airways I don't know! Does someone?

Thanks for a very interesting debate. I'll creep back to my spam can now.

DenhamPPL

[skiesfull]

Some observations to the above posts:-
1/. SLOP is not mandatory
2/. If you wish to offset left, then why not ask/inform ATC of your reason?
3/. How will ADS-B work over oceanic airspace?
4/. If it will, then SLOP must be mandatory to enable separation to be reduced to 5 nms without radar coverage.

[pig dog]

DenhamPPL, you may only consider yourself as a humble PPL, but you are one of the few who have posted here that has grasped the concept of offsetting to the right only. This is to guard against a collision with opposite direction traffic at the same level as yourself. If you offset left and they offset right, then you may collide, if you are both offset right then you have an increased lateral separation, even if one of the aircraft is at the wrong level.

From my experience flying over India, Pakistan and Afghanistan outside of radar coverage (and with difficulties using the radio due to congestion, language barriers and poor reception) it is frightening how close opposite direction traffic using IRS (possibly with GPS updating) pass to each other. It only takes one of these aircraft to be at the wrong level with TCAS off and a disaster could happen. I think that it shows very sound airmanship to apply a right lateral offset whenever possible.

[4Greens]

I refer to my previous posts.
Tracking right of track outside radar coverage is simple,safe and effective. I find all the complex reasons for thinking about it a tad late in the day. It has been used for some time in less than well controlled airspace and is even procedure in many airlines. As I said before instead of worrying about it, just do it!

[rudekid]

Rab K

I always use an offset when flying through Iraq, Africa and Afghanistan. However, using my FMS (which is GPS/INS though not latest generation) this is a time consuming business.

As a function of the user directed flight plan, my kit will happily track right or left of track automatically. However, it also wants to overfly the flight plan waypoints directly and the offset falls out at each leg transition. Therefore, the autopilot makes a hard turn for the points about 2 miles to go and hard turns back to regain it's next track. At that point I need to set up the next leg offset and you guessed it- now the kit is off track and turns hard to regain it's offset! Now, none of this makes for a smooth ride!

Altough none of this is difficult and is easily overcome by judicious fiddling with the autopilot (or even, God forbid) manually flying the aircraft, there are circumstances where it's easier to let the autopilot do its own thing and accept I'm not offset.

I'm a military driver, but my FMS is commercial, off the shelf and common. In a busy european airspace environment, I can easily see where the a crew would be too busy to utilise this feature of the FMS.

Regards

RK

[Giles Wembley-Hogg]

rab-k

The FMS does allow an offset to be flown, but since the IRSs are not as accurate as GPS, the aircraft flies a fairly random straight line over the ocean. This is rarely the same straight line as another aeroplane even if we are both notionally on the centreline.

I believe Zeffy is right. In the absence of any significant volume of traffic travelling in the opposite direction on the NAT tracks, SLOP is primarily a wake avoidance tool. This is why I believe left offsets should also be allowed.

I don't believe that allowing larger offsets to the right will increase take up, because pilots will be wary of positioning themselves at any distance downwind from wake producing traffic. Wake can be surprisingly persistant, invisible and unpredictable.

DenhamPPL

You are right about the reason for only offsetting to the right in the general case, but I believe that the Atlantic is such a uni-directional flow that it falls outside the general case.

G W-H

[rab-k]

Rudekid

Thanks. That explains the ADS reports we sometimes see when a flight passes a waypoint, for example 52N020W routing to 53N030W, NEXT 52N040W, and having reported at 20W we see something like 5208N02115W 5301N02959W NEXT 5201N03959W appear on an ADS report - this would be the offset for the next leg being entered, correct?

SLOP is primarily a wake avoidance tool.

Thanks also. Just so I'm clear on this, is that how you interpret the procedure, or how you apply the procedure?

[Giles Wembley-Hogg]

rab-k

I think that I understand you question. Forgive me if I've misunderstood, but this is my understanding:

The latest FODCOM I have to hand regarding the procedure is 26/2004. This basically explains that the procedure is designed to spread aircraft over 3 positions laterally to reduce the risk of midair collisions following an altitude deviation. The FODCOM goes on to show disappointment that more crews do not take advantage of the procedure. It also implies that use of the procedure to avoid wake is both acceptable and desirable.

On a practical level, and accepting that in the event of an altitude bust "a miss is as good as a mile", since the aircraft I fly does not maintain the centreline with great accuracy, aircraft at different levels fly at different speeds and the number of aircraft that I overtake/overtake me on a crossing is typically no more than 4 or 5, it appears to me that the risk of an altitude deviation causing an actual collision is very low.

