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GAJ52

737NG Stalls on Takeoff

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I have come back to the PMDG737-800 after flying the RFP747-200 for a bit. I have quickly got back into flying with an FMS again and generally have no problems apart from one... During takeoff I activate the autothrotte and use the TOGA to initiate power (all works ok), after I rotate at about 400 ft I select A autopilot to CMD the V2 increases by 20 kts and the N1 and LVL CHG switches both light up as normal, but the engines reduce power and start hunting at around 60 to 70 % with the result I begin to stall.I have rechecked all the settings making sure I have activated the FMS and A/T, F/D. Any idea what I might be doing wrong ??BTW this also happens if I select VNAV at around 1000 Ft.Glen

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I have just tried another takeoff using the autothrottle and TOGA mode again all went well, 'THR HLD' annunciated at 80 kts and the engine N1 was about 94% then as the copilot said rotate the engines reduced to about 60% with the speed light coming on, before I could cancel the autothrottle I hit the deck !!Glen

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This happens almost everytime I fly a sequential route... but has never happened on a fresh flight. You didn't mention if you were on a second leg... ? I assume your alternators are on line, which is required for A/T.

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Strange, I have never had that happen either on a fresh start or on a continuation flight.

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I assume your MCP settings were correct at roughly 200 knots and at least 3000 feet above ground.In the FMC have you set the N1 performance parameters? It would not hurt to check your cost index as well.Make sure all of your fuel pumps are on for TO and I believe some center tank fuel is required for TO.I always wait until at least 1000 AGL before engaging CMD.If you haved the throttle quad displayed, do you see them retarding when this happens? If so, I kill the A/P switch and ride the throttles manually until stable and high enough to engage it again.When engaging A/P the PDF should announce I believe N1 climb. VNAV should not be used until climb at 3000 AGL is established. This is because sometimes VNAV does not kick in on the first try asnd you need some room to disengage and reengage it.In the cockpit videos I have, the PF or PNF always has hands ready on the power levers until climb is stabilized a few thousand AGL with CMD ON so they can be manually increased if something fouls up.

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I think I may have found the reason for my original problem.When setting takeoff power I would increase thrust using my Saitek X52 throttle to 40% N1 then press the TOGA button but would leave the Saitek throttle at the 40% setting. If after pressing the TOGA button I then increase the throttle to full thrust the engines then behaves normally on takeoff and maintains the desired climb speed.I wrongly assumed the auto throttle ignored the position of my X52 throttle once it was activated.Glen

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I'd have to look it up but something happens to AP or AT after reaching 80 knots which is why there is a call-out.At some point if manually retarding or increasing the power levers they override AT as I recall. I should brush up on power handling from a manual perspective :)

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I've just had a look in the manual for Takeoff Procedures Page 5-9 of the Normal Procedures section - a copy printed belowTakeoff Procedure Explained:Advance thrust levers to approximately 40% N1.Observe engine instruments stabilized and normal.Push TO/GA switch to advance the thrust levers to takeoff N1.Verify mode annunciation.Note: After takeoff thrust is set, the captain

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Ahh, now that explains a lot, I have been using vertical speed on take-off because LVL change caused a stall,I will try this next time.ThanksAndrew

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TOGA will engage N1 full and best climb rate. LVLCH should not be used for takeoff until your safely above ground in a stable climb and CMD is armed at which time speed is engaged and HDG. For a missed approach if on a VOR or LOC, as soon as you are locked to the LOC adjust the HDG to the indicated missed approach heading and ALT also as spercified in case you perform the TOGA procedure.

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PMDG and many other high end sims are like this BY DESIGN (Isn't it mentioned in the manuals/tutorials somewhere?)When the A/T goes into HOLD mode (real aircraft) at the specified speed (for your particular aircraft), A/T servomotor power is removed allowing the pilot to position the throttles, manually, anywhere he wants to (without fighting the A/T servomotor). He/She may want to do this for a rejected takeoff or to remove derates if extra power is needed for abnormal conditions. If you don't have your joystick throttle properly positioned (fully forward or aligned with the takeoff target thrust level), the sim may see your 60% throttle setting as a manual command to retard the thrust to that power setting.Because joystick throttles don't usually have servomotors to drive the lever to where they should be after TO has been pressed, you have to move your joystick lever manually to the TO target thrust (or simply firewall it).BTW, this has been mentioned many, many times on this forum and other forums ;)Cheers.Q>

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I find that where the throttle is manually positioned doesn't make any difference once past 80kts if I have selected TOGA - takes off fine. You have put the correct speed (V2) in the speed box haven't you ? because when you select the A/P it will auto add 20kts to it as the safe climb out speed.

