Tropopause Height and Optimum Alt in the FMC A320

[VShadow]

Hi Guys,

Sometimes on some flights you will have different tropopause heights on your SIG charts, now entering it into the FMC depending on the weight seems to affect your optimum altitude calculated by the FMC, but how does it behave if your route is crossing different tropopause heights. and how much really does the entering of the tropopause height into the FMC affects performance??

[Henry VIII]

We insert the average.

[waren9]

Pre departure, insert into FMC what it is at top of climb. At top of climb and from then on the FMC I think will use actual encountered conditions throughout the flight for predictions.

I have experienced before where actual SAT was 20degC different from forecast and all of a sudden at top of climb, we got a "ABOVE MAX FL" in the scratchpad.

[BAROREF]

We Had A Tr A Couple Months Ago Saying That You Dont Modify The Default Tropopause Height In The Init A Page Because You Mau Incorrect Info On Rec Max Fl For All Eng And Eng Out,eta And Econ Crz Mach.
It Is For The Fms 2 Thales -smiths Mcdu.

[MyTH]

Before takeoff it's best to insert the tropopause height of the TOC like waren9 said. Updating tropopause values during flight doesn't affect performance that much as long as you have entered correct temperatures on the cruise wind page, which is much more important.

[mcdhu]

The more good info you put into the FMGC, the better the predictions you get out of it! It's as simple as that.

mcdhu