Polar Route Altitudes

[Ari707]

I've been watching mostly CX flights on Flightaware since I am taking one in Feb and noticed that most have planned altitudes in the 29,000-31,000 range as does CO 99,(ewr-hkg) just wondering why these flights seem to fly at the lower end of the normal altitudes?

[AirtrafficController]

Air Temperature is slightly warmer around those altitudes. Not by much but it can make the difference between a routine flight and an icing problem.

[Matt Molnar]

We asked Twitter. Here are the results... http://storify.com/nycaviation/polar-route-altitudes

[Ari707]

Im going with fuel temps, as we all know what happens to aB777 with frozen fuel...
I will post after my flight to see what altitudes we actually cruise at

[PhilDernerJr]

Also, on those longer routes, they carry so much that their weight prevents them from getting that high. You'd be surprised how altitude-limited even average "heavy" airliners can be.

[CX777]

As Phil mentioned its step climbs, due to ULH sector. I believe the flight aware FPs do not indicate altitude accurately outside States. Last year when I flew on CX841, we took off 31L and after passing Costco headed 360 and came within 90nm of true north pole! Our initial altitude was FL290, then 310, then 330, and somewhere over Mongolia made transition to FL 350 to FL370 and passed 300nm west of Beijing and finally climbed to FL390 till VHHH. I also think over Chinese airspace we flew with metric flight levels.
I will update this with exact FP next week when I fly CX845 to VHHH.

[Ari707]

thanks, I am on CX841 on 2/9 when I get back we can compare notes