Acceleration Height

[Sean]

According to the 737 FCOM I have, during take off, first there is thrust reduction height, followed by acceleration height.

Do these typically happen at the same point?

[matta757]

I am not a professional pilot, but I believe that this depends on the specific airport.

Acceleration heights are generally governed by noise abatement procedures. Thus, they are often times higher than the thrust reduction height. I think normal thrust reduction height is 1000ft AGL. Some airports have a specified acceleration height, such as 2200ft AGL in Vienna LOWW. This is due to noise in the surrounding neighborhoods.

I am assuming optimally, acceleration and thrust reduction heights would be the same.

[MLeavy737]

Sean,
I see this alot everyday.  First thrust reduction height is just that obviously... When the power comes back to FMC computed climb setting after takeoff. Normal ops is 1000ft agl.  There is another type climb originally called ICAO-A which usually for noise abatment procedures now called something like NDAP-1 i think.  Little different climb procedure and with that you set the thrust reduction alt to 1500 and climb at a steeper angle not accelerating until 3000ft agl.  Probably other uses for it however thats all i have used it for.

Acceleration height from what i have seen involves engine out work. Our Jepps for every airport we go to is either standard engine out acceleration height of 800ft above field elevation or a specific procedure per runway that contains a specific noted acceleration altitude.  In this case acceleration altitude is where you transition from V2 and increase speed and start cleaning up airplane meaning the rest of the flaps that are still in from takeoff or go around with an engine out.

Like i said, only time I have seen acceleration altitude used  is when it pertains to engine out work.  Some airports will say something like maintain 250kts asap but thats about it, they dont call it an acceleration altitude. 

Maybe give me a line from the manual in context and i can help ya better.

Mike L

[Sean]

Thanks for the input guys.

I have delved into some other airline FCOM's I have. Low and behold, I have 3 different scenarios now!

I've pasted the After Take Off page from each...

[EDIT] At the request of Boeing Corporate the attachments have been removed. Sorry Guys. Please do not post Copyrighted materials

[MLeavy737]

Sean,
  Lol! Well ill add another one.. At Acceleration altitude call "Level Change, set top bug Flaps __" now you have 4

There all saying the same thing. Thrust reduction altitude is when the FMC computed engine power goes from Takeoff mode to Climb mode or power setting.  Sometimes thrust reduction altitude is actually a thrust increase altitude when departing with a reduced thrust power setting or flex power as some call it and climb power is actually higher. Hows that for a twist

The acceleration altitude is dealing with the transition from your takeoff climbout airspeed to the point you or the departure procedure deems it ok to start accelerating and cleaning up the airplane. Like i said, standard is 800ft AGL.  Somewhere with high terrain may be higher.  Those callouts for set top bug, set min maneuver and bug up are all the same thing.  Your setting the speed bug or MCP speed to the flaps up clean maneuver speed or the slowest speed you can/should go without the flaps extended.  This will lower the flight director bars and get you to start accelerating. Depending on the flaps you departed with, as your within 20kts of the min maneuver speed for the next flap setting and accelerating,  you can then raise the flap lever to that position.. For example if flaps up min maneuvering speed is 210 kts, as you reaching 190kts you would call "Flaps Up, after takeoff checklist" the way we do it anyhow..

My suggestion while you have those manuals is to look over the takeoff profiles, they will break down every segment, reason, and callout for every phase of departure. Then look over flap extension and retraction procedures.. I dont think many people realize that its not just setting/retracting flaps at a certain airspeed like a 172 or something..  737's for any flap setting has a 20-30 kt range of usability and the procedures are extremely different when accelerating to and decelerating into a particular flap range..

Look into those a little then the acceleration altitude reason and procedure itself will make alot more sense.. Have fun!

Mike L

[Maurice]

Thank you Mike. This was a very useful explanation for questions that always intrigued me.
I do have one more question for you though. What you said made perfect sense but what about if you engaged the A/T and hit the TOGA switch during the takeoff run?

Since you are no longer controlling the power, does the flight director react to inputs from the FMC rather than from the MCP speed setting?

I hope my question makes sense.

EDIT: does VNAV need to be armed to enable the fight director to follow the FMC settings?

Thanks,
Maurice

[MLeavy737]

Maurice,
  Just curious... How do you takeoff in your sim? What you said is exactly the way your supposed to do it!

