MMMX

[Toga]

I've tried a few approaches and departures using +40 C OAT and 360 Tonne TOW and don't seem to have many problems. Is this not a little unusual? The density alt at over 40 degrees would surely limit the aircraft's performance and MTOW more than i'm seeing in PSX? Maybe not. Anyone care to add?

Toga

[Hardy Heinlin]

No.

You may also consider checking your weather design. It's possible to set 50°C at La Paz at 13000 ft. But such a setting is rather experimental than realistic.

[Toga]

Thanks Hardy. Yes it's a tad unrealistic I just wanted to see what the outcome would be.
Am I correct in thinking BA restrict their MTOW to < 310 T at MMMX?

[Jeroen D]

The density alt at over 40 degrees would surely limit the aircraft's performance and MTOW more than i'm seeing in PSX? Maybe not. Anyone care to add?

MTOW is a number you calculate as part of your pre-flight. I'm not sure PSX or the FMC rather, does anything with the number of such. It just uses the TOW you input.

Not sure which parts of the performance you are looking at. But at heavy weights high density altitude you will surely see a longer take off roll. Have you tried accelerating to V1 and then slam the brakes on? Will you overrun the end of the runway?

Jeroen

[Britjet]

The highest TOPL that you can obtain with nil wind and an OAT of +40C would be on 05R which would be 302 Tonnes.
(Source BA take-off performance)..
Peter.

[Toga]

Thanks Peter. I'm assuming that no assumed temp is used at MMMX? Using Gary's card i get:

message:NOTES
See Performance Restrictions
Page MEX/00A

Not sure where I would find such information, I'm assuming it's not readily available.

[Hardy Heinlin]

Also don't forget the max allowed tire speed. If your VR is near 170 KIAS at 7300 ft, 40°C, 360 tons, your groundspeed exceeds 200 kt (with no wind).

And don't forget that you need enough climb power in case of engine failures.

[Britjet]

Hi Toga,

The ground staff would be given a TOPL to work to on a general basis to ensure they don't overload the aircraft with freight etc before the final TOPL is calculated on the day.
A typical evening temp of, say 18C would probably give you something in the region of 340T. (You would typically gain about a tonne for every 1 degree C temp reduction). There is also a "trick" of deliberately loading the aircraft to give an aft CG, typically aft of 21%, which reduces required stabilizer download, and this will give you about another 2 tonnes.
There are various engine-out scenarios as well, including engine-out SIDs, so the climbout is also critical.
HTH
Peter.

[Jeroen Hoppenbrouwers]

So, as in most things aviation, everything will look nice and cozy at takeoff with plenty of room to spare, and then *poof* something breaks and suddenly you find yourself just above the danger zone -- by design ABOVE.

If the airplane already struggles at normal takeoff ... argh ...


H

[Toga]

Thanks for the insights chaps. Much appreciated!

[Gary Oliver]

Thanks Peter. I'm assuming that no assumed temp is used at MMMX? Using Gary's card i get:

message:NOTES
See Performance Restrictions
Page MEX/00A

Not sure where I would find such information, I'm assuming it's not readily available.

I tried this on my phone when I saw the post, I'll take a look as to why we can't calculate any card for MMMX