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Thread: Altimeter transition altitude

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    Altimeter transition altitude

    Unless we frag a 'force QNH', we switch to 29.92 at FL180 even in the NTTR as we're in US airspace.

    Hypothetical, at a given day standard setting will read 1,540ft at the Nellis RWY 03 threshold so we adjust our altimeter to read 1,840ft at the 03 threshold (or S-E EOR for that matter).

    If FL180 is the transition altitude and I switch to standard upon reaching it, I have only 200ft seperation with somebody who hasn't transitioned yet and is flying at 17,500ft. Is there something like a minimum altitude above FL180 you have to fly in order to ensure vertical deconfliction? Or is that something we should frag and adjust to on a case-by-case basis?

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    Quote Originally Posted by Oliver View Post
    we switch to 29.92 at FL180 even in the NTTR as we're in US airspace.
    Within the confines of NTTR use the Nellis AFB altimeter setting at all altitudes.

    Providing CAS when you're all out of HUA!

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    Right, missed that one. Thought that was the case when explicitly fragged to froce QNH.

    However, still a valid question regardless of the local procedure I guess.

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    You wouldn't typically fly at the transition level, specifically to ensure safe separation. Equally you wouldn't fly just below transition altitude either.

    Although this is the kind of thing ATC would handle by assigning altitudes to traffic under their control. Part of the reason for force QNH useage is to allow safe separation under tactical conditions where aircraft aren't just cruising at set altitudes under ATC control.

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    There is also something called minimum usable flight level, which prevents such conflicts between aircraft using local altimeter setting and aircraft using standard altimeter setting. Essentially it ensures adequate separation between the two by having aircraft on the standard altimeter setting fly no lower than FL190 or FL200 depending on how low the local altimeter setting is.

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    Alright, so in the event we'll fly at Angels 18,000 or higher (F-5E and Hornet, if I'm still physically able to sim by then) outside of the NTTR it's a matter of briefing the above.

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    In those kind of jets you'd be well above FL180 anyway.

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    Quote Originally Posted by Oliver View Post
    Hypothetical, at a given day standard setting will read 1,540ft at the Nellis RWY 03 threshold so we adjust our altimeter to read 1,840ft at the 03 threshold (or S-E EOR for that matter).
    Before we had a WX brief, this was the technique for deriving your own altimeter setting. Now that we have official WX, real world we would set the provided altimeter setting and verify that it reads within +/- 75 feet of 1840 in the EOR. If it didn't, real world you have a bad altimeter. DCS, since our altimeters don't go bad, you likely just copied it down wrong off the sheet. Ultimately in DCS both will get you there but only because it's a controlled sim.

    As for transition altitudes and settings, some of this has been discussed before here and here. As for lowest usuable flight levels, yeah that's a thing but I think an unnecessary one for the 476 in DCS. If folks are really concerned that it may cause a conflict, then we can set a standard minimum FL outside NTTR that covers all cases but I think the odds you have a conflict because of this are so small it's not worth bothering with it.
    “Rules are made for people who aren't willing to make up their own. " - Chuck Yeager

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    GOMER 2 Noodle's Avatar
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    Quote Originally Posted by Tex View Post
    As for transition altitudes and settings, some of this has been discussed before here.
    Good Lawd, that's a sexy thread!

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    Noodle, again, great work on that altimeter discussion and bullet points.

    From what I understand, unless you're doing ferry flights in the Hog, I highly doubt you will ever cross the transition level. It also depends on the country you're in. I m hazarding a guess here but some places in Europe its 5,000 feet. A lot of is M.E.A. , or Minimum En-route Altitude, derived, and somewhere like the UK you wont really have to worry about straying into the cumulo-granite clouds (mountains). However, here in the States, lots of higher M.E.A.s up into the 15-16 ranges, sometimes even higher. So, 18,000 was set for the United States.

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