FMC N1 and topcat N1 % difference

[CaptKornDog 282]

I'm just happy when the power levers line up together.

Not a fan of the 1" lever split takeoff?

 

(Nor am I)

[JoeDiamond 67]

A couple of tenths difference is not a big deal.  As part of our load closeout process we compare the FMC calculated N1 with the one given in the takeoff performance.  As long as the actual N1 is in the ballpark it's all good.

 

If it's off by a substantial amount then something isn't right and you should figure out the cause.  There is a known anomaly in the real plane that can cause the wrong temperature to be uplinked into the FMC.  In one case the actual temperature was 18C and the uplinked temp was -18C.  The crew didn't catch it and they took off with substantially less power than planned.

 

Another thing I look for when checking the values is that the FMC calculated N1 is the same for both engines.  If they are different then you probably have either a pack or an engine bleed switch off.  There are times where a split is normal, if you had a pack MEL for example.

[Driver170 42]

A couple of tenths difference is not a big deal.  As part of our load closeout process we compare the FMC calculated N1 with the one given in the takeoff performance.  As long as the actual N1 is in the ballpark it's all good.

 

If it's off by a substantial amount then something isn't right and you should figure out the cause.  There is a known anomaly in the real plane that can cause the wrong temperature to be uplinked into the FMC.  In one case the actual temperature was 18C and the uplinked temp was -18C.  The crew didn't catch it and they took off with substantially less power than planned.

 

Another thing I look for when checking the values is that the FMC calculated N1 is the same for both engines.  If they are different then you probably have either a pack or an engine bleed switch off.  There are times where a split is normal, if you had a pack MEL for example.

 

Brilliant

[Copper. 78]

A couple of tenths difference is not a big deal. As part of our load closeout process we compare the FMC calculated N1 with the one given in the takeoff performance. As long as the actual N1 is in the ballpark it's all good.

 

If it's off by a substantial amount then something isn't right and you should figure out the cause. There is a known anomaly in the real plane that can cause the wrong temperature to be uplinked into the FMC. In one case the actual temperature was 18C and the uplinked temp was -18C. The crew didn't catch it and they took off with substantially less power than planned.

 

Another thing I look for when checking the values is that the FMC calculated N1 is the same for both engines. If they are different then you probably have either a pack or an engine bleed switch off. There are times where a split is normal, if you had a pack MEL for example.

Thanks Joe!

 

Brian Nellis