Offset, left or right?

[ManaAdaSystem]

No, this is not a question of if or why or how much or whatever, but I was under the impression that those of us who fly offset, do it to the right. Until recently, when I started to meet aircraft flying offset to the left.
Can we please agree to offset to the right?

[Capt. Crosswind]

I believe the convention was established during WWII and is as you describe to the right . It may have its origins in the International Regulations for Preventing Collisions at Sea where ships from opposite direction pass Port side to Port side in a fairway, and keep as near to the outer limit on the starboard side as is safe & practicable. The IRPCS were of course the basis for the Air Nav Regs when formulated.
This procedure has saved me from a mid air (or a very near, near miss) over Masirah Island (off Oman) circa 1981.

[Captain Stable]

Port Said? You wanna buy dirty postcard? ;)

Offsetting to the left is a ludicrously dangerous act. As Capt. Crosswind points out, tradition started offsetting to the right. Anti-collision turns are always to the right. When VFR and following a ground feature (e.g. railway line or road) you offset to the right.

[Nugget90]

This could be a very well kept secret, but ICAO have published guidelines to States about lateral offsets: these can be found in State letter AN 13/11.6-02/21 - a revised version being published on 31 May 2002.

In this letter, the guidelines state very clearly:

"The offset should be applied to the right of the centre line relative to the direction of flight." (with 'right' in bold.)

The guidelines make it clear that pilots should not apply offsets unless the State has decreed that it is alright for them to do so, how accurate the on-board navigation equipment must be, and how large the offset may be (normally not more than 1 nm).

[Capt. Crosswind]

Looks like it is a well kept secret you've unearthed, well done Nugget90.
Maybe this is one for IFALPA Technical to ensure is promulgated before there is an incident/accident.

[HEATHROW DIRECTOR]

Anything which promotes air safety is commendable and I've heard of "offset" pilots for the last 35 years so there's nothing new in it. However, what does one do in holding patterns? I sat yesterday afternoon watching the Heathrow holding patterns, which were full for hours on end. The accuracy with which holds are flown is quite amazing - I've often seen 3 or 4 a/c in a hold so vertically aligned that they looks like one aircraft..

[Capt. Crosswind]

My understanding is that offset does not apply to the
terminal area, but only to en route ops,where a 1 nm offset is still well within the airway.
For VFR ops it applies to line features such as roads,railway lines,rivers,coastlines etc as mentioned by Capt Stable.
In the terminal area one should fly track centre line, plus or minus a gnats whisker.

[vanman]

Why is this even a debate? Tradition is set in stone - all we did is forget about it for a while when the NAV kit got more accurate. You can't reinvent the wheel.

[Captain Stable]

HD, offset navigation does not apply to the hold, or anything else in terminal navigation. I don't know anyone who would have the faintest idea how to fly an "offset hold". It only applies to enroute flying. Hope this helps you.

[RadarContact]

Well, I've seen a few offset holdings myself, but I don't think they were intentional...

[Nugget90]

Further to my earlier contribution, the Summary of the Use of Lateral Offsets specified in the ICAO State letter reads as follows:

When considering the use of lateral offsets to enhance safety, the following conditions should be taken into account:

a) offsets should only be applied when approved by the appropriate ATS authorities;

b) offsets are only to be applied in oceanic or remote airspace;

c) the magnitude of the offset should not be more than 1.9 km (1 NM) from the route centre line;

d) the offset should be made to the right of the centre line relative to the direction of flight;

e) the offset should be applied only by aircraft using GNSS navigation systems; and

f) offsets should not be applied in parallel route systems when the route spacing is less than 93 km (50 NM).

These guidelines do not preclude the implementation of lateral offset procedures which differ from those described above. However, in such circumstances:

a) offset tracks left of track are not to be used: and

b) a safety analysis of the proposed procedures will be required.

It is recommended that these offset procedures only be implemented on a regional basis, after coordination between all States involved.

[ManaAdaSystem]

A lot of "nuggets" from you all. Thanks!
Last night it happened again, we met 2 aircraft flying half a mile LEFT of track. Airway over the sea, and only a (bad) HF connection.
Maybe the two of you who have voted left of track could explain why? Assuming you are pilots, of course.

[Pegasus77]

Not every aircraft has the same exact navigation-possibilities. The A319 and A321 I fly at work have GPS on board, the A320s don't, which means, you fly more exact on the airway, usually, in the 319/21 than in the 320.

On the main land we always joke about Brits flying to the left of the track. :D

My best guess is when you see airplanes flying half a mile off to the left, their IRSs have run away a little bit, especially over the sea, where you cannot make a radioupdate. You could always try 121.5 or 123.45?

P77

[410]

ManaAdaSystem, I’ve seen more than a few aircraft pass to my right, even when I’m flying right offset myself. I think (or at least hope) that in most such cases, the aircraft is on a direct track, has a different nav. data base, or is regaining track after weather avoidance.

I’d like to see an offset automatically embedded into every FMS, requiring no pilot input at all, for all VNAV tracks when a GPS-equipped aircraft is above 10,000’. If an aircraft is called upon to take up a heading, it’s not in LNAV, so it goes exactly where the ATCO asks it to go, without the offset. However, when it returns to LNAV tracking, the FMS will automatically fly offset. On descent, passing through 10,000’ the offset would be automatically removed.

Another, possibly better way to achieve this would be to use the existing protocols in existing FMS equipment – ie, the offset kicks in at the end of the SID and is removed at the beginning of the STAR, at whatever altitude that may be – and if there is no SID or STAR, the 10,000’ climb/descent ‘gate’ is used.

It shouldn’t take too much imagination to recognise that particularly with the introduction of RVSM, the recent tragedy in southern Germany is quite likely to happen again, most likely with opposite direction traffic on the same airway rather than with crossing traffic, (which only occupies the same path for a split second).

I’ve just returned this morning from a flight through Europe where I had four aural TCAS traffic alerts in two sectors. One of these was from an aircraft climbing too steeply to its assigned level 1000’ below mine. After it had passed me, I saw from its TCAS return that it busted its altitude by 400’, coming to within 600’ of my level – and of course, exactly on my track. If we’d both been flying offset and his altitude bust had been even more extreme, neither of us would have been required to carry out a Resolution Alert manoeuvre and the chances of a tragedy would have been far less with both aircraft maintaining their autopilots engaged.

Forget about the ‘whys’ of the recent tragedy over Germany – it has all too clearly illustrated what happens when only one of the pilots involved in a TCAS RA encounter does not follow a TCAS command immediately and to the letter in an RA.

I recognize that if ICAO decided to introduce automatic offsetting tomorrow, (faint hope), it would take years to be implemented, so in the meantime, I’d like to see ICAO authorise manual (pilot input) offsetting for all operations above 10,000’ with an official set of rules and guidelines. I can see that this suggestion would horrify many ATCOs who work the crowded skies of Western Europe, (but where did the last tragedy occur?), so if that’s too big an ‘ask’, let’s at least be allowed to do it in other areas that are recognised as being less efficient than the systems in Western Europe.

Wouldn’t it be nice if, just this once, we slammed the proverbial stable door before the horse has bolted? – ie, before ‘n’ hundred more people are killed?

[SuperRanger]

nugget,

would you know if a copy of this letter is avail on the net?

SR