Maggot17 - You are officially banned (by me
) from ever asking another pilot a question about anything - Jeezuz mate. Yes it's an important point but I can bet you only know because someone taught you. Same goes for me.
Novicef, as someone else said BENDO got it right.
I'll say it again here, with some further elaboration. There's a lot of words here, but it's really quite simple when the "penny drops"...
NON PRECISION APPROACHES
Three flavours of QNH exist:
1)
Area QNH - available pretty much everywhere all the time.
If you set this, take the "Forecast Terminal QNH" minima from you Jepp plate, or the published minima on your Airservices plate, and add 50'. That's your minima.
2)
Forecast Terminal QNH - available if you have a valid TAF, and your ETA falls within the period covered by the QNH groups at the bottom (NB it may be a TAF with 24 hour validity - that does not mean you have 24 hours of QNH information on the TAF... a minor point but worth knowing).
If you set this, use the "Forecast Terminal QNH" minima from your Jepp plate, or the published minima on your Airservices plate. That's your minima.
3)
Actual Aerodrome QNH - this is the sort you get from an ATIS, AWIB, Tower, approved met. observer etc. In the majority of locations you won't have it. Remember, it is valid only for 15 minutes too. Don't copy the ATIS at 50 miles, bore in, sit in the hold, etc. etc. then fly the approach with a stale QNH, to a reduced minima (not in a renewal anyway
)
If you set this, you can:
(1) For Jepp plates - use the "Actual Aero QNH" minima.
(2) For airservices plates WITH SHADED BOXES - subtract 100' from the printed minima. (If no shading, use the published minima.)
PRECISION APPROACHES
Everything above applies exactly the same, but now...
There is also the question of PEC. This is an instrument
installation correction and not to do with QNH. It is "another" kind of minima "adjustment", and is:
+50 feet, or the published figure from the aircraft's AFM.
With most precision approaches (ie. ILS), you will have access to "Actual Aerodrome QNH" - but there are cases when you won't, and anyway it is important to still understand the theory behind it all.
What a mouthful all that is... But as I said, be not afraid - you will get it with just a little exposure - you probably already have. Sorry if this post came over as patronising. But maybe someone else will read it one day and it will help them to "get it".
CR.