Uncommanded controlled AP descent

[Mudhendriver 3]

With the AP engaged ALT SEL set at cruise altitude (e.g. FL250) and alt knob set to 250, FMC set up for FL250, I got a controlled 1800 fpm descent to 11000...not sure why...even when I disconnected AP and leveled off...put the new altitude in the alt knob (aka VSI)...and reengaged AP, it wanted to continue the descent...question:  does the aircraft follow the default altitudes in the FSX GPS (flight planner) or the altitudes from an add-on flight planner like FSBuild?  Or, does that even matter?

 

As a swag that seems to work...I take off with @11,000lbs GW on a standard day from a 200 ft airport elevation and I use 112 V1, 118 VR, 125 V2 with 700 on the temps...

 

Rich Perry

[Jordan1995 6]

Are you using the FMC, or is it turned on? When I imported at plan, and If said plan had altitude restraints, the aircraft would follow those. Also if I had specified a cruise altitude in the flightplan of lets say, FL350 I would have to go to the FMC and change the altitude to climb higher. 

[Mudhendriver 3]

I did use the FMC and typed over the initial altitudes prior to taxi...which I believed contained altitude constraints...but once I thought you typed in new alts and hit enter you were GTG...I imported from FSBuild.

 

As an aside...takeoff distance with above data is 3400 feet with flaps at t/o....landing full flaps at @10000lbs GW sea level and standard day is an astonishingly short...like 2000-2500ft

[D-Micha 0]

I always use the FMC. As I noticed it controls only decents and only when I pushed the NAV-Button on the FMC. The Autopilot the decents to the altitude witch i have Input at the waypoint in the FMC.

 

Oh sorry, my english, I hope you understand me.

 

When i loaded a flightplan, or when i enter the waypoints by my self, the I DON'T push the NAV-button on the FMC.

The the autopilot climb and decents (when I push AltSel) always to the altitude what is selected with the Altitudeselector. No matte what altitudes are in the FMC.

 

So i think, the FMC only serves ist altitudes to the Autopilot when the NAV-button on the FMC is used.

[KenG 492]

As soon as you hit NAV on the FMS it hijacks the AP and will run its own internal routines for climb and descent to meet the altitudes you put into the box. (This is not how the NAV button works on any UNS1.) The other thing I found is the FMS does a poor job of maintain altitude once at altitude. (Have not rechecked since SP1.) The airplane will porpoise madly +- 1,000 feet.

 

If you are going to use the FMS use the FD, select GPS and allow it to provide LNAV only and manage your own VNAV profile.

 

This is the exact same UNS-1 that Carenado shipped with their B1900 and it has some of the same issues as it had in that aircraft.

 

FMS are hard things to program the real deals having millions of lines of code that large corporations have large staffs of software engineers working on and company pilots whose only job is to test and find errors. Even then errors do slip out into the wild. Carenado is no where near the size of Universal Avionics so I have to give them the "thanks for trying guys." Besides what is the alternative, six month wait as they try to replicate a UNS-1?