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Hello to allWhat Glen described about the throttle lever position is exactly what i recognised also with the PMDG 747. I use a Saitek X-52 as well..If i press TO/GA and let the throttle at about 40% the thrust reduces when passing 80 knots!If i set full or almost full power on the hardware after pressing TO/GA all works perfect.This behavior should be linked to the option "override AT by throttles" (there is something like that) in the PMDG-Menu. Maybe thats the reason some have this problem and some doesn't..Pleas correct me if i'm wrong.Best regardsDaniel

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Hi all pilots,This problem has plagued me as well, but usually with the PMDG 747. It's definitely related to the A/T and A/P override option in the PMDG menu. If your controller has a little bit of noise and has no dead zone set, the aircraft seems to interpret the noise as a small throttle input and will disengage the A/T for one or more engines. The same problem will occur with the A/P, a partial disconnect of one function with the A/P no longer following a particular MCP command. You will NOT get a warning horn when this occurs with either system, so you won't know that it has occurred until something behaves strangely, i.e. you stall.I was tearing my hair out trying to figure why I was having problems with the A/T and A/P not following commands partway into a flight until I stumbled across this little quirk. It may not be as realistic, but I unchecked both of those options in the PMDG menu for both the 737 and 747. You might want to try setting a larger dead zone in the sensitivities option for the throttle on your stick and see if the problem reoccurs for your situation.I always set my throttles to 70% N1 before engaging TOGA mode with the A/T armed to be sure I get a full throttle response.Kim

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Hi, talking about servomotors... does anyone know where I can get a sim throttles with servomotors... it is like the pain in my A** everytime when I disengage the auto throttles for landing... you know... unlike airbus in which there is a donut on the EPR or N1 display so that people can align the throttles levers first before disengage the A/T...However, for PMDG 747 (or other Boing SIM products) I have no idea where exactly I should adjust the levers to the A/T determined thrust, and end up being either overpowered or underpowered....Could anyone give me some advices on it...cheers,ben

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Sim-Throttles with servomotors ?. I don't know if such a thing is in the market. But if exists it must be rather expensive I'm afraid !I agree with you that disconnecting the A/T on final appch can be a nightmare sometimes. But think (talking about the 744) that if you had set 70% N1 before pushing TOGA, and you don't touch again the throttles until you are well stablished on the Glideslope (with full flap and gear down), the typical N1 value in that phase will be around 65-70% in most of the cases, so, the throttle dissalignement wil be very slight.When flying the 737, I set 40%N1 to stab the engines, then I advance the throttles to 65% and inmediately after I push TOGA. This way, I make sure that my throttles will be at 65% when I disconnect the A/T before touchdown.Jose Luis.

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Why are you disengaging the A/T for landing?If I use the Autothrottle for the whole flight, I push my joystick fully forward immediately after I push the TOGA switch(screw) and pull it fully aft a few moments before Top Of Descent. The only other time I would touch the throttle lever is during Go Around (similar to TO) or if I am flying manually.Cheers.Q>

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Hi Q, Yeah.. I do the same thing as well.. except for landing... when I am about 500 AGL, I usually disengage everything and land it manually like a pro...and sometime during gusting condition, I need to make minor adjustment with the power in order to stay in the glide path and maintain the speed(or 2 red 2 yellow for PAPI) and that's the time when everything screws up...for example... the A/T is at 68%N1 and the lever is on 80% N1, even with A/T disengeged,the power will remain at 68% as long as I don't touch the lever.... However, the problem pop up when I want to give the 747 some power... I move the lever forward and hope to get around 75% N1, and the position of the lever is orginally at 80%... guess what.. I move the throttle a little bit and I get 90%N1... and the nose pitchs up and the approach is screwed....BADI am still thinking what is the best solution to this problem.....Ben

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>Why are you disengaging the A/T for landing?>Cheers.>Q> Well, because I am not flying an Airbus...and also because I don't like autolands.I normally disengage the A/P before and the A/T after. This way I take pitch and roll control while the A/T still controls the speed. And finally I disconnect the A/T for the very last phase of flight.Jose Luis.

