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Pin Head
8th Dec 2018, 14:29
Hi

had an arrival RtA for the FAF the other night. Selected and behaved for the most. Then once in the TMA it gave differing command speeds on each PFD and vastly different VNAV altitude deviation scale information.

thoughts?

ManaAdaSystem
9th Dec 2018, 19:14
Hi

had an arrival RtA for the FAF the other night. Selected and behaved for the most. Then once in the TMA it gave differing command speeds on each PFD and vastly different VNAV altitude deviation scale information.

thoughts?

ęNormalĽ for the NG. I donít know why. Itís worst when you get a low speed RTA. The way to avoid it is to use the computed speed and MCP SPD.

Skyjob
10th Dec 2018, 19:14
Not just when using RTA...
Some versions of FMS software load sometimes remain in level flight and therefore reduce speed after TOD while profile already descends, then command a pitch down to accelerate and intercept from above and settle back onto path and target descent speed.
Odd behaviour, never fully worked out what problem was, nor able to document it in video so to ask Boeing as it is so random when it happens.