PPRuNe Forums - View Single Post - altimeter setting
View Single Post
Old 20th Dec 2016, 00:32
  #21 (permalink)  
Derfred
 
Join Date: Jun 2006
Location: Brisbane
Posts: 265
Likes: 0
Received 0 Likes on 0 Posts
Yes, but your FMC is basing it's altitude restrictions on your primary altimeters (assuming you have an FMC).

So if on departure, say TA is 10,000', you have a SID with an "at or above 8000" at a waypoint, and your clearance is to climb to FL140.

I have trouble with how the FMC (or you for that matter) complies with the "at or above 8000" if you have already selected the primary altimeter reference to STD prior to passing 8000'.

There is in fact a STAR in YBBN that has a limiting* descent restriction of "at or below FL120" with a TL of FL110. Your typical clearance at this point is to descend to 9000'. This can really catch you out if you go to QNH early.

*I use the term "limiting" here to indicate that (depending on runway) this waypoint is below the normal descent profile so is the "controlling" waypoint for the descent, meaning correct altimetry at this waypoint is vital.
Derfred is offline