A320 flex temperature discrepancy upon take off

[MrFly]

I have noticed in a very few occasions that the flex temperature fed into the FMGC and temperature shown in the EWD during the T.O. run differ in one degree.
Why does this happen? Is the system making any correction of the sensed OAT in that moment? Or is just a matter of rounding off numbers in some mysterious internal calculations??

[Superpilot]

Good question. I've seen a similar thing related to another parameter (can't exactly recall right now). I.e. the source for the data, according to the books, is the same but you get slightly different numbers depending on the screen you're looking at. My guess is that the DMCs perform their own rounding up/down on individual values before displaying rather than just streaming the values directly from the FMGS. Though I could be wrong on this.

[Superpilot]

That's it, I remember now... You get the same tiny discrepency sometimes when looking at a waypoint ETA on the MCDU and comparing it with the ETA value shown in the top corner of the onside ND.

[DEVILFISH]

Two different ways of calculating.
One is predicting ( ie wind inserted), the other is actual ( ie wind detected)

[Superpilot]

Now that's true

[Metro man]

CFM or IAE engines ?

[MD83FO]

MCDU prediction is using MCDU wind, ND prediction is using ND wind.

[CONF iture]

Originally Posted by MD83FO

MCDU prediction is using MCDU wind, ND prediction is using ND wind.

Originally Posted by DEVILFISH

Two different ways of calculating.
One is predicting ( ie wind inserted), the other is actual ( ie wind detected)

The reason is different : ND prediction is strictly using the actual ground speed.

[lurkio]

MrFly, the figures entered by you into the FMGC are sent to the EIU & FADEC as N1 targets. FADEC then computes an N1 limit from its own sensors of ambient which it then displays on the E/WD. This would account for small differences and hopefully the E/WD figures is a lesser temp than the FMGC. You can put something absurd (say 85 degrees) in the FMGC and hopefully FADEC would only compute and display the max allowable under regulation. If you do please reset it as I dont want to read about it in R & N.