On our before takeoff checklist, which is completed basically when number one at runway, you arm the autothrottles.  When on the runway and cleared.. First bring power up to 40% to let them stabalize.  Now start bringing power up.. At about 70% hit the TOGA switches.. The autothrottles will engage and drive the power up to takeoff setting on FMC page. Forget what page exactly but the quick way to get there is hit INIT REF, NEXT 2 times Takeoff page 3 i guess.. Anyhow, power goes up then the Flight Mode Annincuator should say THR HOLD i believe.  That means power is holding that takeoff N1 from FMC.  So thats power...

The flight director during takeoff is another thing.. I would have to get the books out for this exactly but from what i remember.. The first 400 ft the FD is giving you a 12degree initial pitch.. After 400 ft it should be giving you a v2 to v2+15 climb speed until a mode is selected on the MCP.  Thats why at 800 ft our call is " level change, set top bug" thats put the FD pitch into MCP speed mode, setting top bug or about 210 kts will lower FD pitch bars and start tou accelerating.. Thats when you start cleaning up airplane like i said before. 

Also with VNAV like you asked.. The only mode on MCP that can be armed for takeoff  on the ground is LNAV.  Or i should say should.  Never tried nor should try anything else.  So a VNAV climb is just another climb you can do after takeoff.  We call them L2 or L3 climbs. So instead of LVL Ch top bug you just call " VNAV, Flaps 1" that will bring speed bug to whatever type climb you put in and lower FD pitch to obtain that speed.. Now clean up on schedule. 

Acceleration height is basically what altitude you hit LVL CH or VNAV.. 

Got it? Lol.. Ill just have to come over one day and show ya!

Mike L

[Sean]

This is the info I'm after!

When you say "set bug-up speed", do you mean simply look at the ASI and set the MCP speed to the speed adjacent the green UP bug?

[MLeavy737]

This is the info I'm after!

When you say "set bug-up speed", do you mean simply look at the ASI and set the MCP speed to the speed adjacent the green UP bug?

Yes exactly.  In NG's that will be somewhere around 210-220 kts.  Just set the MCP speed on top of that bug which will be the "top bug"

Mike L

[Sean]

Excellent. Thanks Mike.

Another question...

Why not set the MCP speed to 250kts so you can start accelerating towards that, rather than having to look at the speed tape for the bug up speed?

[Maurice]

Maurice,
  Just curious... How do you takeoff in your sim? What you said is exactly the way your supposed to do it!
......
....
Got it? Lol.. Ill just have to come over one day and show ya!

Mike L

Hi Mike,

If I have a route programmed on the FMC, before takeoff, I arm A/T, LNAV and VNAV. During the takeoff run, I engage the A/T as you mentioned and I just follow the flight director until I get tired of flying manually and engage the A/P. This works quite well for me but I often run into difficulties if I have not programmed a route and I am just doing a quick manual flight.

Things then seem to happen too fast and I often either end up with a very low speed because of a too steep climb or the plane accelerates too fast and I get the flap over speed warning because I did not retract the flaps on schedule. Basically I get confused and/or rushed about what to do when and I really need a co-pilot  .

Too bad your airline does not fly to Toronto otherwise I would kidnap you for a day and pick your brain 

Thanks for the great explanations.

Maurice

[Sean]

Basically I get confused and/or rushed about what to do when and I really need a co-pilot 

That's my problem. The take off and initial climb phases are very rushed!

[Speedbird17]

Derate 2 or load it up with Pax and fuel. Slows me down considerably!!


Sent from my iPad using Tapatalk HD

[MLeavy737]

Excellent. Thanks Mike.

Another question...

Why not set the MCP speed to 250kts so you can start accelerating towards that, rather than having to look at the speed tape for the bug up speed?

Sean,
  As you know when you fly airplanes you want to be 1 step ahead and not any more than that lol. Setting 250 is like setting a speed where your skipping the whole takeoff and initial climb phase and going right to climbout phase the way i see it anyhow. Most importantly however is the actual speed thats set for takeoff and that MCP speed is set for V2.. We all know what that speed is for would you want to be trying to handle a engine loss at V1 and have to reach up and set the MCP speed to V2, assuming you remember what its supposed to be having it set for takeoff assures its already there and now you just pitch up and hold that speed.. Nice and easy!

