tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80 Reply 2, posted (3 months 3 weeks 6 days 19 hours ago) and read 878 times:
Quoting smartt1982 (Thread starter): On the inflight landing calculations for the 737-800 for a Dry runway with Auto brake 3, there is no corrections to apply for the slope of the runway
Strictly speaking, there is a correction, it just happens to be zero for that particular combination. For the same slope on other runway surface conditions, it's non-zero.
Quoting Max Q (Reply 1): Why would you need a slope correction for an autobrake setting ?
I was wondering that too, but I think it falls out of the way landing distances are calculated...they come off actual data and, with slope, if you cross the threshold at the correct height your touchdown point is going to move a little bit. The roll distance from the time the brakes come on shouldn't change with slope for autobrakes, but the distance from the threshold to the start of braking will change.
If you look at some of the data, there are obvious trend reversals, which wouldn't happen if you were doing analytic solutions but can happen if you're generating the data with actual performance landing data.
vikkyvik From United States of America, joined Jul 2003, 8228 posts, RR: 28 Reply 3, posted (3 months 3 weeks 6 days ago) and read 757 times:
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Quoting tdscanuck (Reply 2): I was wondering that too, but I think it falls out of the way landing distances are calculated...they come off actual data and, with slope, if you cross the threshold at the correct height your touchdown point is going to move a little bit. The roll distance from the time the brakes come on shouldn't change with slope for autobrakes, but the distance from the threshold to the start of braking will change.
That's certainly true. For a standard 3 degree glide path, 50 foot TCH, and discounting flare, your touchdown point will move like so:
(that's of course assuming the main gear is at 50 feet when crossing the threshold)
As far as autobrakes go, with a constant deceleration rate, the brakes simply won't have to work as hard if you're landing on an upslope. They'll have to work harder if you're landing on a downslope.
Is that the basic gist of it?
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