here is a panel shot, it is supposed to be at 320 knots in a climb, instead it kept climbing while losing airspeed.

14.500 ft is hardly climbout.  Initial climb should be set to below transition height and then when cleared to climb by ATC you set your instructed altitude and push the knob in.  Then it's a managed ascent.

 

You may need to alter your VS to stop stall.

Have you tried try FL CH?

Is this a persistent problem, or a one time event? 

 

I'm noticing you are currently showing a tailwind.  Were you keeping an eye on what the winds were doing at this time?  Occasionally when wind directions between vertical levels are strongly different, the crap smoothing by FSX results in your airspeed dropping because you cannot accellerate sufficiently fast to keep it up as the wind swings around you.

 

Do you have any aftermarket weather engines running?

 

You certainly shouldn't have to use FLCH nor adjust your V/S manually during a properly configured VNAV climb, so I'd investigate other aspects first.

You could also have icing happening on your wing's leading edge, reducing loft.....and/or including engine intake.  This is easily overlooked,  I assume you have your Pitot heat on, right?

14.500 ft is hardly climbout.  Initial climb should be set to below transition height and then when cleared to climb by ATC you set your instructed altitude and push the knob in.  Then it's a managed ascent.

 

You may need to alter your VS to stop stall.

 

Sorry I meant it as accelerating past the 250 and 10000 restrictions.

 

Have you tried try FL CH?

 

VNAV climb shouldn't cause any problems

 

You could also have icing happening on your wing's leading edge, reducing loft.....and/or including engine intake.  This is easily overlooked,  I assume you have your Pitot heat on, right?

 

Anti ice was set to auto, everything else normal

Is this a persistent problem, or a one time event? 

 

I'm noticing you are currently showing a tailwind.  Were you keeping an eye on what the winds were doing at this time?  Occasionally when wind directions between vertical levels are strongly different, the crap smoothing by FSX results in your airspeed dropping because you cannot accellerate sufficiently fast to keep it up as the wind swings around you.

 

Do you have any aftermarket weather engines running?

 

You certainly shouldn't have to use FLCH nor adjust your V/S manually during a properly configured VNAV climb, so I'd investigate other aspects first.

 

I am using Active Sky 2012, and have seen the problem once or twice before.

I had this very same issue the other day, properly configured aircraft with correct trim settings, perfect roll out and climb, LNAV VNAV engaged, but at a certain point between FL290 and FL300 it went into overspeed and continued to climb past FL320 while increasing up pitch. However this only happened once out of some 10 flights and quite honestly never quite worked out what caused it. Disconnected AP, decreased trim, turned off VNAV, turned on FLCH and when reaching FL320 and speed returned to what it should have been turned on VNAV again and had no further issues. Aircraft was fully loaded with cargo but not with fuel since it wasn't a long haul flight. Not too concerned about it.

 

Regards

I had this very same issue the other day, properly configured aircraft with correct trim settings, perfect roll out and climb, LNAV VNAV engaged, but at a certain point between FL290 and FL300 it went into overspeed and continued to climb past FL320 while increasing up pitch. However this only happened once out of some 10 flights and quite honestly never quite worked out what caused it. Disconnected AP, decreased trim, turned off VNAV, turned on FLCH and when reaching FL320 and speed returned to what it should have been turned on VNAV again and had no further issues. Aircraft was fully loaded with cargo but not with fuel since it wasn't a long haul flight. Not too concerned about it.

 

Regards

 

Same situation here, almost fully loaded with cargo, I believe I set it to around 80%, but light fuel.

The speed decreasing in VNAV mode while climbing is a known problem, see the issue tracking thread. It's also been mentioned in these forums. For some reason the speed seems to reduce to minimum whilst flying certain SID's. I've found that it's from routes that are saved then entered in to the FMC via Route Request. Loading the route manually seems to avoid this.

+1 i have this issue also with speed reducing down to stall speed in vnav

 

Michael Moe