I did some research and minimum vertical separation used to be 2000ft but it changed to 1000ft in 2002 and they want to change it to 500ft on american territory. Is this correct? Why they wouldn't change it to 500ft on European territory also ?

2nd question:if aviation is evolving yearly, then airspace is getting more and more crowded. there is Concorde who has retired but used to fly at 60.000ft for example, why instead of designing new aircraft to fly higher, they would reduce the service ceiling ? I heard that from an engineer but I don't find an explanation. Statistically, they are reducing the service ceiling. Can anyone give an opinion? example? Thanks.

  • $\begingroup$ It's a little unclear what you're asking. How are they "reducing the service ceiling"? If you're asking why they don't make airliners that fly at 60,000 feet there are numerous engineering challenges involved. $\endgroup$
    – TomMcW
    Apr 6, 2018 at 18:35
  • $\begingroup$ The way I understood it is that if an A320 service ceiling is 41000, they will soon or later make another aircraft that won't have higher service ceiling in fact it will have the same abilities (fuel consumption, speed etc) but will have lower service ceiling. $\endgroup$ Apr 6, 2018 at 18:41
  • $\begingroup$ I haven't heard anything like that. The two latest large airliners to come out, Airbus A350 and Boeing 787 both have a ceiling of 43,000 ft. That's pretty much going to be the limit without going supersonic and there are several questions on the site addressing the additional problems of building supersonic airliners $\endgroup$
    – TomMcW
    Apr 6, 2018 at 18:47
  • 3
    $\begingroup$ You might want to split these into two separate questions. The second one is related to: Why are many jet aircraft designed to cruise around FL350-370? $\endgroup$
    – fooot
    Apr 6, 2018 at 19:12

1 Answer 1


1(a). Yes, in the US, below 18,000 feet and above 3,000 feet, airspace seperation is 500'.

3,000' and above to 18,000 feet: IFR traffic, eastbound fly at odd thousands VFR Traffic, eastbound fly at odd thousands + 500' IFR traffic, westbound fly at even thousands VFR traffic, westbound fly at even thousands + 500'

(I always figured that was because "east is even" would be too easy to remember. JUst like Nav lights, red is in the left because "red on the right" would be too easy to remember. Red/Green is likely a carryover from boating tho.)

1(b), I don't know about Europe.

2 I believe service ceiling is more a factor of jet engine efficiency and aircraft drag. Piston engine's need to be turbocharged or turbonormalized (make sea level power at altitude) to make the high teens need to make air denser for the engine to make power - if you can get up there, the drag drops a lot and you can go a lot faster. Jets are big compressors in essence and can make all the dense air they need to burn jet fuel with.

Why don't more jet arcraft fly higher? Maybe it's not worth it drag reduction-wise, or time savings enroute-wise, to climb higher and then to descend back down.

  • $\begingroup$ Based on the title I believe the first part is talking about RVSM airspace above FL290, so the VFR altitudes wouldn't be relevant. $\endgroup$
    – fooot
    Apr 6, 2018 at 19:21
  • $\begingroup$ Thank you very much for your opinion. So basically this engineer means that engines are changing and speed is increasing therefore drag drops so the only limitationis would be something like in case of cabin depressurizing, it would be much easier to descent to 8000ft from FL320 than from FL420 in certain ammount of time depending on regulation or the oxygen supply. what do you think ? $\endgroup$ Apr 6, 2018 at 19:27
  • $\begingroup$ Or down to FL140 even, plenty of air there (folks hike to the top of Pikes Peak in Colorado all the time, 14,110 feet). I think will still want FL410 for long distance flights for low drag (from the aircraft body, not the engines) and things like ease of maneuvering around summer thunderstorms. $\endgroup$
    – CrossRoads
    Apr 6, 2018 at 19:44
  • $\begingroup$ "East is even" would be too easy to remember, he said sarcastically. For those of us who grew up in the western half of the US, knowing that people from the "East are Odd" was VERY easy to remember, so the mnemonic for that one DID make sense (at least to half of the population). :-D $\endgroup$
    – Jimmy
    Apr 9, 2018 at 7:57

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