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Odd Flight Levels Westbound

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Odd Flight Levels Westbound

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Old 11th Jan 2019, 18:15
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Odd Flight Levels Westbound

A question about the dynamics of this incident, which shows something I've never experienced, but I haven't flown in all ATC jurisdictions.

Incident: Wizz A320 near Madrid on Nov 10th 2018, descent below cleared level causes near collision

Incident begins with two aircraft straight and level - westbound - at FL310 and FL290. Usually I'd expect westbound aircraft to be at "even" flight levels 280, 300, or 320, for example. Although the primary rule in Class A is "what ATC assigns," of course.

Is this just because the aircraft are closing on 110nm to destination and for ATC purposes are in a preliminary descent? Would the RVSM floor of FL290 be a factor (as low as possible while still allowing RVSM-rules flexibility, regardless of direction)?
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Old 11th Jan 2019, 18:27
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Some places have a north/south division rather than east/west due to traffic flows. France is one and I think Spain might be the same, as I recall it’s then south-odd north-even.
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Old 14th Jan 2019, 19:21
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Thanks - I was just waiting to see if other explanations surfaced, but yours is fine!
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Old 16th Jan 2019, 19:09
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From what I gather then the aircraft was descended to the safe level of 1000’ on top of the other aircraft. For whatever reason he bust his level.
Although west/east levels still exist, nowadays ODLs are the norm & a lot of the time don’t need to be co-ordinated with the next sector or unit. We use them as an aircraft’s requested FL might not be available so you give them the next best level whether it is correct direction level or not, and also due to the increase in traffic in complex airspace then you sometimes need to use ODLs.
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Old 16th Jan 2019, 19:44
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ODLs have been in use for over 40 years; I often handled traffic at 330, 350, 370 all going the same way (westbound) when I was at Lindholme controlling upper airspace traffic in '73.
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