Any issues flying small offset to airways route?

[Blip]

Can an ATC person explain to me what issues if any there would be if pilots we allowed to fly slightly offset from an airways route.

Flying from the west coast to the east coast of Australia at 37,000 ft in a B737-NG and passing directly under an opposite direction B737-NG with only 1,000 ft separation doesn't seem very smart to me.

What if we were able to or even required to pick a number between 0.1 and 0.9 nm as an offset to the right. This way if a mid air collision does occur it will be by chance, not by design!

Driving on the left-(or right)-hand side of the road to prevent head on collisions between cars travelling in the opposite direction makes perfect sense to everyone. Why not add that extra layer of protection to airliners with a combined closing speed of some 900 knots?

[055166k]

Blip
Why not ask ATC if they mind? It will save the controller having to ask "do you know you're flying xxxx right/left of track?"
Doesn't happen these days but some of the early INS equipped traffic off the ocean would sometimes slip the odd mile or so. Some ATC buddies may recount the requests to overfly a beacon as a last nav-fix before the crossing.
In UK certain sectors use a radar monitored traffic separation without imposition of assigned headings.....the specified routes structure [where this is permitted] does require that such traffic follows the published route or is vectored on the "safe" side of the track.
Early considerations of using track offset capabilities of modern a/c took a knock when it was realised that different systems normally use different turn anticipation criteria, it may work on a fairly straight sector but turns are less than safe.......in UK we are aware of the Airbus family turn which is very early indeed and goes nowhere near the beacon.......and so it is not used for separation. A few controllers may use the facility to help set up a sequence or tactical position but using just offset for separation is forbidden, a recognised separation method must be used when appropriate.

[tobzalp]

In OZ over the GAFA, you are not on radar so fill your boots. On radar, 0.1 nm is not noticable so fill your boots. 1000ft is a standard so what is the problem?

[Blip]

Just to clarify, I'm talking about offsetting without a specific clearance from ATC to do so.

tobzalp. There is no problem with 1000 ft separation, but I used the road analogy for a reason. What do the two cars in my analogy have in common?

I know that aircaft such as the B767 and B737-400's (that have IRU's and FMC's without GPS position updates) often have an ANP up around 3 nm when they haven't had a DME or VOR position update for a while. This is always the case on Australian transcontinental flights. For this reason I personally don't see the problem with offsets of less than 1 nm for aircraft that do have GPS updates.

I suppose I am wanting to start a discussion on this subject because at the moment it is not standard practice to offset when outside radar coverage, and I think it should be.

Why do we choose to have two airliners with GPS position updates, flying towards each other at a combined speed of 900 knots outside radar coverage with absolutely no lateral separation (not even a wingspan) and relying soley on vertical separation for collision prevention??

[Strepsils]

What do the two cars in my analogy have in common

They're at exactly the same level?:hmm:

If we all follow the rules then shouldn't be needed, but as mentioned, anything less then a mile and the radar controller probably won't notice it, never mind mention it. When procedural, fill your boots, no one knows what you're up to.

Then again, what if you offset a mile to the left and the oncoming offsets a mile to his right? You're no better off, are you? ;)

[Blip]

Then again, what if you offset a mile to the left and the oncoming offsets a mile to his right? You're no better off, are you?

Indeed! That is why I propose we pick a random number between 0.1 and 0.9.
By doing that, we have just reduced the chances of a head on collision by a factor of ten. (On second thoughts make it a number between 0.1 and 1.0. Oh what the heck. Make it 0.5 to 2.0!) WHATEVER!

If we all follow the rules then shouldn't be needed

Yes, but ****e happens. Nobody knows what happened over Brazil, but look at the outcome. No doubt the result of multiple factors all lining up in a row. This is just one more factor (no offset) that simply doesn't need to be there. How many sectors were flown around the world between the last five collisions between jet traffic. Millions? Your chances of being involved in a collision are minute in the extreme, but that is no comfort to those people that ended up dead in the Amazon forest this week, or those children that were killed in the TU-154 over Germany in 2002.

I am happy to "fill MY boots", but what about the rest of us. What about when I am paxing on holidays and I'm sitting on the other side of the flightdeck door. I hardly think it would go down well with the captain if I slip him/her a note urging him/her to offset a little bit so that I might enjoy my movie with peace of mind.

It needs to be written into the AIP and become standard procedure so that I don't have to explain myself everytime I go flying and wonder if the guy next to me is feeling uncomfortable because we are not following the letter of the law.

Where is the logic in not offsetting?

[Blip]

And sorry if it sounds like I'm having a go at ATC. That is certainly not my intention.

I am the first to admit that on every flight, I make mistakes as does the other pilot next to me on the day. We are only human.

I just wanted to consult ATC'ers to see if there is any objection to my proposal and explore the reasons why.

