Strange In-Flight Occurrence

[Guest ttownsend]

Hello Captains!I'm sure this has more to do with FS9 than it does with the PMDG 737, but since I happened to be flying that aircraft at the time, I figured I ask here in this forum first. I had a very strange occurrence which I'm hoping someone might have an explanation for. Early this evening, I was flying between Denver (KDEN) and Boise (KBOI). My flight plan had me on J154 to J20 to J54 at FL350. At some point, I flew over OCS and turned onto J20 toward PIH. I was at cruising altitude, Mach .810, weather was clear and the FMC was in control. No problems whatsoever. However, about half-way between OCS and PIH, I suddenly noticed that the aircraft was climbing rapidly. The altimeter on the EFIS indicated I was now at 36200 and climbing. At that same time, ATC came on and told me that I was 500 feet BELOW my assigned altitude and to climb to FL350. I then pressed SHIFT-Z to see what FS9 would indicate for altitude, and it said I was now at 60000+ feet MSL and climbing. So, I disengaged the Autopilot and took manual control of the aircraft. I tried to force the nose down a bit to lose some of the altitude, but even though the FS9 display indicated that I was in fact decending slowly, the altimeter on the EFIS was still indicating an increase in altitute, and ATC was still yelling at me to expedite my climb to 350. Meanwhile, my airspeed indicators were all over the place, going from IAS 650 to IAS 29 and back again in a matter of seconds.No matter how many times I tried to reset the systems, every time I re-engaged the A/P, the aircraft would nose-up almost vertically and, at one point, FS claimed I was over 100,000' MSL.Finally, I went into slew mode, set the aircraft to level, and then slewed the rest of J20 and half of J54. By now, I was only about 120nm away from Boise, and when I went back into normal mode, I was able to re-engage the VNav and LNav and the remainder of the flight was perfect ... (one of my better landings, I might add! :} )So now, Captains, does anyone have a clue what went wrong, or perhaps what I did wrong?Thanks in advance for your comments.- Tom Townsend

[crvm 0]

Were you using add-on weather?[h4]Best Wishes,Randy J. Smithhttp://www.precisionmanuals.com/images/betaimg.jpg

[Guest Brian W]

Tom,I had the same thing happen to me today as well. I was enroute from KSLC to KBIL. I was just reaching my T/C (over KLGU), when all of the sudden my airpeed went to about 430 KIAS. Although the indicated winds aloft was still around 305 at 98kts. I quickly disconnected the AT and reduced power to idle. At this time I also had a loss of indicated altitude. The altimeter was quickly decsending to sea level although Shift-Z was showing a true altitude of FL300. I decided to reset the flight and start from KLGU. With the aircraft on the ground I hit "B" and was suprised to see the altimeter at 40.11!! Setting the altimeter to 29.92 gave me an altitude far below sea level even though the field elevation is 4454'. I suspect you were using real weather as I was, and fell victim to an incorrect altimeter setting from that area. I ended up turning off real weather until I started my desent into Billings and had no problems after I did that.Brian WKRNT

[Guest ttownsend]

>> Were you using add-on weather?>>>[h4]Best Wishes,>Randy J. Smith>http://www.precisionmanuals.com/images/betaimg.jpgYes, I had real weather turned on with periodic updates. - Tom

[Guest ttownsend]

>I had the same thing happen to me today as well. I was enroute>from KSLC to KBIL. ...> ... I ended up>turning off real weather until I started my desent into>Billings and had no problems after I did that.>>Brian W>KRNT Hmmmmm...of everything I tried to correct the problem, the one thing I *didn't* try was turning off the real weather. Didn't even think of it. However, that would explain why things suddenly got better once I "slewed" out of the area. Thanks for the response. If it happens again, I'll know what to try first.- Tom

[Guest Bob Kellett]

The same thing happens repeatedly on a KSEA to KDEN flight, always just after crossing PIH. The airspeed starts climbing to over 700! The altitude on the PFD says I am descending quickly but I am actually climbing at over 6000 fpm, until the aircraft overstresses! This is with real weather with periodic updates turned on. It hasn't happened on any other flight yet, just when crossing PIH.Bob Kelletthttp://www.opticsmall.com/VirtualAlaska/737700-.jpg

[Vulcan 14]

If you were using an add-on weather generator I suggest you advise the authors, especially if you can pin-point the weather station(s) or area.If you using FS weather then I guess no amount of writing to MS will effect a fix, until FS10 (perhaps)!