can someone explain to me why AP keeps stalling my aircraft? i have fspassengers and have got through all classes of props and am now onto jets - i therefore am choosing to fly longer distances. I took off last night from Heathrow for an early morning flight to Tenerife and after 10 minutes got to my assigned altitude set the throttle back slightly and set to no flaps. I spent 5 minutes just sat there to ensure speed didnt drop too slow... gave my passengers a movie to watch and a meal and then set autopilot to keep me at FL310 and set speed to 16x. I went downstairs for 5-10 minutes and came up to check in with ATC (hate having to do this!). Upon my return i was shocked to see that my passengers were in uproar that i had "nosedived" down to FL150 - i set the sim speed to normal and the bloody ap tried to climb to FL310 and stalled. Passengers started to bang on my cockpit door and all of a sudden i found that i had wasted 2 hours of my evening. The autopilot does seem to keep stalling the aircraft and this is becoming quite annoying now, does anybody know why the autopilot allows this to happen? or do you have any advise on the correct use of the autopilot?regards

It would be very helpful if you would tell us what airplane you were flying. Thanks.Bob..

Have you checked your aircraft config? It should look basically like this:[autopilot]autopilot_available= 1flight_director_available= 1default_vertical_speed= 1800autothrottle_available= 1autothrottle_arming_required= 1autothrottle_max_rpm= 98autothrottle_takeoff_ga= 1pitch_takeoff_ga= 8use_no_default_pitch= 1I've never experienced your problem and all of my heavy iron is set up this way.Sorry, no other ideas.Bob

last night i was flying a 737 when i experienced the problem reported. I will check the aircraft.cfg as suggested. Thanks as always.

Couple of questions that your answers to would be helpful in solving this problem.- What type aircraft are you flying? ok I see 737 - What is your gross weight at cruse Flight level?- What is your target cruse speed?- Is speed hold engaged at altitude to maintain target Mach while you are away from computer(A lot can happen very quickly at 16 times)- At what point in your flight do you retract the flaps?The autopilot, with altitude hold engaged, will chase the altitude in a stall situation. A little deviation from altitude is ok for it to handle but a complete stall is another thing. To confirm this for yourself you can climb the aircraft to altitude and set altitude hold establish cruse speed, then when all is stable cut power to idle thrust and watch as the aircraft maintains altitude while applying nose up trim, As the speed decays further the nose up trim will continue to increase, the aircraft stalls and then the autopilot will increase the trim to the stops but will not attempt to recover from the stalled and out of trim condition and the A/C will mush all the way down to terra firma. Instrument indications are: High sink rate and altitude loss, Very high nose up attitude, low airspeed ears popping, pax screaming, attendants calling etc etc co-pilot praying.Douglas:-bigangel

Is your pitot heat on?

Number one: Gross weight?Speed setting?Rate of climb (also competing as number one)?Gear and flaps retracted?Fuel/load distribution?With many aircraft, particularly heavies you may have to either step climb, or periodically reduce your rate of climb in order to maintain acceptable true air speed as you reach higher altitudes. Obviously you cannot leave the cockpit during those times. (Real world included)Also with some flightsim aircraft, you will find that the dynamics are such that you will not be able to leave your multiplier so high, particularly in rough air. A cyle will be induced where the aircraft will not be controllable. There are a few that are stable enough for X16, but my findings are that they are not many that will not begin a cycle in trying to hold a stable pitch attitude. Even so at X8 for a few, and rarely even X4 for a bad bird.Good luck:RTH1585368CFI

I have this problem with several aircraft (presumably all). I think it is a limitation of the FS autopilot, which controls altitude with trim. In FS, trim changes pitch, and to maintain altitude or climb, autopilot has no problem trimming pitch so nose up that a stall occurs. Several factors come into play. I think a positive feedback cycle can get started when there is a large baraometric pressure change and the ac is at or near its service ceiling. lso, CoG changes that occur with fuel burn over time. In addition I find the autopilot will not always be calibrated correctly if engaged onthe ground (during preflight) or too soon in a climb, in some cases. In these aircraft, i don't engaged autopilot until I am level at cruise and have visually verified (and thru tooltips) that the trim is where I would expect it for level flight. This helps but is no guarantee, I've returned to FSP and found terrified passengers and a ground track on the GP that shows a death spiral. Yesterday I was on autopilot in APPR mode and it suddenly trimmed the ac to 21 degrees nose up (!), putting it in a stall. I disengaged and recovered and flew the approach by hand. Moral of the story: Don't leave the cockpit. Also, I ecently got Radar Contact and it has a co-pilot that flies the plane. Haven't had the problem when he/she is "awake" and flying.Hopes this helps or at least reassures that it isn't personal :-)

"can someone explain to me why AP keeps stalling my aircraft?"One other item in addition to the good advice you've received here--make sure you set up MSFS for indicated airspeed and not true airspeed. A few members here have run into your problem where they set the autothrottle for 280kts, and started to stall at altitude. Turned out they were trying to climb at 280kts true airspeed. That's very close to stall with some aircraft. 480kts true airspeed roughly equals 280kts indicated airspeed at altitude. 280 kts true airspeed is only 160 kts or so indicated--which approaches clean stall on some of your heavier birds.It's just a thought, but highly unlikely as most folks know the difference. The suggestion for pitot heat and the one for step climbing are two more likely suggestions.Regards,John

