777 autopilot/control problem

[kevinh 409]

ISA+10 at FL 370 would mean OAT of -48°C (ISA OAT @ FL370=-58°C).

Indeed, but OAT is not TAT.

My rule of thumb was that with climbing through FL280 an OAT of -40°C (=-40°F!) would be equal to standard and the higher you get the smaller should be the difference to ISA temps. 10°C of difference at FL370 is IMO an indicator for high altitude hot air updraft (moisture), which is "normally" followed by an intermediate (but probably severe) downdraft (cooler air) when "on top" of the cell (air mass effect).

 

Maybe there are some severe updrafts/downdrafts below the OP's routes going on which cause the A/P to react strange and gets the A/C out of control when trying to fly it manually?

Probably turning on FSX's thermal visualization could show the updraft and prove that problems start when entering that zone.

 

BTW: on the OP's screenshots in post #6 there are quite some CUs/CBs during climb on his route and below him. In the end on the last two screenshots the sky is perfectly blue. Maybe just a WX simualtion flaw with an abrupt change of values?

 

Happy new year,

Claus B)

FL280 would an OAT of approximately -40 deg C (-40.44 in fact) but your rule of thumb makes no sense. For an ISA+10 day, OAT will be 10 deg C above standard day for all altitudes a 777 can operate at. Your first sentence contradicts your rule of thumb too.

 

I've no idea whether thermal effects are simulated in FSX at that altitude, but PMDG recommend switching them off anyway.

 

Anyway according to the OP's post (above yours) his problem is related to having the TERR display active on both sides, so not weather related. In my experience the TERR display seems to increase VAS usage so having it active on both sides could be a big hit and might cause problems with the sim. Not sure why you would have it switched on at that altitude though.