Constantly rising/dropping airspeed in CRZ with Vista/FSX

[Richard McDonald Woods 168]

Today, without restarting a flight (i.e. starting a new flight from the ground) I had uncontrollable sudden increasing/decreasing speeds whilst in cruise. Occasionally the aircraft will increase both speed and FL without provocation. At other times the speed just increases/decreases on its own until stick shake. On the current flight, A/P is commanding M.838 at FL310, but the speed sometimes gradually/suddenly increases to over M.90 and decreases to M.708 without interference.Cheers, R

[downscc 1,327]

Yup, common problem in FSX. Seems to be worse than similar problem in FS9. Been several recent threads on wind and pressure shifts.Did you notice that the wind vector was changing direction/velocity?ActiveSkyX just released SP2 that seems to be real close to fixing the problem.

[Richard McDonald Woods 168]

Hi Dan!No, my problem was after installing ASX SP2. I noticed nothing different with it.Cheers, Richard

[downscc 1,327]

I recommend you join the multiple threads running on this topic next door in the HiFi forum. The ASX SP2 seems to work for most, but there are still problem reports, and the guys at HiFi are asking for feedback to continue the improvement of their product.Not much PMDG can do about the weather. Seems that the worst that happens is minor changes in IAS/ALT that cause small power changes seem amplifed by the engine sounds. There might be something there for PMDG to consider.

[Richard McDonald Woods 168]

Flying today with Win/XP 400X, I again had the sudden increases and decreases in IAS. Eventually the A/P seemed to give up and let the airspeed gradually bleed away until stick shake. Afterwards, I was taking another look at the Advanced Operations Tutorial by Holger Seilz. He talks about setting the cruise speed (e.g. to .84) on the SEL SPD prompt on the CRZ page. As I haven't been doing this to date, I just wondered whether there is a bug in the cruise logic where not explicitly setting a value caused the erratic operation of IAS in cruise.Just a thought that might help the investigation.Cheers, Richard

[Guest fyrestrtr]

Hey Richard: IME (In My Experience) it is not an issue with the cruise logic, as I have not experienced this in the many hours I have enjoyed PMDG products (including the 747). It seems to stem from the ever popular weather system. I have experienced this when there is a lag in updates of the weather; or when you disable real time weather midflight. I was doing circuits and during cruise -- I just disabled the weather since it was not downloading properly. All of a sudden; the aircraft starting this nice bobbing action, where the speed would jump, then settle (MCP was on VNAV/LNAV). I eventually sorted it by clicking on the SPD mode button on the MCP. Gotta love weather :)HTH

[Gary A 8]

Just to add my support I have the same issue. To add even on the ground sometimes the plane is rocking back and forth like I am in heavy turbulance. problem is there more often than not but not always.Vista, GoFlight throttles and other, CH yolk and pedels, ASX and ASX Graphics with SP2, registered FSUIPC, online using FSINN 1.3 and yes FSINN weather is off.>Today, without restarting a flight (i.e. starting a new>flight from the ground) I had uncontrollable sudden>increasing/decreasing speeds whilst in cruise. Occasionally>the aircraft will increase both speed and FL without>provocation. At other times the speed just increases/decreases>on its own until stick shake. On the current flight, A/P is>commanding M.838 at FL310, but the speed sometimes>gradually/suddenly increases to over M.90 and decreases to>M.708 without interference.>Cheers, R

[Richard McDonald Woods 168]

Guys!At last (perhaps my 10th attempt) I have managed to fly EDDK-KSFO!With FSX SP2 and ASX SP2 installed without additional stations, the flight was successful, including saving my flight over northern USA and restarting the next day (although the aircraft was initially very lazy). Over the N Atlantic I had around 5 occasions when the aircraft suddenly gained/lost air speed to stick-shake, and I had a couple of overspeeds. Then things became quieter over Canada. So I started thinking that the problems were oceanic in nature. But eventually, over the USA, I started getting the same old surge problems, both before and after the restart. On all these surge occasions, the wind direction was switching about quite violently, and quite contrary to the on-line FL300 weather map.Once I started the descent into KSFO things quietened down and I had a very pleasant approach into RWY 28L. I really feel a deep sense of achievement after 12:45hrs!So now I shall start the long haul back to EDDK.Cheers, Richard