Altimeter Setting at 17000-18000' block

tbstanto

tbstanto

Well-Known Member
I was flying today and talking with the good folks at XXXXX Center. An airplane was assigned to FL220, and center contacted them and asked them to check their altimeter's barometric pressure setting, as they appeared to be 300' too high. As expected, they had forgotten to set their altimeter to 29.92. No harm, no one yelled or screamed or anything, someone was just a little embarrassed.

A few minutes later, XXXXX Center came back on and asked the offending aircraft if they had a minute, as they had a question that they did not know the answer to. "What pressure setting would you use if assigned a block altitude from 17,000' to 18,000' ?" Evidently they asked everyone in the Center, including their supervisors, and no one knew.

Several people responded on the frequency, and no one knew for sure what the correct answer was. The best guess is that they should use local pressure below 17,999 and change it to 29.92 once crossing 18,000'. By that point, however, the airplane would no longer be at 18,000' indicated.

Any thoughts on this? Personally, I think that I would ask Center what pressure they wanted me to use. As long as we are both on the same page, that seems like the best solution to me.
 
Up to 17,999 I'd use local.


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If cleared for a block one seven thousand to one eight thousand, use the qnh all the way up to and including 18000. It does not become 29.92 until a controller uses the term "flight level 1 8 0". I have actually been assigned 18000, and fl180, the difference in altimeter setting comes from the difference in name. Dumb question IMHO, from that controller.
 
§ 91.121 Altimeter settings.
(a) Each person operating an aircraft shall maintain the cruising altitude or flight level of that aircraft, as the case may be, by reference to an altimeter that is set, when operating—

(1) Below 18,000 feet MSL, to—

(i) The current reported altimeter setting of a station along the route and within 100 nautical miles of the aircraft;​

(2) At or above 18,000 feet MSL, to 29.92″ Hg.

(b) The lowest usable flight level is determined by the atmospheric pressure in the area of operation as shown in the following table [omitted for blueberry]​
 
Ziggyfuzz said:
If cleared for a block one seven thousand to one eight thousand, use the qnh all the way up to and including 18000. It does not become 29.92 until a controller uses the term "flight level 1 8 0". I have actually been assigned 18000, and fl180, the difference in altimeter setting comes from the difference in name. Dumb question IMHO, from that controller.
Click to expand...

Personally, I think that's pretty dumb to assign 18,000. I don't know why anyone would assign you 18,000 in the US. There is no logical explanation other than the controller just had a brain fart.
 
There's no such thing in the US as "18,000 feet" as an assigned altitude, unless you are in Special Use Airspace, in which case there are other specific rules for what altimeter setting to use when in it.
 
FL180 is very often unusable. If we want it we ask for the 17k-fl190 block. 29.92 at 18k.

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