NationStates Jolt Archive

I have a question regarding long distance fight for pilots. Please I do not want assumption I want facts. When flying transcontinental over long distances how frequently must you adjust altitude to stay at a specific altitude. Maybe I am wording this the wrong way, let me say this. Lets use sea level as the standard if you wanted to fly at 30,000 ft (?) and stay at that altitude above sea level how frequently would you have to make adjustments to stay at that level?

I have a question regarding long distance fight for pilots. Please I do not want assumption I want facts. When flying transcontinental over long distances how frequently must you adjust altitude to stay at a specific altitude. Maybe I am wording this the wrong way, let me say this. Lets use sea level as the standard if you wanted to fly at 30,000 ft (?) and stay at that altitude above sea level how frequently would you have to make adjustments to stay at that level?
The altimeter depends on the barometric pressure. under 18,000 feet, the pilot must adjust the altimeter every so often to match the correct altitude. over 18,000 however, the altimeter is set to 29.92 inches and stays there, so the pilots can pay attention to more important issues.

Depends on the plane and the weather among other factors. If the plane flies perfectly and doesn't lose altitude due to its design, then it will follow the curve of the earth and maintain its altitude without pilot interference (especially if its on autopilot :D )

Depends on the plane and the weather among other factors. If the plane flies perfectly and doesn't lose altitude due to its design, then it will follow the curve of the earth and maintain its altitude without pilot interference (especially if its on autopilot :D )
ALL planes follow the curve of the earth. No matter what. It doesn't need to follow a perfect flight path. It can change altitude frequently, and still follow the planet curve. This is because there is a special indicator that tells the pilot where the aircraft is oriented. the "Artificial Horizon," it's called.

What Plutonian Empire said. Above the transition layer (18,000 ft in the US, different in other countries or above the ocean) you set the altimeter on 29.92 in, or 1013 mb if it has a metric window, and forget about it.

Below that you have to keep checking back with flight control or flight services or somebody to set the proper pressure. You don't have to do it every five minutes or so, but you're expected to keep it reasonably updated and you must near an airport.

Since not all altimeters will be calibrated the same, and even if they are they may still have errors, you can only fly at altitudes of even or odd thousands (or thousands + 500 ft if flying visual) depending on your direction of flight.

ALL planes follow the curve of the earth. No matter what. It doesn't need to follow a perfect flight path. It can change altitude frequently, and still follow the planet curve. This is because there is a special indicator that tells the pilot where the aircraft is oriented. the "Artificial Horizon," it's called.
Yes but the point is the pilot wouldn't have to DO anything. If planes didn't follow the curve of the earth, we've wasted a lot of money on space programs.

Since altitude is dictated by air traffic control, you would have to fly at whatever altitude they instructed you. To stay at a strict 30,000 feet though, regardless, it would depend upon the terrain. As the altitude of the terrain beneath you rose or fell, you would have to adjust your altitude above sea level.

Since altitude is dictated by air traffic control, you would have to fly at whatever altitude they instructed you. To stay at a strict 30,000 feet though, regardless, it would depend upon the terrain. As the altitude of the terrain beneath you rose or fell, you would have to adjust your altitude above sea level.
In aviation altitude means above sea level. If you want to refer to the distance between the airplane and the ground then you say height. The distance between the ground and sea level is known as elevation.

Above 18,000 ft, flight control will assign you flight levels. So, if they tell you "Ascend and maintain flight level 300" you know it's 30,000 ft in the altimeter and that it's altitude, so it doesn't matter if there are mountains or not. For landing they can say to you "authorized to Niner Thousand Five Hundred" and you know you can descend to 9,500. You would have checked for pressure before that, of course.

Thanks for the info so far. I am not getting the follow the curve of the earth info here. In layman terms are you saying that you can set the control to stay at say 10,000 ft and you will stay there?

Thanks for the info so far. I am not getting the follow the curve of the earth info here. In layman terms are you saying that you can set the control to stay at say 10,000 ft and you will stay there?

Forget about the curve of the earth stuff. That's nonsense. Aircraft fly at altitudes that are determined by atmospheric pressure. Pressure Altitude is adjusted with reference to Mean Sea Level, MSL. The Kohlsmann (sp) windo on the altimeter gives you a place to enter a barometric pressure for a nearby ground station.

If you look at a Surface Analysis map, you will see lines called isobars. These indicate constant pressure. If you look at a chart of the US, you will see that there are a lot of regions where the pressure is different. The problem becomes one of adjusting your altimeter often enough to keep your altitude in sync with other aircraft. Every hundred miles or so is enough. The FAA publication "Airman's Information Manual" specifies how often these updates are required.

So the answer to your question is every hundred miles, if you are trying to maintain a constant pressure altitude.

Thanks for the info so far. I am not getting the follow the curve of the earth info here. In layman terms are you saying that you can set the control to stay at say 10,000 ft and you will stay there?
Yup. You just have to adjust the instrument from time to time to make sure it's not deviating too much from the real altitude.

Don't bother with the curve of the earth, air follows it and so will the plane. Gravity will make sure of that.

Forget about the curve of the earth stuff. That's nonsense. Aircraft fly at altitudes that are determined by atmospheric pressure. Pressure Altitude is adjusted with reference to Mean Sea Level, MSL. The Kohlsmann (sp) windo on the altimeter gives you a place to enter a barometric pressure for a nearby ground station.

If you look at a Surface Analysis map, you will see lines called isobars. These indicate constant pressure. If you look at a chart of the US, you will see that there are a lot of regions where the pressure is different. The problem becomes one of adjusting your altimeter often enough to keep your altitude in sync with other aircraft. Every hundred miles or so is enough. The FAA publication "Airman's Information Manual" specifies how often these updates are required.