Mike L

[MLeavy737]

Maurice,
  Just curious... How do you takeoff in your sim? What you said is exactly the way your supposed to do it!
......
....
Got it? Lol.. Ill just have to come over one day and show ya!

Mike L

Hi Mike,

If I have a route programmed on the FMC, before takeoff, I arm A/T, LNAV and VNAV. During the takeoff run, I engage the A/T as you mentioned and I just follow the flight director until I get tired of flying manually and engage the A/P. This works quite well for me but I often run into difficulties if I have not programmed a route and I am just doing a quick manual flight.

Things then seem to happen too fast and I often either end up with a very low speed because of a too steep climb or the plane accelerates too fast and I get the flap over speed warning because I did not retract the flaps on schedule. Basically I get confused and/or rushed about what to do when and I really need a co-pilot  .

Too bad your airline does not fly to Toronto otherwise I would kidnap you for a day and pick your brain 

Thanks for the great explanations.

Maurice

Maurice,
  I think if you have VNAV engaged for takeoff, when you hit TOGA it should come out of VNAV and into TOGA mode? Supposed to anyhow i believe.. Never tried it on takeoff though in the real one.

Also sounds like you need to derate the engines a little in the FMC if thats possible with what your using. Also add some fuel and weight like it was mentioned here. I have done max power takeoffs in a 737-900 with no passengers and light fuel and i know the feeling your talking about.  The acceleration was unreal and with 20deg nose up the airplane just wanted to accelerate and go. The flap and MCP selection calls just rolled out in one sentence lol.. Its tough. 

98 percent of our takeoffs are derated for engine life and passenger comfort. Were supposed to initially pitch to command bars then up to 20deg to maintain V2+15 unitil acceleration height. If your light and full power yes its rushed for everyone! With proper reduced engine figures it flows very nice.. Smooth rotation to about the bars or a little more sometimes 16-17 deg will have your speed sitting right at V2 +15.. If you delay your rotation or are slow about it your speed will be a little faster and youll have to increase pitch a little more..

Ill just have to show you sometime! I look forward to it someday!

Mike L

[fsaviator]

This thread is really great guys, thanks!

As for keeping up with the plane...  we should all also remember that we are all flying an airplane using procedures that are normally set to be done with two pilots.  I have found that I usually need to add about 15-20% more time and distance to accomplish everything by the book.  Otherwise I end up skipping over things that don't seem as important in an airplane that isn't actually thousands of feet in the air

On the other hand, as was evident at FDS last month.  I spend most of my time flying alone, so when I'm actually sharing a cockpit, CRM goes out the window and I have a hard time keeping up (especially when not using checklists).

Mike, thanks for keeping us straight!

Can't wait for to find a house and get my sim up and running.

Warren

[MLeavy737]

This thread is really great guys, thanks!

As for keeping up with the plane...  we should all also remember that we are all flying an airplane using procedures that are normally set to be done with two pilots.  I have found that I usually need to add about 15-20% more time and distance to accomplish everything by the book.  Otherwise I end up skipping over things that don't seem as important in an airplane that isn't actually thousands of feet in the air

On the other hand, as was evident at FDS last month.  I spend most of my time flying alone, so when I'm actually sharing a cockpit, CRM goes out the window and I have a hard time keeping up (especially when not using checklists).

Also same goes with the flight profiles.. Combine the calls withe the flows and flying and your golden

Good luck!

Mike, thanks for keeping us straight!

Can't wait for to find a house and get my sim up and running.

Warren

No problem Warren Hey one thing that may help you and others that feel like they get behind when flying solo while using checklists is to really study and learn flows.  Pick a good flight manual and break down every flow and learn it so that you can do it without even thinking about it.  Thats one of the first things i learned coming to the airlines. You had to know your flows and callouts big time!  I believe theres a CAL flight manual on the internet somewhere and i dont think the 737 flows have changed much. Go to section 3 and anywhere there is a flow diagram for a phase write down the steps and learn it! You will find flying and checklists use easy after that.. Probably wont even need the checklist and remember a checklist is a "check"list. No a do list.. Thats why there are flows.

One of these days ill make a checklist or a flow list based on my stuff maybe give em out at the next sim meet as we all fly together!

Mike L.