737NG Stalls on Takeoff

[GAJ52 54]

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

[GAJ52 54]

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

[downscc 1,327]

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.

[dave_paige 11]

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

[ronzie 21]

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.

[GAJ52 54]

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

[ronzie 21]

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 :)

[GAJ52 54]

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

[Guest Devlin]

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

[ronzie 21]

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.

[Qavion 19]

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>

[Guest tomahawk_pa38]

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.

[Guest HOTELBRAVO]

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

[tunnelcat 1]

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

[wongben4 0]

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