So the answer to your question is every hundred miles, if you are trying to maintain a constant pressure altitude.

So, in a 747 with a max cruising speed of approximately 570mph, that would still equate to about once every ten minutes? Or do they have this nicely automated for them?

So, in a 747 with a max cruising speed of approximately 570mph, that would still equate to about once every ten minutes? Or do they have this nicely automated for them?
Nope. The 747 would be flying above 18,000 ft, so they just set the altimeter at 29.92 and forget about it.

um ok....what about turbulace? When you 'can' drop 1000 feet....would your avionics compensate or would have to correct manually in a modern fly by wire airliner?

Here is a strange question. What if you flew to a level of 10k above sea level then rigidly held the plane in a straight line from there? In other words you did not make adjustments for elevation. would you then just continue to ascend upward? Not sure if this is making sense.

um ok....what about turbulace? When you 'can' drop 1000 feet....would your avionics compensate or would have to correct manually in a modern fly by wire airliner?
Most airliners fly above turbulence. However, modern systems can compensate for it, but there would still be variations in altitude. That's another reason to leave some distance between planes and between the plane and the ground.

Here is a strange question. What if you flew to a level of 10k above sea level then rigidly held the plane in a straight line from there? In other words you did not make adjustments for elevation. would you then just continue to ascend upward? Not sure if this is making sense.
No, you would not continue to ascend. Gravity will pull you towards the earth, so you would just keep the same altitude.

Most airliners fly above turbulence. However, modern systems can compensate for it, but there would still be variations in altitude. That's another reason to leave some distance between planes and between the plane and the ground.

hmmm I disagree with you there...

In-flight turbulence is the leading cause of injuries to passengers and crew. Occupants injured during turbulence are usually not wearing seatbelts, ignoring recommendations to keep seatbelts fastened even when the signs are not illuminated. It is recognised that passengers need to move around the cabin to use restroom facilities or to exercise on long flights. However you should keep your seatbelt fastened at all times when seated.

From 1981 through 1997 there were 342 reports of turbulence affecting major air carriers. Three passengers died, two of these fatalities were not wearing their seat belt while the sign was on. 80 suffered serious injuries, 73 of these passengers were also not wearing their seat belts.

http://www.casa.gov.au/airsafe/trip/turbulen.htm

No, you would not continue to ascend. Gravity will pull you towards the earth, so you would just keep the same altitude.

So are you saying that under the above circumstances if you had infinite fuel that once you reached a specific altitude and locked the controls without any adjustments you would fly around the world?

So, in a 747 with a max cruising speed of approximately 570mph, that would still equate to about once every ten minutes? Or do they have this nicely automated for them?
No, this is why flight levels exist. Above 18000 MSL, set 29.92. Below that alitude, yes. But most fast airplanes fly higher.

Most airliners fly above turbulence. However, modern systems can compensate for it, but there would still be variations in altitude. That's another reason to leave some distance between planes and between the plane and the ground.
The techinque recommended for flying through thunderstorms, i.e. maximum turbulence, is to hold attitude, not altitude. Autopilots aren't going to react to momentary turbulence, only to an average. It's a bandwidth thing.

No, you would not continue to ascend. Gravity will pull you towards the earth, so you would just keep the same altitude.
Gravity always pulls you toward the earth. That's not why you don't fly into space, though. In the situation posed, you would be maintaining a constant MSL altitude.

hmmm I disagree with you there...

[i]In-flight turbulence is the leading cause of injuries to passengers and crew. Occupants injured during turbulence are usually not wearing seatbelts, ignoring recommendations to keep seatbelts fastened even when the signs are not illuminated. It is recognised that passengers need to move around the cabin to use restroom facilities or to exercise on long flights. However you should keep your seatbelt fastened at all times when seated.

I agree, that's why I said "most". It's true that sometimes there's turbulence at those altitudes, but it's usually very light and nothing to really worry about. I mean, 342 cases amongst the thousands of flights in those 16 years...

The techinque recommended for flying through thunderstorms, i.e. maximum turbulence, is to hold attitude, not altitude. Autopilots aren't going to react to momentary turbulence, only to an average. It's a bandwidth thing.
Yes. What I meant is that, after the autopilot detects a significant change in altitude, it will take you back to the altitude you preselected. But you're right, that's not the same as reacting or getting ahead of the turbulence.

Gravity always pulls you toward the earth. That's not why you don't fly into space, though. In the situation posed, you would be maintaining a constant MSL altitude.
And you maintain it because the forces acting vertically on the airplane are balanced, and those forces are: sustentation and gravity. And gravity is always directed towards the center of the Earth.

I'm a pilot.
You set it on the ground and it depends on what alt. the runway is.
You change it from time to time in the air so to keep it correct and also if the air traffic controler says that you must.
ICAO reg. don't know if the FAA has it differant. All pilots I know do this and I have never heard of pilots from other nations doing it in other ways.

And you maintain it because the forces acting vertically on the airplane are balanced, and those forces are: sustentation and gravity. And gravity is always directed towards the center of the Earth.
We're splitting hairs. The pilot is making a decision to hold a constant pressure altitude, not a constant gravity setting. The fact the forces and moments sum to zero only allows him to implement his decision.

If you do not have an autopilot, you will have to correct to keep at one altitude since every little thing affects the flight of an airplane, my friend was a commercial pilot and the beech 1900's he flew did not have auto pilots and a passenger moving in the cabin would change the flight of the airplane.
on a long flight, the wieght of the fuel burned will change how the plane flies and have to be corrected for