FLEX N1 Rating lower than CLB N1 rating

[geckuz]

Good day,

as per object, N1 for FLEX takeoff is wrongly implemented. A320 FADEC does not allow the FLEX N1 to be lower than the CLB N1.

In general, it looks like N1 rating in FLEX is low.

With FLEX TEMP of 54 I got 76% N1 on FLX and 85% as soon as I moved to CLB.

 CAn you look into this?

[richboy2307]

Hi @geckuz

Thanks for your post.

On 6/2/2024 at 5:10 AM, geckuz said:

A320 FADEC does not allow the FLEX N1 to be lower than the CLB N1.

Unfortunately this is not correct, and a misconception derived from an old version of FCOM. Such a limitation was only applicable to very early variants of the A320ceo.

The A320neo meanwhile is a different beast altogether when it comes to Flexible Thrust takeoffs when compared to any variant of the A320ceo. The A320neo engines generally have more FLEX by comparison. 

Here is a real world example of an A320neo where the FLEX N1% target (~79%) is lower than the CLB one (~83%).
https://youtu.be/cv41hm4JEB8?t=157

And also for A321ceo where the FLEX N1% target (~85%) is lower than the CLB one (~87%).
 https://youtu.be/LGeegwNsKwU?si=Iir3j35AKEqxTQxt&t=1120

On 6/2/2024 at 5:10 AM, geckuz said:

 CAn you look into this?

We are looking into improvements for calculations at high altitudes in a future update, but generally, performance calculations are a complex subject with a lot of variables at play.

The takeoff speeds are optimised for maximum flex for the given restriction, meaning on a dry runway 50ft elevation at the end of it, and 35ft for a wet one. The EFB's computed performance is aiming to FLEX as much as possible while giving as much climb gradient for the 2nd segment which is often why you see 2nd segment limited message, and it will try to use up as much runway as it can if it means it can flex the engines more.

Thanks!