TakeOff Acceleration height (BugUp) = FD commands MCP + 20

[dlh737 0]

Hello guys,Could you please confirm If the following happen to everyone or just to my config:After acceleration height (A/T TOGA mode with no Autopilot) once the BUG UP speed is selected into MCP the Flight Director commands correctly an acceleration but with a target speed of MCP speed + 20 instead of MCP speed.Any opinion about?Thanks

[bpcw001 22]

Hello guys,Could you please confirm If the following happen to everyone or just to my config:After acceleration height (A/T TOGA mode with no Autopilot) once the BUG UP speed is selected into MCP the Flight Director commands correctly an acceleration but with a target speed of MCP speed + 20 instead of MCP speed.Any opinion about?Thanks

This is how it is supposed to work.

[dlh737 0]

Ok, really thanks...my doubt rised from a previous post: http://forum.avsim.n...-after-takeoff/exactly... posts nr 9, 19 (reported below) and 20"Sylvain is right Ryan, even not selecting LVL CHG or VNAV, when at acceleration height and selecting Bug Up speed on MCP the FD should command a nose down pitch towards that selected speed. That's how it's done, it's clearly shown on FCOM and SOP's worldwide."Maybe my misunderstanding or different 737 options.

[Fabo 213]

It is my understanding, that after selecting bug up speed, 737 reverts from TOGA director mode (that would be MCP+20 with engines running, MCP with one engine out and possibly current speed if Vef is between MCP and MCP+20, but I am not sure on the last one).I am not a real 737 pilot though.

[davierosoft 13]

Takeoff RollWhen the pilot pushes a TO/GA switch on the thrust levers, these events occur:

• The FMA shows TO/GA as the active pitch mode
• The F/D pitch command shows a pitch down attitude of 10 degrees
• The F/D roll command shows a wings level attitude
• Both master lights come on to show that the F/Ds are independent
• The autothrottle engages in the takeoff thrust mode
• There is no active roll mode on the FMA.

When the airspeed is 60 knots, the F/D shows a pitch up command of 15 degrees. If an engine fails, the AC bus transfers to the good engine. The FCC on the failed engine gets the F/D commands from the unswitched FCC. The F/Ds will then show a pitch command of 12.5 degrees.In takeoff, the flight director commands show on the AIs automatically even if the flight director switches are in the OFF position. This is the pop-up mode. It occurs when these conditions are true:

• A flight director switch is not in the ON position
• The pilot pushes a TO/GA switch
• The airspeed is more than 80 knots.

The F/Ds stay in the pop-up mode for 150 seconds after the airspeed reaches 80 knots. To turn off the F/Ds while in the pop-up mode, you must set a F/D switch to the ON position and then to the OFF position.When both F/Ds are on, you can turn one off and the other stays on. Lift-OffFor a normal lift-off, the F/D goes from a 15 degree nose up command to a speed or attitude command. The initial speed target is V2 plus 20 knots. The change to speed control is a function of altitude rate.If the climb rate is less than 300 FPM, the pitch command holds the pitch attitude. For a climb rate between 300 FPM and 1200 FPM, the pitch command holds a mixture of pitch and airspeed. For a climb rate more than 1200 FPM, the pitch command holds the target airspeed.If an engine fails during takeoff, the target airspeed may change to these values:

• Failure at less than V2 - V2 is the target airspeed
• Failure between V2 and V2 plus 20 - the existing IAS is the target airspeed
• Failure at more than V2 plus 20 - there is no change to the target airspeed.

The maximum airspeed limit is the flap placard speed until the airplane reaches the MCP speed. The F/D bank angle limit is 8 degrees when the airplane is below 400 feet altitude.Ten seconds after lift-off, the speed trim engages.

[iainsmith 9]

Surely the airspeeds you mention are wrong? Should be 160 and 180 kts?Iain Smith

[dlh737 0]

So... do you think that is correct what I reported at the beginning of the post? (I always refer after Acceleration Height)

For a normal lift-off, the F/D goes from a 15 degree nose up command to a speed or attitude command. The initial speed target is V2 plus 20 knots. The change to speed control is a function of altitude rate.

If the climb rate is less than 300 FPM, the pitch command holds the pitch attitude. For a climb rate between 300 FPM and 1200 FPM, the pitch command holds a mixture of pitch and airspeed. For a climb rate more than 1200 FPM, the pitch command holds the target airspeed.

If an engine fails during takeoff, the target airspeed may change to these values:

• Failure at less than V2 - V2 is the target airspeed
• Failure between V2 and V2 plus 20 - the existing IAS is the target airspeed
• Failure at more than V2 plus 20 - there is no change to the target airspeed.

The maximum airspeed limit is the flap placard speed until the airplane reaches the MCP speed

.

The F/D bank angle limit is 8 degrees when the airplane is below 400 feet altitude.

Ten seconds after lift-off, the speed trim engages.

The maximum airspeed limit is the flap placard speed until the airplane reaches the MCP speed..... not MCP speed + 20

[Fabo 213]

Wait a minute now. So you take-off normally, then select flaps up maeuvering speed on the MCP on accel height (say 200) but FD commands 220?Do you arm VNAV prior to departure? Do you set your accel height in TO INIT page 2 in FMC?

Surely the airspeeds you mention are wrong? Should be 160 and 180 kts?

No, this behaviour refers to ground roll. Values are OK, although I wonder if with 100kt bug option, 80 changes into 100 for FD popup.

[dlh737 0]

Wait a minute now. So you take-off normally, then select flaps up maeuvering speed on the MCP on accel height (say 200) but FD commands 220?

YES... exactly what happen! The problem is only after acceleration height!

Do you arm VNAV prior to departure?

NO... What I found (as shown in my previous post nr 3)

"

Sylvain is right Ryan,

even not selecting LVL CHG or VNAV

,

when at acceleration height and selecting Bug Up speed on MCP the FD should command a nose down pitch towards that selected speed.

That's how it's done, it's clearly shown on FCOM and SOP's worldwide."

Do you set your accel height in TO INIT page 2 in FMC?

YES... I set it at 3000 ft with reduced CLB at 1500 ft like RYR Procedure

[davierosoft 13]

Surely the airspeeds you mention are wrong? Should be 160 and 180 kts?Iain Smith

Speeds are exact, we are speaking about takeoff roll, still on ground. And what you read is from the manual.

[iainsmith 9]

No, this behaviour refers to ground roll. Values are OK, although I wonder if with 100kt bug option, 80 changes into 100 for FD popup.

Ah, ok thanks for clarifying.Iain Smith

Speeds are exact, we are speaking about takeoff roll, still on ground. And what you read is from the manual.

Thanks Andrea.Iain Smith

[dlh737 0]

Any solution into SP1b?

[Tabs 2,790]

This is not wrong in SP1/1b - we had it checked numerous times in the actual airplane and a Level D sim.When you change the MCP speed (bugging up etc), the speed window and target will jump by 20 knots on the first click of the knob and then start going up normally from there. I am 100% sure this is correct, I have seen video of the real aircraft doing it.

[dlh737 0]

That's true Ryan... the procedure is fine... V2+20, the speed window jump as you mentioned...... everithing correct!What I don't understand is why if the bugup speed is set at example 220 then the FD commands to maintain 240 after acceleration height!Maybe something I'm missing?Thanks for support

[Spin737 102]

That's true Ryan... the procedure is fine... V2+20, the speed window jump as you mentioned...... everithing correct!What I don't understand is why if the bugup speed is set at example 220 then the FD commands to maintain 240 after acceleration height!Maybe something I'm missing?Thanks for support

Are you taking off with VNAV armed?