What like how big you can fit in there?

www.airnav.com It has maximum runway weight limits, only covers the US I think though.

Ditto Saratoga's recommendation- Airnav is a great site.
  Reminds me that I've noticed that in FS9, ATC seems to not know what airspace is what- got a clearance to" transition the Class Delta" airspace over JFK recently, when in reality the combined airspaces of JFK, LGA, and EWR are definitely Class Bravo.
By law, you don't even need a clearance to enter a Class D, just have to establish comm. They can ask you to stay out, but unless you're landing or passing through under IFR, you're not under their control.

Quote:

.....you may be mincing terms and requirements but aircraft class....A,B,C,D...with relation to approach speed is listed on ANY Jeppesen approach plate:
class A-90kias MAX/class B-120kias MAX/class C-140kias MAX and class D-165kias
Usually you would use 1.2xVso to find your airplane's approach speed.  The airport itself doesn't list these numbers but may limit a certain class(due to speed or terrain limitations). The class only affects the approach itself, specifically ceiling and visibility requirements.
The only limiting factor for an airport itself is usually gross weight and landing gear width.

I could be wrong so take this with a grain of salt, but I don't know of any "Classifications" for aircrafts or runways in the US.

the runways are designed to sustain a certain weight for the plane. That plus their lenght, in conjuction with the aircraft performance, allows you (the Pilot in Command) to decide if your plane can land on a runway or not.

it's entirely up to you. If you want to try to land a 747 on a turf 3000 foot runway and you manage to walk away from it on your own legs, kudos to you.

It's literally decided based on the runway and plane.

The plane's performance determines the minimum runway lenght. The runway's surface determines the max plane's weight.

Those two things togheter tell you where you can or cannot land, safely.

Airnav is what I use to decide where I can land my plane usually ... not that there's that many places I wouldn't be able to land my plane at ...

That's all i know ... and again, I may be wrong.

Maybe there are differrent rules in specific areas then. I talked to a friend who has the Private Pilot Certification. From what he told me a tower on an airport with a 4000ft runway would not give clearance for landing to a 747 (for example) unless under emergency situation but as I said he is only PP not a commercial pilot. He was talking about the Greek FIR though.

You need to be in contact with someone (or have prior arrangements if no radio is available) to fly through it. For all airspace. Though most you can sneak under if you are a GA plane.