bfisk
23rd Jul 2013, 11:17
Hello all.
I have a question regarding the 737-800 autothrottle thrust limit on takeoff, as computed by the FMC.
The other day, when entering takeoff performance data into the FMC, the AT thrust limit showed a split of about 0.8pp. N1. I can't recall the specific numbers, but something like a TO-2 and some assumed temp, gave us, say, a thrust limit of 90.0 and 90.8.
From the ensuing discussion, we observed from the QRH-PI that variations in bleeds, packs or anti-ice all could give differences in takeoff N1 of this magnitude.
However, for this time, all systems were "normal", ie bleeds on, packs auto and antiice off. This leads me to assume there might have been some kind of sensing fault somewhere, leading the FMC to "think" that one of the sides were configured differently from the other.
(Unfortunately I didn't write down the specific numbers, and I can't recall if the split was on the high or low side of the expected N1. It went into the log and I haven't been in this aircraft since so I don't know how maintenance solved it).
The question then becomes; what data and sensors are input to the FMC, to allow it to decide a taget takeoff N1?
Thanks a lot :)
I have a question regarding the 737-800 autothrottle thrust limit on takeoff, as computed by the FMC.
The other day, when entering takeoff performance data into the FMC, the AT thrust limit showed a split of about 0.8pp. N1. I can't recall the specific numbers, but something like a TO-2 and some assumed temp, gave us, say, a thrust limit of 90.0 and 90.8.
From the ensuing discussion, we observed from the QRH-PI that variations in bleeds, packs or anti-ice all could give differences in takeoff N1 of this magnitude.
However, for this time, all systems were "normal", ie bleeds on, packs auto and antiice off. This leads me to assume there might have been some kind of sensing fault somewhere, leading the FMC to "think" that one of the sides were configured differently from the other.
(Unfortunately I didn't write down the specific numbers, and I can't recall if the split was on the high or low side of the expected N1. It went into the log and I haven't been in this aircraft since so I don't know how maintenance solved it).
The question then becomes; what data and sensors are input to the FMC, to allow it to decide a taget takeoff N1?
Thanks a lot :)