On a practical level, a wake encounter is both dangerous and more likely than an altitude deviation caused collision. Even fairly trivial wake encounters are uncomfortable for crew and passengers alike. For this reason I would contend that pilots in the main use SLOP to avoid wake. Since we are only allowed to go to the right now (left and right offsets were allowed in the original trial), if the wind is blowing in the wrong direction staying on the centreline will become the preferred position for all the traffic following a wake producing aircraft on the centreline. Thus by only allowing right offsets I believe that the number of pilots taking up the procedure is restricted by the inflexibility of the procedure itself.

Looking at it from the other side. If we could offset both ways and thus more people took up the procedure, the statistical reduction in collision likelyhood would be achieved.

Just my thoughts

G W-H

[W Weasel]

This whole issue of “offset” is really an interesting argument. There are a number of issues and I fully understand each and everyone one of them. Some mention offsetting in order to reduce collisions, others mention wake and still others discuss the fact that it is really not a valuable practice.
I will begin to state that except in a few areas I offset for all the reasons mentioned. Someone as old as I and in the industry as long remembers a different era. Yes I have made crossings using celestial navigation “cel-nav” with navigators, OMEGA navigation, INS navigation, Triple Mix IRS only navigation and IRS/GPS navigation. The only type of crossings (Atlantic and Pacific) I have not done was old Chuck’s needle, ball, airspeed crossings in the Spirit of St. Louis.
The one thing you can see is the accuracy of each type of navigation improves greatly from its predecessor. Normally this is a good thing (and I have no complaint) however, the issues brought up above are just the penalty we pay for such improvements. Let me ask a fundamental question: “How wide is a normal airway?” Not a NATS or Pacific Track but a normal airway anywhere in the world?
MNPS, RVSM, FANS all contribute to the help of the system but they also provide (once again) a direct link to the problems. Whether it is the speed of Sat voice, data link or HF, to the wake avoidance in NAT MNPS, the problems are created by this progress.
In the old days a navigator was great if he could get you within half a dozen miles of where you wanted to be. Then the slow (built for submarines in the early days of the cold war) Omega would get you within a few miles of that same point (especially in areas other than the NATS and forget above 60 degrees North or South.) Then we all remember following that B-747 classic with its amazing INS that was good to within a mile. Follow that closely with the triple mix IRS and you were now down to hundreds of feet. Well now we fly around with 777s, A330s, 340s, and a host of other GPS/IRS aircraft that get us under a half of wingspan from our fellow pilots in that RVSM airspace.
So my question, how wide is an airway? Yes we all know that RNP5 (and even RNP1 for approaches) requires accuracy within 5nm of the centerline for at least 95% of the flight time; however, how wide (even with RNP5) is the airway?
So why in the world do you want to stay smack dab in the middle of the road – accuracy? Forget about the NATS or Pacific for in the most part you are dealing with one way streets (except for “off tracks.”) How many times have you flown across the Arabian Sea, Australia and soon Africa when you had a closure rate of 12-15 nm per minute? You and your traffic are 1000 feet (+/- 95 feet) apart. Do you really want to be “smack dab in the middle of the road?” How wide is the airway?
http://www.faa.gov/ATS/ato/status_ww.htm:) :)
Now why in the world do we offset 1-2 nm right of centerline? I know it says so in Jepps (and many ops manuals) but why? If I am heading 090 and the wind is 020 at 100 knots, in the scenario above do I want to offset 1 nm right? Every inch of that traffic’s wake is going to fall right on me. Why not 1nm left?
Now I know I have had many discussions with my F/Os who rightly ask. “Well if I offset 1 left and the opposite traffic offsets 1 right, then we are wingtip to wingtip again.” Of course, so why not if you are offsetting for wind/wake, offset 2 nm and for collision avoidance 1 nm offset? Whether it is left or right you are STILL ON THE AIRWAY and add a large degree of protection from altitude errors and wake turbulence. This way you will always have BOTH areas covered. How wide is the airway? In those old days we were always offset anyway due simply to inaccuracies, now those inaccuracies are largely gone and we (as pilots) must compensate for the engineers, lawyers and aircraft manufacturers that forgot. Remember we are pilots not parrots!
Burners and out!

[W Weasel]

This whole issue of “offset” is really an interesting argument. There are a number of issues and I fully understand each and everyone one of them. Some mention offsetting in order to reduce collisions, others mention wake and still others discuss the fact that it is really not a valuable practice.

