Originally Posted by
Check Essential
Ok, I gotta agree with that one.
Delta guys should not be bragging about the VNAV on our 737s.
When it comes to VNAV descents, the Smiths FMS on Delta 737NGs is a piece of junk.
It does OK in climbs or down low at low speeds (ie -- approaches). But in a descent from cruise it never seems to get it right. It is highly likely to overspeed the airplane, overshoot the crossing restriction or get 20 knots slow. (or all three)
The Honeywell VNAV on our 757s and 767s is far superior.
I agree with you on the Smiths/Honeywell comparison. HW uses an algorithm to predict winds, Smiths uses last input. One thing that helps is descending a little early, say 10 NM.
What do you put in for "Forecast Winds" on the decent page? Anything reasonably close will forestall a VNAV Disconnect. I jumpsat on CAL NG years ago, and they were sent via ACARS pretty accurate Forecast Winds before descent, and it was pretty damn precise. I've put relatively old and inaccurate winds in and it's better than nothing.