N1 D-TOGA THRUST

[dr_anthony]

Noticed that N1 derated thrust can't be dropped below 84,9 value, not in auto N1 mode, nor in manual n1 bug mode. Noticed it in winter flight, then d-to values really low.

We believe FCOM:

It means, that -20 OAT we can reduced TO thrust to 25 % - 84,8 - 25 % = 63,6 N1 

And it means, that -40 OAT shouldn't  be  more than 81,4 - 82,1 in UNEE (880 AGL), but we can see this:

And -50 OAT not more than 79,6

In high ambient temp and N1 higher 84,8 all works fine.

That should be correct. Thanks.

[Litjan]

No. 25% less thrust is not N1 - 25. Thrust does not relate to N1 in a linear way.

 

[dr_anthony]

40 minutes ago, Litjan said:

No. 25% less thrust is not N1 - 25. Thrust does not relate to N1 in a linear way.

 

Its correct. Thrust depend on OAT and pressure on tkf field (feet AGL).  

But it shouldn't exceed maximum values of 81,4 at -40 Cel OAT 0 AGL and 79,6 at -50 OAT 0 AGL all the way, isn't it?

In IXEG FMC logic derates of TO thrust relate to N1 values linear: 106 N1 max - 25 % - 84,8 N1 min. 

Or in this conditions - below -40 Cel OAT needs to use manual takeoff thrust set?

[Litjan]

Thanks for the report - we will look at it!

Jan

 

[dr_anthony]

Noticed also, in high ambient temp (Alice Springs YBAS +39 1800 ASL) full TOGA thrust actuated by AT not more than 84,8. Only recycle N1 limit on N1 page in CDU can fix that. 

[uppcan]

the same problem occured to me. No matter which derated TO thrust i select, the n1 gauge stucks at 84.7%

[Litjan]

We may revisit this at a later stage. The problem of A/T not setting correct thrust in some conditions is also on the review list.

Thanks, Jan

 

Edited March 3, 2017 by Litjan

[dr_anthony]

Would be correct in 1.3.1?

[Litjan]

Nope.