I will begin to state that except in a few areas I offset for all the reasons mentioned. Someone as old as I and in the industry as long remembers a different era. Yes I have made crossings using celestial navigation “cel-nav” with navigators, OMEGA navigation, INS navigation, Triple Mix IRS only navigation and IRS/GPS navigation. The only type of crossings (Atlantic and Pacific) I have not done was old Chuck’s needle, ball, airspeed crossings in the Spirit of St. Louis.

The one thing you can see is the accuracy of each type of navigation improves greatly from its predecessor. Normally this is a good thing (and I have no complaint) however, the issues brought up above are just the penalty we pay for such improvements. Let me ask a fundamental question: “How wide is a normal airway?” Not a NATS or Pacific Track but a normal airway anywhere in the world?

MNPS, RVSM, FANS all contribute to the help of the system but they also provide (once again) a direct link to the problems. Whether it is the speed of Sat voice, data link or HF, to the wake avoidance in NAT MNPS, the problems are created by this progress.

In the old days a navigator was great if he could get you within half a dozen miles of where you wanted to be. Then the slow (built for submarines in the early days of the cold war) Omega would get you within a few miles of that same point (especially in areas other than the NATS and forget above 60 degrees North or South.) Then we all remember following that B-747 classic with its amazing INS that was good to within a mile. Follow that closely with the triple mix IRS and you were now down to hundreds of feet. Well now we fly around with 777s, A330s, 340s, and a host of other GPS/IRS aircraft that get us under a half of wingspan from our fellow pilots in that RVSM airspace.

So my question, how wide is an airway? Yes we all know that RNP5 (and even RNP1 for approaches) requires accuracy within 5nm of the centerline for at least 95% of the flight time; however, how wide (even with RNP5) is the airway?

So why in the world do you want to stay smack dab in the middle of the road – accuracy? Forget about the NATS or Pacific for in the most part you are dealing with one way streets (except for “off tracks.”) How many times have you flown across the Arabian Sea, Australia and soon Africa when you had a closure rate of 12-15 nm per minute? You and your traffic are 1000 feet (+/- 95 feet) apart. Do you really want to be “smack dab in the middle of the road?” How wide is the airway?

Now why in the world do we offset 1-2 nm right of centerline? I know it says so in Jepps (and many ops manuals) but why? If I am heading 090 and the wind is 020 at 100 knots, in the scenario above do I want to offset 1 nm right? Every inch of that traffic’s wake is going to fall right on me. Why not 1nm left?

Now I know I have had many discussions with my F/Os who rightly ask. “Well if I offset 1 left and the opposite traffic offsets 1 right, then we are wingtip to wingtip again.” Of course, so why not if you are offsetting for wind/wake, offset 2 nm and for collision avoidance 1 nm offset? Whether it is left or right you are STILL ON THE AIRWAY and add a large degree of protection from altitude errors and wake turbulence. This way you will always have BOTH areas covered. How wide is the airway? In those old days we were always offset anyway due simply to inaccuracies, now those inaccuracies are largely gone and we (as pilots) must compensate for the engineers, lawyers and aircraft manufacturers that forgot. Remember we are pilots not parrots!

Burners and out!

[410]

See http://www.pprune.org/forums/showthread.php?t=15713&highlight=Lessons+Delhi
and http://www.pprune.org/forums/showthread.php?t=36382&highlight=Lessons+Delhi
Unfortunately, my original “Lessons from Delhi” post is now buried deep in the PPrune archives. It used to reside in the Safety page on the Home Page, but was lost in the latest revamp of PPrune.

It probably needs to be re-stated that the situation on the North Atlantic is somewhat different than the rest of the world – offsetting there is primarily a wake avoidance tool, whereas everywhere else, it is primarily an anti collision/anti-screwup tool. And I agree that left offsetting would be safe(ish) on NATS, but the poor bloody regulator would never be able to bring it in for fear of the confusion it would guarantee when someone would try left offsetting elsewhere. (I’ve actually had an FO insist that if we flew right offset outbound, we would have to fly left offset on the way home – and he’s a captain now, and I think he’s still convinced he ‘one upped’ me well and truly with his clever logic!!)

Re right offsetting not always working on NATS tracks: I spent four hours yesterday getting repeatedly hammered by the wake of the aircraft in front of me on NATS. The winds were strong but variable and slightly from the left, and we tried on track, one mile right and two miles right - and the wake turbulence kept finding us! One mile left would have fixed the problem – or if he would have just stuck himself out to two miles right, but CPDLC and the ‘great silence’ makes it a bit difficult to identify the culprit. I didn’t try the 123.45 talkathon to find him.

[W Weasel]

My discussion was purely designed for all world situations; however, on the NATS you have far MORE leeway than in most places on this tiny planet called Earth.