I seem to remember reading you should not go above 4X on Autopilot, as it doesn't cope very well at those speeds. I could be wrong but....

hi guys. I have no knowledge of this Pitot heat - what is this for? sorry for dumb question.The true airspeed i have not looked into - where is FS can i change this? FSpassengers has lots of rules about the speed, i wonder if changing this setting will make fspassengers not work. I will try your suggestions.Maybe you can spot something i am doing wrong? Heathrow > gran canaria (last night) in b737-400> all lights on> taxi to runway set flaps to 15 degree > throttle to 93 percent > pull into climb at pitch 2000> was at 180 kts climb and then activated AP to get me to FL310> past 6000 turned off landing lights> past 10000 turned off strobe lights and reset the altitude indicator> then when i got to 31000 i just leave the ap on with the GPS NAV HOLD on. (no auto throttle, nothing else... dont know what everything else does and how to use it as i have self taught myself)> fly fly fly - fancy some dinner whilst on increased sim speed and left it as it was. The a/c did look as though it was climbing though and certainly wasnt as level as i usually make a prop plane. i see in some of your text that this is a sign to a stall - could you explain what is happening a little bit more so as i can try to understand this.Thanks everyone.Ande

Are you using autothrottle along with autopilot? I've noticed that in the default MSFS aircraft, if you use AP without also engaging AT, the aircraft behaves in exactly the way you describe.Also, something I've noticed when using the AP in approach mode: Sometimes it's possible to be receiving the localizer of an ILS without receiving the glideslope. You'll know this is the case if the GS is pegged in the middle when you know you've got to be under it.If you enable the approach mode at this time (while recieving a LOC signal without a GS), the AT will think you're perfectly on the GS, not realizing that you're actually not receiving the signal. When you get close enough to start receiving a GS, the needle will suddenly jump to indicate that you are below the slope, and the AT will start to fly up to re-capture it.Moral of the story: don't enable the approach mode of the AP until you're properly receiving both the LOC and the GS.

Hey Ande!Two observations!1. Never adjust your altimeter setting below 18,000ft. Once you pass the 18,000ft mark then you can change it to 29.92. This could play a little bit of a role with keeping the correct altitude and keeping the ATC goons off yoru back.2. You have to use autothrottle with the AP, especially for climbing. If you set your throttle to, let's say 75% and the aircraft is too heavy (but within limits), you could reach the point where the aircraft needs more thrust in order to achieve altitude or you will definitely experience what you are describing. If you decide not to use the AT system, then forget about the movie, the dinner, or anything else and you better keep yourself glued to the seat, "flying the aircraft", because at some point,l you will need to manually apply that extra power to reach your altitude.This whole thing is all about weight, thrust, and flying the aircraft.Hope this helps!Sincerely,Dennis D. Mullert

I agree with the gross weight suggestion. Since you have just recently transitioned from props to jets, I suspect you're carrying too much fuel. You can get away with that in a Barron, but with an airliner if you try to land with full fuel or try to climb directly to cruise before "burning off some weight,' you may crash and / or stall. http://www.graphics-free.com/animations/tr...ges/plane_6.gifAlex ChristoffN562ZBaltimore, MD

>hi guys. I have no knowledge of this Pitot heat - what is>this for? sorry for dumb question.>>The true airspeed i have not looked into - where is FS can i>change this? FSpassengers has lots of rules about the speed,>i wonder if changing this setting will make fspassengers not>work. I will try your suggestions.>>Maybe you can spot something i am doing wrong? >>Heathrow > gran canaria (last night) in b737-400>>> all lights on>> taxi to runway set flaps to 15 degree >> throttle to 93 percent >> pull into climb at pitch 2000>> was at 180 kts climb and then activated AP to get me to>FL310>> past 6000 turned off landing lights>> past 10000 turned off strobe lights and reset the altitude>indicator>> then when i got to 31000 i just leave the ap on with the GPS>NAV HOLD on. (no auto throttle, nothing else... dont know what>everything else does and how to use it as i have self taught>myself)>> fly fly fly - fancy some dinner whilst on increased sim>speed and left it as it was. The a/c did look as though it was>climbing though and certainly wasnt as level as i usually make>a prop plane. i see in some of your text that this is a sign>to a stall - could you explain what is happening a little bit>more so as i can try to understand this.>>>Thanks everyone.>>Ande > A very basic explanation: Air flow passes through the pitot tube which is then translated to the aircraft as airspeed. When the pitot tube freezes at altitude, the indicated airspeed drops on the indicator. A whole scenario of bad things happen now, especially with AP and auto thrust controls involved. To keep it short, turn on the pitot heat. There should be a pitot heat switch somewhere on the overhead or main panel. If not, use the FS default pitot heat command which you can find on the assignments pages. I can't (or won't) say positively that it is your problem, but the same scenario has happened to the best of us from this one little switch.edit: of course the weight observance already mentioned is a biggie too.