South Pacific Anomaly

[PropStrike]

I'm flying over the South Pacific and am running into some problems with FS2002. I'm wondering if anyone else has encountered the following and if they know of any fixes:

Background:
I'm flying from Auckland, NZ (NZAA) to Buenos Aires, Argentina (SAEZ) in a B747 (standard FS2002 Global Freightways model). I have used the Flight Planner to create a route close to a great-circle route, with most of the flight taking place over the South Pacific Ocean (> 50 deg South latitude). I have loaded real-world weather, and have a tailwind of almost 65kts at an altitude of 37,000'. The flight is under air-traffic control. I have been able to take off, ascend, and attain cruising altitude under nominal conditions. I then go to autopilot and auto-throttle and am on autopilot for several hours.

Problems:
1. About 3-4 hours into the flight, I am cruising at 37,000' at Mach 0.85, with a ground-speed of about 550kts (strong tailwind). All of a sudden, my IAS (Indicated Airspeed) shoots up to about 400KTS, and the "Overspeed" indicator flashes. My speed shows at about Mach 1.l5 and the auto-throttle scales back the throttle to almost idle, until my speed is reduced to Mach 0.85 again. Now, because I've "slowed down" considerably, my groundspeed (shown in the GPS window) indicated 250KTS. I've checked the tailwind, and it's still a 65KT tailwind.

2. Another 1-2 hours later, (cruising at 37,000', Mach 0.85, 250KT groundspeed), my IAS goes down to 120KTS, and my altitude drops to 25,000' almost immediately. The auto-throttle tries to compensate by giving full power, but because autopilot is set to Mach 0.85, I quickly get into an unstable condition where I stall. I am able to manually bring the aircraft back to Mach 0.85 and 37,000'. At this point, GPS shows a groundspeed of 491KTS.

3. Another 1-2 hours into the flight, the problem I encountered in #1 shows up again, except this time, instead of only going to 400KTS indicated, I shoot up to 50,000' almost immediately. I then have to take the aircraft off autopilot and manually maneuver it back to nominal flight conditions. The groundspeed shows about 250KTS again.

I haven't gotten further than this in the flight, but I'm sure step #2 will show itself again while the aircraft tries to get back to a more "Normal" groundspeed of about 500KTS.

Sorry for the amount of detail, but does anyone have a clue as to what's going on here? I've taken many flights over other parts of the world, but this is the only time I've seen this behavior. I've never flown over the South Pacific before, so I thought that might be part of the problem. Any help is appreciated.

Thanks,

PropStrike

[BFMF]

That's wierd, never had that happen. Of course, it's been months since I even flown anything heavier then a biz jet

[Paz]

 I wonder if as you burn fuel, and the aircraft becomes lighter, maybe it's freaking out the program?
Just a thought.

[BFMF]

[quote]

[PropStrike]

I flown long routes using the same aircraft in other parts of the world and haven't had the same problem, so I don't think lighter fuel load is the issue. The only thing I can think of is that weather is either undefined or (somehow) poorly defined in the South Pacific. During one of these times when the a/c goes haywire, I've noticed that when I reset the altimeter (pressing "B") the altimeter is reset to 18.80", which is obviously very wrong. I think this probably has something to do with the problem.

[BFMF]

Does this phenomena occur with the weather cleared?

[Bazza]

Interesting stuff........

I've physically flown from Auckland to both Australia and Singapore a number of times and have been amazed at the jet-stream tailwinds experienced.    I've sat in the cheap seats and watched the airspeed indicator on the movie screen creep up to close to the speed of sound levels.    This is a known phenomenon and no doubt taken into account by the air-lines flying the area.

Having said that, I doubt very much that Bill Gate's buddies have written it into the program

[Ivan]

I'm flying over the South Pacific and am running into some problems with FS2002. I'm wondering if anyone else has encountered the following and if they know of any fixes:

Background:
I'm flying from Auckland, NZ (NZAA) to Buenos Aires, Argentina (SAEZ) in a B747 (standard FS2002 Global Freightways model). I have used the Flight Planner to create a route close to a great-circle route, with most of the flight taking place over the South Pacific Ocean (> 50 deg South latitude). I have loaded real-world weather, and have a tailwind of almost 65kts at an altitude of 37,000'. The flight is under air-traffic control. I have been able to take off, ascend, and attain cruising altitude under nominal conditions. I then go to autopilot and auto-throttle and am on autopilot for several hours.

