Who's Online

We have 1604 guests online

Live Traffic Feed

Life in the Skies

'A Local Bestseller!'

What Tony says
(See here)
and Book Launch video here
What others say

Les Posen

Yvonne Lee

Louisa Lim & Allan Koay

Aireen Omar, Asran & Bo Lingam

38 Readers' Comments
(See here)

Get an autographed copy here

AMAZON.COM  -  To Order, please Click here 

(eBook) Kindle edition - please Click here

Latest Comment

Do airplanes now fly
I totally agree. Of course, the causes of vanishi

What are the eyesigh
my one eye is infected by glaucoma i m intrested

Can I become an airl
What is the minimum height requireed to become a p

Could the Boeing 777
Yes. Ground speed (GS) and Airspeed (AS) are very

Was the computer fly
That's cool

Pilot aspirant - Sho
Totally agree with Captain Lim.

Changing my career f
Hi Captain Lim, Please could you interpret a ridd

What happens when al
Hi, can I ask in the case of loss of both engines

Do airplanes now fly
I totally agree. Of course, the causes of vanishi

Avianca Flight 52: W
"Priority" was not mentioned until two of the engi

Paperback Version

 For Local Availability - Check Here
Home > Air Safety > What limits a plane to fly higher than the normal cruising altitude?
What limits a plane to fly higher than the normal cruising altitude?
Aviation - Air Safety
Monday, 21 August 2006 10:01

Dear Captain Lim,

This is great site with very interesting topics. I enjoy reading it very much.

Well, Captain, maybe this is a silly question, but let*s start with this statement: No oxygen, no fire. Right?

If there is very little oxygen at 10 000 meters (35000 feet), can a turbine engine burn fuel with the same efficiency as it would during take-off or at lower altitudes?

And what limits a plane to fly higher than the normal cruising altitude?
I haven*t had the time to go through all the topics yet, maybe these questions have been asked before.

Kindly refer me to where this has been discussed on your site.


Marc Vancamelbeke

Hi Marc,

It is true that the amount of oxygen decreases (to support the combustion) in a jet engine as altitude increases. Yes, they are unlike rockets that carry their own source of oxygen instead of getting them from the air. However, there are other factors that make the jet engine more efficient at a higher cruising altitude when compared to the turbo-prop (propellers) engines.

At higher altitude, the temperature decreases. The colder the air temperature, the better it is for the jet engine as it convert fuel more efficiently at low outside air temperatures. Basically, the efficiency is directly proportional to the temperature differential. The greater that temperature differential is, the more efficient the engine.

Colder air is also good for jet engine operation. Colder mass means more air. Remember the principle of a gas turbine engine - it requires air to be sucked at the front, compressed, combusted then expanded and blasted out through the jet nozzle (a more simplistic explanation - suck, squeeze, blow and go!)

Further, when a plane climb higher, the air outside gets thinner and less dense. This has the effect of reducing the forward resistance.

So, overall, a gas turbine engine is more fuel efficient when operated at higher altitudes than nearer to the surface.

Now that I have explained why it is more efficient for a plane to fly at a higher cruising altitude, what then limits a plane to fly higher than this normal cruising altitude?

On a Boeing 777, the maximum service ceiling (altitude at which the maximum rate of climb is reduced to around 100 feet/min) or aircraft*s certification altitude is 43,100 feet. But, most of the time, the plane cruises at its optimum altitude of between 35,000 to 39,000 feet (this depends mainly on the weight and the environmental conditions.) If the flight were on a 12-hour journey with a full load where it would take off near to its maximum take off weight (approximately 286 tons), then it could only cruise initially at around 29,000 feet.

What other factors that limit the height? Cabin pressure differential is one. All airplanes are pressurized to maintain a comfortable living environment for human beings. Off course, if it were possible, a plane would be pressurized to ground level pressure but this is not practical, as the fuselage of a plane would have to be incredibly strong. Therefore, modern airliners are only pressurized to an altitude of around 8000 feet or a cabin pressure differential of 8.5 psi (pounds per square inch). Yes, at 43,000 feet actual cruising altitude on the Boeing 777, you are only experiencing an altitude of only 8000 feet in the passenger cabin!

Then there are the technical performance limitations - mostly the wing area and engine thrust available of the particular plane. On a Boeing 747-400, the maximum ceiling is 45,000 feet and on the Airbus A320, it is 39,800 feet. So, it varies with the different type of planes concerned. Generally, most airliners could fly at higher altitudes, but they are usually certified to an altitude that gives them a good safety margin.


TrackBack URI for this entry

Comments (2)

Subscribe to this comment's feed
High altitude
I'm doing this homework for school and I'm getting confused with why planes fly at high altitude.
PLEASE HELP!!!!!!!!!!!!
katie , 18 Jan, 2013
Please answer a question about East-West flight
Hello Capt. Lim,
Please help me understand. Let's say I'm taking a trip to Hawaii. I board a non-stop flight at LAX. Of the three airlines that I checked, they all had an average of 5 hrs 35 min for this flight with only about 10 minutes variation between them. I checked Delta, Hawaiian and United.

I have a great vacation then have to head back to LAX. Again, I catch the non-stop. Now, I've read that the Earth spins at 1000 miles per hour which gives us a full night/day cycle every 24 hours because the circumference of the Earth at the Equator is 24,902 miles according to numerous online sources.

That makes me wonder why the return non-stop is 5 hrs 20 minutes with only a 10 min variation. It would appear to me that one of these flights should be considerably shorter since the Earth is bringing the destination to you at 1000 per hour.

Please help me understand this. Thanks a lot!

Patricia , 22 Mar, 2015

Write comment

smaller | bigger


Paperback Version

 For Local Availability - Check Here

Recommended By..


'A Local Bestseller!'

Recommended by

Patrick Smith
Boston USA

Capt Meryl Getline
ex-United Airlines USA

Capt Doug Morris
Canadian Airlines

Capt  Robert J Boser
ex-United Airlines USA

38 Readers' Comments
(See here)

Get an autographed copy here

AMAZON.COM  -  To Order, please Click here 

(eBook) Kindle edition - please Click here

View Book Launch video here

Follow me


Like What You Read?

If you like what you read, more stories are found in my book LIFE IN THE SKIES (Preview here) and you can purchase a copy here. To check for any latest updates or postings, you can follow my Twitter at @CaptKHLim or Facebook here

MH 370 Interviews

Click here to View

10 Most Popular Posts

30 Previous Posts

Disclaimer | Privacy
2004 - 2011 © AskCaptainLim.com | Site Concept by eQuilec.com