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FS2004 Flight Level question in AIFP

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unitedstates
Hi,

Been testing a flight plan for one aircraft traveling a few legs in a given day, just to see how it works. For the fun of it, on a (relatively) short flight from Northern to Southern California, I wanted to see what would happen if I set a large airliner (B737) to fly at FL 040. I'm almost certain there is no path from Nor to So-Cal that doesn't at have some mountains at least that high, so I wanted to test if an AI aircraft I had fly at that level would crash, and end its flight, or fly through the mtns and keep going.

Oddly enough, it ignored my command to fly at FL 040 and instead readjusted to a self-chosen FL 055. My question is, how did the plane know to do this all on its own? Did it analyze its own path and determine that based on all its waypoints, the lowest it could fly w/o hitting mountains was 5,500 feet? Or is it just a global correction that AIFP makes for all flight plans, and it won't let any plane fly a cruise alt below 5,500' no matter where I am? Or might it be a function of horizontal distance as well? Like if I was only flying 50 miles, it would accept 4,000'... but if I'm flying 200 miles, it finds 4,000' unacceptable... whether terrain is in the way or not... because it knows airliners aren't supposed to do that?

I haven't tried enough varied scenarios to see where the exceptions might lie. As I say, these were just experiments for the fun of it, to see what the plane would do. But if anyone has more insight as to how the simulator reacts to FL settings in AIFP, I'd be curious to know.

Oh BTW, I had this set as an IFR flight not a VFR, so maybe that made a diff? I already checked the manual for AIFP, and it really doesn't address the issue of setting cruise alt and how the planes behave-- other than to be sure to use the 3-dig hundreds format-- which doesn't really answer my question.

Thanks,

-- John

EDIT / FOLLOW UP:

Okay, well some correction to what I said. I've slowly been following the flight down south, and after leaving the hilly regions east of Monterey, it finally adjusted to a cruise altitude of 4,000' as I had programmed it down near Soledad/ San Luis Obisbo area headed toward Santa Maria. So apparently, it knew all along what alt I wanted it at. But it wasn't going to let the plane fly at it until it was certain the plane was past the higher hills that probably exceeded 4,000'-- or came pretty darn close. Just a guess, based on what I saw.
 
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gadgets

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First of all, it doesn't matter what altitude you set is you are not watching the AI aircraft and it is not in the originating or destination sector, because the Ai aircraft doesn't actually fly enroute unless you are watching it.

I don't know what would have changed your specified altitude but I can tell you it wasn't AIFP. When you program a leg, AIFP will "suggest" an altitude based on nominal aircraft cruise speed. For a 737, that "suggestion" would have been a lot higher than FL55 regardless of the distance involved. My guess would be that something in Flightsim triggered the change. Since it was a very short leg, the aircraft probably never entered the enroute phase. And, if you specified IFR, I suspect FlightSim will enforce the approach parameters, regardless of conflict with thre traffic file.

Perhaps someone elSe can add further detail.

Don
 
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167
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unitedstates
Actually, in this case I was following my AI by slewing my UA and "keeping with it". I wanted to test its behavior from orgin --> destin, hence the above question. I agree most people don't do this. They just let AI fly in and out of sector, and never follow just one... but I'm fascinated by their behavior so after making a flight plan of my own, I wanted to follow it. I'm learning by trial and error here. My approach to all this unorthodox at times, but sometimes I learn new and interesting stuff by discovering anomalies that I wasn't expecting, and then working backwards to try to determine why they happened in the first place.

I have since learned that as AI track from waypoint to waypoint, the new waypoint will determine new altitude assignments on the fly, as the AI plane continues forward. I have a copy of a flight map (an old FS9 module from 2005 I found somewhere), and it will indeed show the AI getting new alt assignments on their waypoints along the way. So I think I can conclude from that that the plane will get new assignments based upon how high the terrain is below. If I set it to FL 350, then there's no need to change it in cruise phase until TOD. But if I set it to an FL that was too low for upcoming terrain, it will have to adjust for my error (IF and only if... I manually inputted an ALT setting myself). Otherwise, I completely agree w/ you that AIFP sets a recommended FL automatically upon creation of each leg in the FP editor phase. Something I had forgotten took place, until I went back and did it over again. And if it's a big commercial jet-- like a SWA 737, it would indeed create an alt somewhere between say... FL270 and FL390. FL 040 would be unheard of.... unless I was making flight plans for an AI Cessna 200.

Thanks for your help... You'll probably see more posts of mine asking similar questions, as I continue to learn and explore this whole fascinating thing of making my own AI flight plans.

- John
 

gadgets

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ca-britishcolumbia
I have since learned that as AI track from waypoint to waypoint, the new waypoint will determine new altitude assignments on the fly
John, I think you'll find this happens only at the beginning of the approach and at the end of the departure. AI don't fly from waypoint to waypoint except on IFR approach/departure. And except when on approach or departure when the AI flies in accordance with its .air file, AI "fly" (see below) direct from airport to airport with their intermediate track and altitude predetermined by the traffic file . Neither AIFP nor any other flight planning program I'm aware of consider intervening ground elevation. specifying/confirming an appropriate FL is left up to the user.

As I think I may have mentioned in an earlier post, AI doesn't actually fly outside the originating/terminating sector unless being watched by the user aircraft. Otherwise, AI would place an impossible load on FlightSim. The traffic file specifies when and where the AI crosses sector boundaries - just in case you decide to monitor the AI in which case Flightsim must be able to determine where the AI should be. So, for the most part, intervening ground elevation is irrelevant.

Feel free to ask questions on new material. But, be aware that most questions you are likely to ask have already been asked and answered in these forums. So, you will find answers to most of your questions by scanning posts on the topic.

Don
 

tgibson

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Just to clarify, if the flight plan specifies an altitude too low for the terrain, FS will attempt to climb the aircraft over the terrain (usually about 1000 ft above it). But if the terrain rises too rapidly for the aircraft's climb rate, it will run into the mountain.
 
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unitedstates
Ok thank you for clarification there. That seemed to be what I noticed as well, or something very similar.
 
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