hello guys,

 

i know this is stupid and i know im probbal doing something wrong, but i need your help!

 

i planned a flight on pfpx, my units of weights are pounds and cross checked this on the pmdg to make sure were using the same measurements. i finished planning the flight and got a zfw of 135.7 and trip fuel for 10.686lbs. i put all this information into the pmdg and my altudite i was given maximum was FL323. I also cheeked the alt given for cruize from pfpx and it was 360, there is the difference. now if i put fl360 into the fmc i get unable cruise alt.

 

i do not seem to know what i am doing wrong, can i have your help please?

 

many thanks

That's a pretty low zfw and fuel amount. There are only two reasons you would be limited on cruise altitude: 1) too heavy and stall speed gets too close to overspeed, margin of safe flight is not large enough or 2) there's not enough time to reach cruise altitude before TOD. Given that you have such low fuel release for this flight, I'm betting it's the latter and you just have an extremely short flight. I've dealt with similar restrictions recently on short hops between Southern California and Nevada.

i have no idea, that's what pfpx gave so i assumed it was all calculated. hmmm something weird then. ill try to re do the flight plan and see if i can get a different result.

I'd double check your entry in the PMDG. Make sure the airplane is setup to take pounds instead of kgs. That is about 5% fuel of the total you can put in, and 25% of the weight. Your cruising altitude should be over FL390 for a short empty flight.

i have no idea, that's what pfpx gave so i assumed it was all calculated. hmmm something weird then. ill try to re do the flight plan and see if i can get a different result.

You haven't mentioned the departure or arrival airports. Your flight plan is probably too short to reach FL360 before having to descend. Forget about PFPX in this instance. Trust the FMC, and cut the cruise altitude at FL320. Your cruise alt is not limited by weight, but the time and distance you have during the flight, which must be a tiny hop based on your fuel numbers.