I wonder if any of the 737NGX wizards have an answer to this. Woukd be appreciated.Done many, many flights with the 737NGX from the-600 to the -900.Just took off from CYVR, aircraft prepared, trimmed, etc using TOPCAT. VNAV, LNAV, N1 take-off. Clean take-off at V2. At 1500 feet, went as usual to select AP, and it would not engage at all, and FMC flashing 'Buffet Alert'(using Jeppessen downloaded weather). No matter what I tried, could just not get AP to engage. Same aircraft, Air Canada 737-800Wl flown without a hitch from KHOU-CYVR.Returning to CYYZ.Additionally, after downloading and installing Jonathan Gabbert's freeware CYVR, am getting weird patches as if I'm taxi-ing on water(see pic). Any ideas. Thanks

Aircraft out of trim?

Aircraft out of trim?

Cannot be as I have already set the trim as indicated by both the FMC and confirmed by TOPCAT while still at the gate, which for a fully fuelled aircraft going from CYVR-CYYZ was 6.65 units.

Cannot be as I have already set the trim as indicated by both the FMC and confirmed by TOPCAT while still at the gate, which for a fully fuelled aircraft going from CYVR-CYYZ was 6.65 units.

Yeah, but then you start to accelrate past VR witch your trimmed for then you need to trim down as you speed up, or you can just turn realistic AP engament off.

Edited February 1, 201214 yr by VLJ510

Yeah, but then you start to accelrate past VR witch your trimmed for then you need to trim down as you speed up, or you can just turn realistic AP engament off.

Ah, well, now, you may be on the right track there. Because the previous KHOU-CYVR leg was a lighter fuel load, hence no probs. This tip is definitely worth looking into as I was under the impression that the trim remained the same upto Vr and climbout acceleration. Thanks.