Yesterday I was flying DEN to ORD on UAL1220 (757) FL 370, listening to Channel 9. ATC requested that we climb to FL 390 for traffic. The pilot responded that he would prefer not to. My question is, why? My first thought was that fuel expense for the climb would be greater than fuel saved by flying a higher FL. Is this the reason?
What’s the service ceiling on a 757? I know I’ve been to FL410 on a 767, can the 757 go that high too?
PS, I don’t recall ever seeing a 757 above FL370 here on FA…
maybe the plane was too heavy
Could be 1 of a million reasons . . . I’ve been on a 757 at FL380, so they can go above 370 . . . But since it’s fun to speculate . . .
Could be weight, but it’s a relatively short flight for a 757, but maybe the cargo hold is full of bricks, so they were too heavy to go higher
Maybe there was a limit on this particular aircraft’s cabin altitude for some reason, so FL370 was as high as they could go to maintain the maximum cabin altitude.
Maybe it was nice and smooth at FL370, and they didn’t want to leave.
Maybe the best tailwind factor was at FL370.
Maybe the captain was in a bad mood and didn’t want to help out ATC separate traffic that day.
Reminds me of the classic joke:
Center: “United 1220, climb and maintain FL390”
Pilot: “We’d like to stay at FL370”
Center: “Roger, we’ll do it the hard way . . . NWA436, turn left 10 degrees, COA175, reduce speed to mach.74, SKW6542, fly heading 240. . .”
…maybe the pilot hates management so much, that he refuses to do anything to help the airline. 
I don’t think there would be a limit on the cabin altitude.
All pressurized airplanes have a maximum pressure differential . . . when you reach it, the only way to climb is to raise the cabin pressure (or let the airplane break apart). I suppose, technically, the limit of the cabin pressure could be the actual altitude the airplane is at, but at FL370, everyone on board would be dead.
My point was that I once had a J328 at my airport that was restricted to a cabin altitude of 3000’ due to some sort of medical issue of a passenger (SYX from ATW-MKE, 15 min flight). I think the flight only went to 9000’, so it wouldn’t have mattered, but the crew thought it was pertinent info to tell ATC anyway.
So what I was saying was that if there was a reason that the airplane was restricted to a cabin pressure of say 8000’ (maybe a lifeguard flight, UAL does lifeguard flights sometimes), perhaps that would limit them to FL370. I don’t know the real numbers.
It could be. Did you ask the pilot after the flight?
420
Service Ceiling for the 757 is FL420. The maximum Cabin Pressurization Differential (psid) is 8.9, which yields about a 7,500’ cabin altitude at FL420. Probably not a pressurization issue or it wouldn’t have even departed. Safety…
Probably not a it takes too much fuel to climb issue… Jet engines are more fuel efficient the higher the altitude. And the 2000’ climb burn would be minimal compared to the lower, more efficient overall burn at FL390.
More than likely it was a weight limitation. The 757’s optimal altitude for a weight of 190,000 lbs. is FL370. It’s max allowable weight for that altitude is about 205,000 lbs. Max take-off weight is about 240,000 lbs. So if it was full of peeps, bags, mail, and cargo…a weight of 190,000 to 200,000 lbs. is a likely scenario, especially on a DEN-ORD run.
Just my semi-educated opinion…
If its a shorter flight the pilot could have just decided that it wasn’t worth it. NW has a flight from DTW-FNT that’s supposedly 35 minutes long. But from what I heard from their pilots as soon as they get to altitude they start landing.
it’s quite comon for them to go above 370. Out here it is anyways.
It’s a simple question of weight ratios. A five ounce bird can NOT carry a one pound coconut.
I think this is a very simple question to answer, sure they might burn less fuel at a higher altitude, but it’ll probably take them longer. The higher you go above your best altitude the slower true airspeed you’ll be able to get. On a long flight a change of 2000 ft with the subsequent lower speed and possibly increased headwind might be anywhere from 5 to 15 minutes longer.
In the Pilatus our fastest altitudes where between FL200 and FL240, but on long flight we had no choice but to go higher and take the longer enroute times to save fuel.
In the Piaggio we’re fastest at about FL320, but we’ll go higher on long flights, and even higher on empty legs to save the fuel burn. The extra time on the airframe is made up for by saving fuel.
AZ, one more post, man, one more post.
-J-
No! Leave it like that! Make a new account! 
I meant that the plane wouldn’t have a problem flying at 39,000 feet.
A helpful moderator could lock it!
Maybe the airlines procedure is to try and stay as close to optimum altitude as possible and 370 was the optimum or very near.
just a thought
It could be carried by an African swallow!
Yes but what about two birds working in concert, they could easily spread the weight?
MUST…RESIST…ADDING…MOVIE…QUOTES…
Anyway, can you believe that someone actually had this much fun with that part of the movie…
BTW, on that flight UAL was “testing” a new idea. You could buy a candy bar or a pack of Twizzlers for 3 bucks.
Since the POLAR2 approach to DTW comes very close to basically overflying FNT, they simply climb enough to match the next crossing altitude on the STAR.