3
$\begingroup$

How come, for example, the average cruising altitude of let's say the Westjet Boeing 737-600 from CYWG to CYVR flies at an altitude of 38,000 feet-40,000 feet, yet the Air Transat Airbus 330-200 flying from CYVR to Man EGCC flies between 33,000 feet and 35,000 feet? Why is the air transat one flies lower when you'd think that with the Vancouver to Manchester route being more of a long-range flight than the Winnipeg to Vancouver one, it'd want to fly above the regional/domestic flights.

Why is this so? to illustrate, here are flightaware records for two recent flights: Westjet: https://flightaware.com/live/flight/WJA307/history/20150903/1210Z/CYWG/CYVR Air Transat: http://flightaware.com/live/flight/TSC284

$\endgroup$
8
$\begingroup$

It seems you looked at flights which had begun shortly before. Since intercontinental flights require a higher fuel fraction to carry enough fuel for the trip, the airplane cannot climb as high initially as one with little fuel onboard. Note that the maximum range of a Boeing 737-700 is 6230 km, while the flight you chose to take as the basis for your question covered only 1936 km. The tanks were probably less than half full, and depending on the passenger load factor, the airplane was probably well below its maximum take-off mass, hence it had no problem to climb so high early in the flight.

Had you included intercontinental flights close to their destination, your question would had been different. Note that TSC284 flew in FL390 shortly before descending. At this point, the tanks held only a fraction of the fuel at take-off, and for a flight of 7526 km it had probably taken off close to its maximum take-off mass. The fuel load of long-range aircraft like the A330-200 can be more than 40% of the take-off mass, so using up most of the initial fuel load can make a lot of difference in the maximum possible flight altitude.

$\endgroup$
11
$\begingroup$

Flight altitudes have relatively little to do with whether a flight is regional or international per se. More important factors include the winds aloft and the individual aircraft capability.

In the case of the Winnipeg to Manchester flight, they were probably using the North Atlantic Track System (NATS). The winds aloft over the North Atlantic are generally out of the west. The routes of the tracks are arranged each day to take advantage of the those winds. The track system puts the eastbound aircraft on tracks and at altitudes that would maximize the tailwinds, and westbound aircraft on tracks and at altitudes that minimize the headwind.

Since the winds aloft in the northern hemisphere are more often than not westerly, the Winnipeg to Vancouver flight might well have been fighting a headwind, but the strongest winds aloft tend to occur in the mid 30s, which can mean that you can lessen the headwind by climbing higher.

Aircraft capability also plays a major role, and aircraft vary widely in what they can do altitude wise. For example, a 747-200 up against its max takeoff weight of 800,000+ lbs can initially climb to only about 31,000 feet (FL310), but towards the end of the flight can reach FL390 and above.

$\endgroup$
  • $\begingroup$ Would the fact that the Winnipeg to Vancouver flight probibly flies over part of the Rockies play much a roll in the altitude choice too? I know the Vancouver to Manchester does too I believe, the map wouldn't load so I couldn't check. Iknow things get turbulent over mountains, so planes tend to go higher around those areas too. $\endgroup$ – The Cat-alyst Sep 5 '15 at 0:26
  • $\begingroup$ @TheCat-alyst For aircraft with normal cruise altitudes above 30,000 feet, I doubt that the terrain altitude below is itself much of a flight planning consideration, but that's not an area of expertise for me. If you're operating within a few thousand feet of the terrain, certainly it would be. Orthographic lifting, though, dies out fairly quickly as you ascend. However, if that lifting (combined with heat and humidity) causes a thunderstorm, you might say the terrain has been a factor. $\endgroup$ – Terry Sep 5 '15 at 6:31
  • 1
    $\begingroup$ Regional flights are usually much shorter than the range of the aircraft in use, so the performance argument does explain why regional flights typically fly higher. They start lighter, so they can climb to higher altitude straight away. $\endgroup$ – Jan Hudec Sep 5 '15 at 13:47
  • $\begingroup$ If you used typical climb rates how long a ground distance does it take for something like a 747 to reach its max altitude? Do short routes have enough distance to try to climb to their optimal heights & then descend? $\endgroup$ – curious_cat Sep 5 '15 at 18:16
  • 1
    $\begingroup$ @curious_cat You've got two questions there, which I think you should ask as proper questions rather than in a comment. I tried to answer here as a comment, but ran out of room. If you do ask the question about the ground distance, I suggest you use "climb airspeeds" rather than "climb rates" because it's the airspeed rather than the climb rate that is targeted. Also, which max altitude are you referring to? The initial max altitude it's capable of and can go no higher until it burns several thousand pounds of fuel? $\endgroup$ – Terry Sep 6 '15 at 2:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.