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I think you are experiencing USB port stepping. Without AT on, see if your throttle levers on the panel are jumping. In addition, your sensitivity may be quite high and throttles in that range can put out course settings. When you initially move the throttle after disengaging AT indeed it seems necessary to get a significant change in order for the controller movement to be recognized.If I am going to control power manually I usually start by the OM to get the aircraft configured for the power on the slope to avoid this issue.One other brief issue that has been mentioned by others and experienced by me is that on the AP CMD master disconnect, I lose the throttle sync between engines with my single control lever now controlling only one engine. I have a fully registered FSUIPC and have mapped a key-combo to a throttle sync function to restore both engine control. I found this out when popping the AP disconnect just before the threshold and having trouble with the retard results and then difficulty with steering off the runway due to asymmetrical thrust.

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As I recall (not 100% sure) the registred version of FSUIPC has a function to remove/limit joystick-noise/spikes. Normally in FSX I don't experience any noise/spikes but during TO (Level-D B767) I've once experienced that the Autobrake kicked in (RTO) because the sim "thought" I had reduced thrust (becase I failed to move the throttle leveler when I hit N1 on the MCP). Since I've made it a habbit of moving the throttle leveler to Max when I hit N1 (for the take off) and once I start my descent (when the FMC commands Idle thurst) I fully cuts throttle input - since duing this I've never experienced any problems.[link:fs2crew.com]http://fs2crew.com/betateam.jpgPelle F. S. Liljendal

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"Well, because I am not flying an Airbus"Sorry, I'm not familiar with Airbuses... What has flying an Airbus have to do with disengaging the A/T?Thanks.Cheers.Q>

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>>Sorry, I'm not familiar with Airbuses... What has flying an>Airbus have to do with disengaging the A/T?>Q>Well, as far as I know, the standard Airbus A/T (they call it AUTOTHRUST, not autothrottle) procedure is:1.- TAKEOFF: Advance the thrust levers to takeoff position as calculated (TOGA or FLEX).2.- INITIAL CLIMB: At aprox 1500 ft AGL retard the levers to the CLIMB position, where they will be for the whole flight. The levers will not move as they have not servos, and the FADEC system manages the appropriate thrust.3.- LANDING: On very short final (if not performing an autoland), at 20 feet radio-altitude a callout announces: RETARD, RETARD !!4.- Inmediately the pilot brings the levers to IDLE and this action disconnects the A/T.So, in this procedure there is not a direct A/T disconnecting action, they normally use the A/T for the 100% of the flight.Jose Luis.

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I would Beg to differ in a couple ways.During Many, Many, Many landings, the approaches are handflown, and the throttles commanded by hand. the only thing that would really permit the A/T controlling the throttles all the way down, is an Autoland. The simple reason for this is, The airplane doesnt know what the pilot wants to do, thrust management during a handflown is much much better controlled by the PF.RETARD is only anounced at 20 feet IF the throttles are not already at idle. if the throttles are at idle. the bus' says nothing. Because the airplane tells the pilot to retard the throttles, doesn't mean he should or needs to think of it as a "Reminder". Commonly while flying to Denver international in colorado in the summer, due to the heat and altitude. throttles aren't pulled to idle untill around 5 feet or so, the airplane needs the extra thrust.They normally use the A/T most of the flight, just like a Boeing pilot would.

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>>thrust management during a handflown is much much better controlled>by the PF.>Sometime ago I remember reading some real world Airbus manuals that encouraged pilots not to disconnect the A/T even when hand flying. And the reason they gave -more or less- was that the FADEC (Full Authority Digital Engine Control) would care of speed and thrust much better than any human pilot. Jose Luis.

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