Auto Pilot Approach mod. problem

[BK 1]

It happend to me twice today with the 737NG 2d panel; Engaged the VOR/LOC mode aligned with the runway, and when the GS became alive armed the APP. mode. All this with Auto throttle in SPEED mode. At first all was nice and the plane followed the GS nicely. Suddenly Auto Throttle jumped to N1 mode and the plane lost the GS tracking, adding power and actually climbing up and APP mode jumped back to LOC mod only.This is quite strange as I already did autoland perfectly and I am puzzled at this.Anybody has an idea?ThanksBK

[afraj 0]

The Same thing happened to me several times before for some reason when i slow down to final approach speed before arming the app mode it works fine. and you can't slow down the aircraft to app mode while 15 miles out, usually not until you reach outer marker unless you are by yourself in the skies. so let's wait for an answer from the team to see if it is a bug.Best Regards Adib Afraj

[Guest ba747heavy]

Sounds like alpha-floor kicking in. What configuration were you in when the plane started climbing?

[Guest airtel]

Just a thought.... were you guys using FSNavigator at the time. The reason I ask is that I was using it with the follow flightplan option engaged and halfway down the approach it detuned both ils frequencies back to the last vor that i used. This naturally disconnected the autopilot couple approach. Just a thought.BTW I'm not critisising FSNavigator, but the idiot that was using it at the time....(ME) it was finger trouble. I now select the ils runway within it and hey presto, it tunes the nav receivers for me.

[crvm 0]

That's nice to know but what I think is going on is improper VREF causing the alpha protection to kick in. Please select APP REF and you MUST set the speed on the MCP with the A/T ON and SPD selected, if manual, then keep the speed VREF+5 or faster at all times on the APP...[h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-5/196432/winglets_lg.jpg

[afraj 0]

Randy thanks for your help i can now see it. but what's an alpha protection.Best Regards Adib Afraj

[Guest ba747heavy]

>Randy thanks for your help i can now see it. but what's an>alpha protection.>>Best Regards > Adib AfrajAlpha floor is the 737NG's way of protecting against stalls. Improper landing config is one way of making Alpha floor kick in.

[zubart 5]

What modes are engaged on the FMA (Flight Mode Annunciator) when this happens?Floyd

[BK 1]

I am not aware that the 737NG has an alfa floor feature. In any event it is unlikly as I was at full flaps extended, wheels down and autothrottle engaged watching speed for me.Thanks anywayBK

[BK 1]

The speed was set to the APP speed indicated in the approach page in the FMC but it was not VREF+5. It was just VREF. A/T was on and SPD selected.Question: What exactly do you refer to when saying "select APP REF"?Thanks RandyBK