Piloting an airliner: How high? How much pilot discretion?

On a recent flight, the pilot told us we were flying at 41,000 feet. My understanding has always been that altititudes above 40,000 are “controlled by the military” and generally off-limits to commercial airliners, unless special permission (e.g. Concorde) is granted.

What is the general rule re: altitude restrictions? And, though a lot of this might be limited by fuel comsumption, about how high can a commercial airliner theoretically fly? How high do corporate jets fly?

A last question: how much discretion do airliner pilots have in negotiating around, say, thunderheads, etc.? Must they get permission from ground control or are they told to maintain a specific altitude and direction, but have authority to steer away from nasty thunderstorm cells?

Most common jet airliners have a service ceiling in the 30’s. For instance, the service ceiling for a 737 is 35,000 feet and it is 36,000 feet for a 777. This is the highest altitude that they can normally fly due to aerodynamics. However, some corporate jets can fly much higher. A lear jet for instance, has a service ceiling of 51,000 feet. I am not sure what type of plane you flew on that could fly up to 41,000 feet.

Jet airliners are almost always controlled by air traffic control. The routes and altitude of flight are determined by ATC.
The pilot has no discretion to maneuver unless directed by ATC. However, a pilot may request vectors around nasty weather if he feels it would be prudent and it is up to ATC to decide if and how to do it. This is referred to as Instrument Flight Rules (IFR). Smaller aircraft like Cessnas flown for leisure may opt to fly under Visual Flight Rules (VFR). VFR flight allows the pilot to manuever at will under most airspace and requires that the pilot watch out for traffic and to stay out of clouds and nasty weather.

Technically the Pilot is boss and it is ATCs responsibility to assist. (at least that is my undestaning, I’m a mere VFR pilot)
Now a pilot may request an altitude and be denied because there is traffic already at that altitude.

Class A airspace (need to be under IFR unless a waiver is granted) startes at 18,000 feet and goes to 60,000 feet MSL.
I’ve never heard of the 40,000 foot rule, but then again I’ve never flown at above 6,000 ft MSL.


I know I’ve been on a 747 at 41k. No higher, that I know of.

Do recall the pilots saying on various occasions that they’d “gotten permission to move down a few thousand feet to try and get a smoother ride.”

Obviously the pilot also has to have some discretion to deal with true emergencies.

A 747 has a service ceiling of 45,000 feet so that is indeed possible. It could be the aircraft that the OP was referencing also.

I disagree that ATC is merely there to assist in IFR flight. It may simply be a matter of semantics but the pilot is there to fly the plane and follow ATC instructions for heading, altitude, and even speed (at certain points in flight). The pilot cannot maneuver at all without direction from ATC except in cases of emergency.

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.

A very good answer by pilot141.

I’ll add that I’ve never heard of or seen anything in the FARs relating to military control of airspace above FL400. Military aircraft may use such airspace, but when they are outside airspace for which they have a blanket clearance (e.g., a Restricted area), they must talk to ATC as a civilian aircraft would.

(Obviously, this would be different in wartime, or in a case like the days that followed 9/11).

I don’t have much to add that pilot141 didn’t, except to chime in that maybe apart from some restricted airspaces or military training routes, there are no “blanket controls” on airspace above a certain altitude. Military aircraft are more likely to operate above commercial/civilian aircraft but there are (to my knowledge) no restrictions on aircraft operating at that altitude.

Those who are saying “the pilot is boss” are correct; it is ATC’s job to expedite smooth traffic flow, not fly each aircraft individually. In case of bad weather, they have to defer some control to the pilots because (again, to my knowledge) clouds do not show up on air traffic radar[sup]*[/sup]. The amount of control they relinquish is dependent on other traffic, as pilot141 described.

[sup]*- Though, if I’m wrong about this, I invite someone to correct me… [/sup]

Just to clarify, for those of you confused by “FL 400”, for example, just tack two zeroes on the end of the number and that’s the altitude. FL 400 is 40,000 feet.

InfoThe altimeters that airplanes use are basically fancy barometers. There is a dial one uses to set the local air pressure. (Or you turn it so your altitude matches what you know you are at on the ground).

At the speeds modern jets travel at teh loacl air pressure changes a lot. So at 18,000 ft and above everyone just uses 29.92 inHg as the local air pressure. So FL300 is only 30,000 ft if the local air pressure is 29.92


av8rmike ATC radar has much better weather depiction now than it did just a few years ago. Clouds don’t show up, but precipitation does. This gives the controllers a better idea of what the airplanes are dealing with, and can help them when offering deviations.

Well, it’s Class E, so it is controlled airspace. Sorry, I don’t mean to nitpick, I know you chose your words for the non-pilot crowd. :slight_smile:

No sweat - thanks for keeping me honest! It’s always a fine line to walk, and I hope that most non-pilots can understand my ramblings. :wink:

Thank you! Great information, everyone.

During an emergency, you can do anything you want.
If you live, you might be asked to explain… Bawahahahaha

Been there, done that… Was not fun.