How high you can fly is limited more by your airplane than by anything else. If your airplane can only make FL 310 today (you’re heavy and in a 727, say), then that’s what you file for and what you most likely get. Airplanes capable of higher altitudes will file for and get higher altitudes. On long flights as you burn off fuel and become lighter you can “step-climb” to a higher altitude.
The “restrictions” on airspace only start above FL 600 - and then it reverts to uncontrolled airspace. FL 180-FL600 is normal Class A airspace available for anyone on an IFR flight plan to use.
I know that 757s/767s and 747s can get to FL 410. The 737 is limited to lower altitudes because of it’s wing. Most bizjets now are striving for very long ranges, and they get this by climbing very high. The G-V (Gulfstream Five) can take off at max gross weight and climb directly to FL 500. :eek:
As far maneuvering around thunderstorms and changing altitudes, N9IWP said it best: the pilot is the boss, and ATC (Air Traffic Control) is there to assist. When avoiding thunderstorms, it might go like this:
Airliner 123: “Kansas City Center, Airliner 123 would like deviate 20 degrees left of course for weather”
KCC: “Airliner 123, I have traffic paralleling your course south of you. Unable 20 left at your altitude. Can you accept FL 350?”
Airliner 123: Sounds of buttons being pushed while checking to see if they can climb to 35,000 ft “Center, Airliner 123 is too heavy for FL 350 right now. We can accept either FL 280 or a deviation 20 right.”
KCC: “Roger, Airliner 123. Unable deviation right due to conflicting traffic. You are cleared to descend and maintain FL 280, upon reaching 280 deviation up to 20 degress left of course is approved. Advise when able to accept direct San Simon.”
Airliner 123:“Airliner 123 departing FL 310 for FL 280, will advise.”
So you see, it’s more of a negotiating process. If there is no one else around, whatever deviation you request will get approved right away. Sometimes controllers are proactive and as soon as you check on they tell you “Weather along your route of flight, deviations south (or north, west, whatever) approved.”
Altitude clearances can be flexible as well. Flying a redeye from Seattle-Dallas I’ve been cleared for a “block altitude” - a range of altitudes. We were too heavy to make FL 370, but we could almost get there - so the controller cleared us the block FL 330-FL 370. We just set a slow climb and as the airplane burned off fuel we got higher - reaching FL 370 about an hour later.
What happens when things aren’t so nice and friendly? This quote:
is absolutely not true. The pilot in command has the ultimate authority for safe operation of the airplane. If we see something (weather, another airplane, whatever) that endangers the flight then we have a responsibility to take whatever action necessary to avoid said danger. It’s called exercising your emergency authority.
For example, I have been in situations where we switched over to a new controller, the frequency was extremely busy, and we needed to deviate RIGHT NOW. In that case, you do what you need to (in effect, exercise your emergency authority) to keep the airplane safe, and then advise ATC of what you have done when able. You point the airplane where you need to, and when you can get a word in edgewise you tell ATC what you are doing. Usually it’s no big deal, but sometimes a controller can get in a snit. If you say anything about required maneuvering to maintain safety of flight, they quiet down and get over it.
ATC will also try to talk you into things you don’t want to do, most often a higher or lower altitude. If you can’t do it, you can’t do it.
Upon preview, I see there may be a discussion brewing about ATC/pilot authority. It may be semantics, but here is the way to think about it: ATC is responsible for safe separation of airplanes and traffic flow. The pilot is responsible for safe operation of the airplane. If ATC tells you that you need to do something (fly a new route, descend, whatever) and you can operationally do it, then you must comply. If you can’t comply, let ATC know and something else will be worked out. OTOH, I can request whatever speed and altitude I want, and as long as there is no traffic or other conflict (ie operational ATC issue), then ATC will give me what I request. Both sides say “unable” a lot, but that’s just an operational restriction popping up.
Two different groups, both working toward the same goal.