Hello Everyone,I have been flying with the PMDG 744 pax version on VATSIM for the past few months now and have found that the climb performance is fine up to about FL240 or so and then deterioriates sharply to the point that the plane can barely climb at 100-200 fpm, especially when above FL250. Yesterday and today, I did two tests: Both were using the exact same saved flight plan (created with FSBUILD) from KATL to EDDM, a flight I recently completed on VATSIM and on which I had real issues with reaching even FL310. The first test was with ASV6 on the second was with it disabled and using clear weather, setting CLEAR WEATHER option in FSUIPC (version 3.60). The amount of fuel and ZFW in each case was identical. FYI, here are my parameters for weights:PAYLOAD = 139,680 lbs. (full pax, partial cargo/baggage)ZFW = 533,768Planned GTOW = 850,230 lbs.TOTAL FUEL = 318,400 lbs.Initial cruise altitude - FL330.The FMC indicated Optimizer cruise at FL300 and max. at FL343.With ASV6 enabled, my climb rate was reduced to a crawl after FL250. I noticed that the plane had to basically stop climbin altogether to maintain the FMC-recommended climb speed for maximum angle (which was around 288 KIAS at this FL). With ASV6 and all weather cleared, the climb rate was around 600 fpm and I reached FL310 comfortably, leveled off for maybe 50 NM and then climbed further to FL330. In both tests, I used THRUST LIMIT setting in FMC of either GA or CON to increase climb rate.I noticed with ASV6 enabled that the airspeed fluctuates up and down and causes the plane to reduce its climb rate as it tends to lose air speed and it takes a good HOUR to climb to FL330!Here is my options screen for ASV6. Could any of these have an effect on the climb rate?As far as I can tell, I have filled in all FMC options properly so it is ASV which is causing an adverse effect.Any help would be appreciated.Johnhttp://forums.avsim.net/user_files/151807.jpg

Actually, I think I know why my climb performance is low. It's simple really: because I am too heavy. After carefully studying page 2-9 of the PMDG manual under step climb section, I realized that my GTOW of 850,000 lbs means that I can only hope to reach FL310 but that to go any higher to FL330 means I have to burn off over 1 hour of fuel!Sorry for the trouble. I thought I had studied these charts from PMDG but I must have forgotten that my weight was more than the maximum indicated in the charts to reach for first FL (of 300).But, it does remain that the speed DOES fluctuate WITH ASV6 but is steady without any weather, probably due to winds aloft.John

Hi John,Use Update Suppression should be On and then increase your suppression range to 250.Hope this helps,Jimhttp://www.hifisim.com/Active Sky V6 Development Team Active Sky V6 Proud SupporterHiFi Beta TeamRadar Contact Supporter: http://www.jdtllc.com/AirSource Member: http://www.air-source.us/FSEconomy Member:http://dot.kelder.net:8080/fseconomy/

Byrna:But, it does remain that the speed DOES fluctuate WITH ASV6 but is steady without any weather, probably due to winds aloft.This is a known problem with FS. It's changing the airspeed relative to the aircraft, instead of aircraft speed relative to ground when wind change.

I'm not so sure that's really a problem. I fly a Cessna 172SP in real life, and on long x-country flights, the IAS will definitely oscillate from time to time. And in gusty conditions, IAS can change drastically, +/- 10 kts or even more at a time.

Thanks for the setup info Jim.I'll try changing the settings next week before I fly again.John

Autopilots use IAS, not ground speed, as a speed reference. That is one reason why IAS is changed to Mach measurements at higher altitudes and airspeeds. If autopilots used ground speed there might be cases where the aircraft flight envelope could easily be exceeded in encountering the effects of headwinds, etc., nor take advantage of shortening flight time due to tail winds. That's why winds aloft is taken into consideration for choosing an appropriate cruise level. As you cross various flow patterns (such as jet stream currents) IAS will change until thrust adjustments can compensate. When you use AS6 winds aloft is generated and also thermal and other vertical currents. Both thrust and pitch are used to maintain both altitude and airspeed. With FS in the Clear Weather Theme it is basicly fantasy land so all appears steady and only trim would need occasional manual adjustments without any AP engaged. It is thermals, winds aloft, surface countour effects on vertical drafts (such as mountain winds and wind wash over mountainous or rolling terrain, and even temperatures aloft that command the attention of an autopilot so the pilot can attend to other duties.

Hi:I too have very poor climb performance throughout the entire flight. I'm using the pic 737, it usually climbs quite well at 118,000lbs. I have not tried the 747 yet. Very interesting though. I'm not sure what the problem is.Todd

Hi,Perhaps you are experiencing warmer upper-air conditions as is common this time of year?Remember that performance is decreased with increased temperature. This may or may not explain things but it's certainly likely.Best,-Damian

That's interesting Damian. I did notice that my climb performance was better during the Winter-Spring months I have to admit. Also, this supports my test using CLEAR weather theme with no ASV because climb performance was around 800fpm when quite heavy (GTOW of 850,000 lbs) with the 744 whereas it was barely climbing with ASV6 enabled (e.g. around 100-200 fpm).However, in order to test this I'll have to try cold temperature winter theme with ASV6 offline using weather themes and ASG.John