“I spent four hours yesterday getting repeatedly hammered by the wake of the aircraft in front of me on NATS.” I honestly ask, with all respect, WHY in the world would you do this? You are commander or your aircraft and under EVERY regulation in the world you are ALLOWED to deviate from any regulation for the safety of your passengers, crew and aircraft. Flying for hours (or for four hours) is not only bordering on negligence but from a commercial point I hope it was not my company and my profit sharing!

The NATS are NOT different from the rest of the world, if fact they are far more lenient than the rest of the world. Your F/O was probably right (assuming the winds were the same when coming back as they were going.) His clever logic is in fact pure logic. A left cross wind outbound is (assuming no change) a right cross wind inbound. Why would you want to fly downwind back home and get “hammered by the wake of the aircraft in front of [you] on [the] NATS?”

As I stated in my previous post, I know it is not common logic to go against manuals etc. but folks come on. If I fly 1 nm offset right when avoiding potential conflict, and that is upwind; then why not fly offset UPWIND 2 nm when flying in the opposite direction? I avoid conflict and I avoid wake.

The only potential fallacy in this logic arises when you consider the GUY below you. In that case (for wake) HE has to have TCAS ABOVE and not below. Therefore, he sees you coming long ahead and can make corrections accordingly (i.e. offset another mile to let your wake go downwind of him in a crosswind situation.) You old timers remember before the days of TCAS when we painted the target with the radar – we knew how to spot and split long before he arrived!

Come on guys this is not brain surgery, but piloting - constant small corrections (like a hand flown ILS.) The NATS are simple, try taking with Mogadishu Africa, Mumbai India, Karachi Pakistan, Xizang China, Kabul Afghanistan, Xingjian China, or Mansus Brazil control on HF and get a simple change or altitude verification. “Standby I’ll call you back” is great compared to ignoring your request!

“…but the poor bloody regulator would never be able to bring it…” Come on, you know the words; this is ABC flight 123 declaring an emergency. I’m turning left 30 degrees to avoid a buildup!” Are you going to fly into the cell because the “regulator” the ATC facility, the African or Indian controller won’t answer you? Are you going to be the Captain of flight 612?

“Honored Pilot of Russia Vladimir Gerasimov blames Kharkov Air Traffic Control (Ukraine) for the crash of Tu154 in Donetsk Region (Ukraine) on August 22, Izvestia newspaper reports. According to Gerasimov, the Ukrainian air traffic controllers, who were working with the Anapa-St. Petersburg Flight 612, did not permit the crew to deviate from the air corridor by more than 20 kilometers to avoid the thunderhead.”
http://www.regnum.ru/english/dossier/61.html

Come on guys, we are not parrots, we do not regurgitate Boeing FTMs, FCOMS etc - we fly airplanes - we are pilots.

Burners and out!

[rab-k]

One mile left would have fixed the problem – or if he would have just stuck himself out to two miles right, but CPDLC and the ‘great silence’ makes it a bit difficult to identify the culprit. I didn’t try the 123.45 talkathon to find him.

This applies to all - please DO NOT HESITATE to ask us to I-D the traffic for you, ask them to listen out or contact you direct on 123.45, or even simply relay a message on your behalf. Subject to traffic, we can also try to increase the vertical separation between you and the traffic ahead to try and reduce the effect. Don't feel you must sit in silence for hours on end, whilst getting your ear bent by the CSD because two dozen SLF up the back now have hot drinks in their lap.

Perhaps the stat-analysis bods will prick up their ears when the A380 starts crossing the pond. They already require 2000' even in RVSM between themselves and the next guy beneath, so 2nm to the right might not even cut it with the wake these guys will create.

What I would ask is that if any of you feel strongly enough about not being able to offset left, which by the sounds of it some do, CHIRP it. ( http://www.chirp.co.uk/ ). Nothing will be done if the powers that be don't hear about it.

Thanks again :ok:

(PS Feel free to pop in anytime you're passing: http://en.wikipedia.org/wiki/Shanwick_Oceanic_Control )

[SR71]

In my view SLOP on the NAT tracks is more useful for avoiding wake than for avoiding collisions.

Judging by the number of wake encounters you've had, one wonders how many collisions you've had?

:ok:

[skiesfull]

410
Why did you not ask ATC via CPDLC or HF to offset left of track due wake turbulence? ATC is a service to pilots - if you don't ask they may not offer - especially on procedural control. I'm sure that you would have notified ATC of your intention to deviate left of track due Cb ahead? I would be very unhappy sitting with you or behind you for 4 hours in wake turbulence, when there was an obvious solution to hand!