Thank you.

[Spodman]

In Oz rules pilots only have to report to me if they are more than 1 NM off track. If you fly a 0.9 offset I will not know it... unless you are ADS/C equipped when I will recieve an ADS track non compliance alert on my screen and will have to vary your clearance.

Do you go left or right? Does it depend if you are used to driving on the left or right side of the road???

[SM4 Pirate]

Do you propose offsetting left or right? How does a track offset fix anything but opposite direction issues. You may trust your gear to be .1NM or .9NM off track; how does it compare with the bloke coming the other way, how good is his gear? Your offset may match the error in the aircraft coming the other way, thus your offset is worth less than being on track?

The "Überlingen" crash involved effectively a 90 degree cross, unfortunately the worst thing possible happened, but offsetting would have resolved naught.

In a perfect world we'd have no opposite direction tracks; but what exactly are they? 5 miles apart, 10, 15, 20, 30, 50, we've got variations of all those. The route structure over the 'Bight' is supposed to assist segregation and separation, but often does nothing in terms of 'separation'; throw in one grey puffy thing that you want to fly around.

Let's not mention 'user preferred routes', 'flex tracks', 'free flight' or 'direct tracking' in terms of this stuff.

Your self initiated offset may assist with opp direction traffic (on your route only), but put you in it with any type of crossing traffic or other method of nav going the other way. So even if everything was "perfect" (all gear very accurate) and everyone was flying .7NM (say) Left, only the truly opp direction stuff is sorted with offsets.

ATC separation standards are supposed to provide 1NM (basic) separation (longitudinal, time, lateral etc.) or the relevant vertical standard; Tolerances are wide and varied depending on ground based equipment and the quality and serviceability of the airborne gear.

I think it is far too simplistic to say an offset = increased life expectancy as you're not the only player in the equation. That said it probably would go unnoticed and wouldn't hurt, even if it won't fix all.

[Tarq57]

Blip, I'm a tower controller with a (non-current) area rating. Spoken to a few pilot friends and this has come up a few times. On exact reciprocal routes, or same direction routes, using gps, the passing of another a/c below occurs with sufficient accuracy that the radio altimeter notes the passage.
So, not speaking for other nav systems, or crossing routes, but a few of the guys I know have said they always offset 200metres right. (Maybe 100,maybe 250, can't remember, but it was something like that.) Why right? Common sense. Rules of the air=keep right. Nobody is fooling themselves it's a separation standard; it's simply a mechanism to hugely reduce the chance of a meeting of metal on exact recip routes should for any reason the vertical space be zero.
ATC is not going to notice it on the displays.
ATC is not authorised to approve it, either, so I would imagine most of us would be happy not to officially know it's being done.
One of those things that seems to make sense. (For this specific case.) I don't know of a procedure or separation standard that would be invalidated by flying 200metres offset. But .9 of a mile....?
Best bet I reckon is to go through your union technical rep to try and get an approval effected with regulatory blessing. Otherwise, one day, the holes will line up in another way, and although pure bad luck, that being 200m off track might just be enough to cause the midair, and guess what they'd say then.

[120.4]

Blip
This is an eminently sensible precaution now that airborne navigation has become so accurate that radar altimeters will pick up an underflying aircraft. One of NATS' biggest safety concerns is level busts and should one occur during opposite direction airborne navigation at this degree of accuracy there is little between us and disaster. To me this is an example of good airmanship which ought to be encouraged. When on your own navigation, 250metres is absolutely nothing to ATC; anybody who is relying on that 250m for his separation is acting unwisely.
However, so as not encourage a reckless attitude to ATC instructions generally, this is not appropriate or necessary when under ATC vectors. For example, the LTMA approach sectors work to zero tollerance on traffic spacing. Into strong winds we quite often deliberately "erode" radar separations on the base legs so that we can get traffic tightly spaced on final. Applying a tolerance to the heading or speed instructions is not acceptable.
Just last week I had Far Eastern traffic (with a brit voice) reduce from 180kts to 165kts when into wind on base leg at about 12nm from touchdown. (The traffic following him was on the opposing base and had a 30kt tailwind.) The mode S showed me he had reduced and when I asked he said "we have slowed to 165 is that alright?" I said "well no actually, I now have traffic behind you that is too tight." I was forced to take this traffic (and the subsequent) through the centreline to maintain vortex spacing and in concentrating on that priority I was wide on the one behind that. Immediately I noticed this guy's indicated speed come back up to 180 so it is not as if he HAD to slow down for technical reasons.
All the guys I know here are sympathetic to the different speed equirements of the varous types, eg. B757s and BA46s being slow and B773s being fast. We have noticed over the past few years that more and more aircrew are advising us early if they have a particualrly fast or slow Vref and this is to be encouraged; doing your own ATC isn't.
Point 4