Problems:
1. About 3-4 hours into the flight, I am cruising at 37,000' at Mach 0.85, with a ground-speed of about 550kts (strong tailwind). All of a sudden, my IAS (Indicated Airspeed) shoots up to about 400KTS, and the "Overspeed" indicator flashes. My speed shows at about Mach 1.l5 and the auto-throttle scales back the throttle to almost idle, until my speed is reduced to Mach 0.85 again. Now, because I've "slowed down" considerably, my groundspeed (shown in the GPS window) indicated 250KTS. I've checked the tailwind, and it's still a 65KT tailwind.

2. Another 1-2 hours later, (cruising at 37,000', Mach 0.85, 250KT groundspeed), my IAS goes down to 120KTS, and my altitude drops to 25,000' almost immediately. The auto-throttle tries to compensate by giving full power, but because autopilot is set to Mach 0.85, I quickly get into an unstable condition where I stall. I am able to manually bring the aircraft back to Mach 0.85 and 37,000'. At this point, GPS shows a groundspeed of 491KTS.

3. Another 1-2 hours into the flight, the problem I encountered in #1 shows up again, except this time, instead of only going to 400KTS indicated, I shoot up to 50,000' almost immediately. I then have to take the aircraft off autopilot and manually maneuver it back to nominal flight conditions. The groundspeed shows about 250KTS again.

I haven't gotten further than this in the flight, but I'm sure step #2 will show itself again while the aircraft tries to get back to a more "Normal" groundspeed of about 500KTS.

Sorry for the amount of detail, but does anyone have a clue as to what's going on here? I've taken many flights over other parts of the world, but this is the only time I've seen this behavior. I've never flown over the South Pacific before, so I thought that might be part of the problem. Any help is appreciated.

Thanks,

PropStrike

Were you passing the international dateline?
Did your flight path take you over 80 degrees south?

[PropStrike]

Yes, I did pass the Int'l date line (east of New Zealand). This was not the location of the discontinuity, however.

No, I did not go as far as 80deg South.

[packercolinl]

I've had a similar problem with the default 747 in the South. After numerous attempts I've given it away as a M$ glitch.

[fisharno]

I don't think the weather could be depicted that accurately to be able to give you high jetstream speeds, with huge up and down drafts.

Could it?  

[BFMF]

I've downloaded real weather with winds aloft and up high it's not uncommon to have winds at 100knts

[PropStrike]

Hello Folks,

Thanks for all of your comments. I've done a little more digging and I've found the following:

-When I fly with no weather "Clear all weather" option, this problem does not occur, so somehow the problem seems related to the weather download.
-One clue to the problem is that when I reset the altimeter in one of the problem areas, it gets reset to about 18" rather than the normal 29.92".
-I looked into this further and found that there is a problem in the "Temp/Pressure" tab of the "Advanced Weather..." feature in the weather page. On that tab, when I am in one of the affected areas and I click on the 34,000' Temp/Pressure bar (the one that controls the Temp/Pressure between 34000' and 39000'), the text box for Altitude shows 121' instead of 34,000'. So, somehow, the pressure at 34,000' is not being set properly because of this. Even when I try to manually set the reading to 34,000' it gets reset to 121'.

I'm still not sure what's causing the barometer reading to be off, but there is definitely a problem in this section of the weather setting. If anyone can suggest a workaround to this, it would be appreciated. If not, I'll simply have to fly without downloading weather when I do South Pac flights.

PropStrike

[packercolinl]

I rarely fly that high but I believe that once you go over a certain height you revert to a standard pressure setting regardless of the existing pressure. This provides a level playing field so to speak for all aircraft operating at those levels. I may be confusing things here!
The other thing is that I have used smaller jets on occasion both ways across the South Pacific and had some huge rides(tailwinds) and also had to hunt up and down for favourable winds. The only time I've had problems as I said before was with the FS747.

Best of luck,Cheers

[PropStrike]

Regarding the comment by packercolinl, "I believe that once you go over a certain height you revert to a standard pressure setting regardless of the existing pressure." you may be right if the flight is above 39.000', because there is no wind-aloft definied above 39.000' in the weather download. In my case, however, I am flying at 37,000', and the wind aloft is definied for both 34,000' and 39,000', so the downloaded weather applies. Somehow, the downloaded weather is corrupting the weather information for this part of the world. Clearing the weather completely solves the problem (but is obviously not the best solution).