alti settings below transition altitude

[attaltitude]

please coment on this topic on avcom if you have the correct answer under flight safety section thanks

[RV4ker (RIP)]

Local QNH or airfield elevation.... (That why for eg Info will give you the Jhb QNH to ensure you are 7500 or below to remain under the TMA)

[Tumbleweed]

While descending below 1500ft, besides correcting your QNH for your approach altitudes, you're gonna be sharing the airspace with crop sprayers, helis and trikers with possible kak coms so make sure you're on the same altitude.

Adjust your QNH to local altitude + 1500 feet once descending and do an elaborate radio call including your QNH setting and hopefully someone will advise you.

Staying on QNH 1012 where the local is 1030 puts your altitude out by lots and puts you in conflict with everyone who is expecting you at another altitude.

[RV4ker (RIP)]

Think of it the other way round. If you never go above 1500 (or 2000) ft AGL would you change the alti to 1013.2? IMHO Nope. You leave it on last know QNH which is usually when you on the ground with known airfield altitude? Thus the oukes coming from above (flight levels) who have been on 1013.2 need to get onto same qnh as you? Seems logical to me. Can't see why there is such huge debate over the matter?

[Tumbleweed]

Another thing is after flying through or from a different weather pattern your QNH differs from where you now are and suddenly with the congested radio, you're reporting an altitude in conflict with the locals.

[Biggles]

Do the big metal change to local QNH as they descent for approach? Because the base of a TMA is altitude above AMSL. So that is on local QNH and not a FL.

[HansH]

For T/O set local QNH.
When passing the Transition Altitude (TA) change to 1013.2.
On approach with 1013.2 set change to the local QNH when descending through the Transition Level (TL).
The TL is usually 1,000 ft above the TA but can vary in extreme local QNH readings.
The airspace between the TA and the TL is the Transition Layer.
If you reach your TOC and are still below the TA change to 1013.2 when clear of controlled airspace.
On approaching your destination and you are cruising below the TL then change to local QNH as soon as you receive it.