Top Altitudes and ATC

In the United States (and maybe other places) SIDs have published Top Altitudes.

I did a quick search on what they mean, and apparently aircraft aren’t supposed to surpass this altitude until they’ve been permitted by ATC. However, I’ve never heard anybody do this on live, and I’m not sure if the tutorial mentions top altitudes at all (if they do please link them below). I also don’t hear anything concerning the top altitude when I occasionally tune into IRL ATC. I’m sure they do somehow, but I haven’t caught it.

Assuming departure ATC is online, and barring any altitude restrictions on the SID, should I be climbing to the top altitude initially, then requesting a further climb to my cruising altitude?

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Hey there!

When you check in to the Departure frequency in IF, you are automatically granted permission to climb to your initial cruising altitude. Because of that, requesting a higher altitude would be unnecessary.

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Pretty sure standard is not to request a climb in IF.
The only time I request a climb is when I am departing an airport where there are upper restrictions on the STAR (eg. EGLL) and I want to climb ignoring the limot, although even that might not be required in IF.

So, IRL, when we get an IFR clearance on the ground (in the US), part of it goes something like this…

“…on departure, maintain XXXX feet, expect YYYY feet 10 minutes after departure…”

XXXX feet is the initial ‘top altitude’ on the departure, and YYYY feet is a higher (usually your final) cruising altitude.

Now, it would be painful to give these kinds of clearances at very busy airports, where every aircraft is flying one particular departure for each direction. So to standardise and make things more efficient:

"…on departure, maintain XXXX feet,

This part has been charted out in the box, and is called the ‘top altitude.’

Usually though, whenever you check in with Departure, and you’re on a SID, they’ll tell you to ‘climb via the SID,’ or ‘cancel altitude restrictions,’ which then means you can climb unrestricted. If you’re not on a SID, you can expect them to clear you to your final altitude 10 minutes later (or whatever time was specified in the initial clearance).

In IF, I always request an altitude clearance to my cruising level, after I check in with departure. Just to be clear.

Hope that cleared things up!

If you want an even more detailed picture of departure procedures, I suggest this link:


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