About mcp speed...

[smokeyupahead 6]

Hi guys and gals,

 

does it make sense and is it possible to set and engage a speed of 165 by pressing the mcp speed button shortly after takeoff with the autopilot off and autothrottle on while N1 is still commanding thrust?

 

I'm trying to perform the initial climbout from runway 26 at Innsbruck all the way up to the ADILO1H transition.

This is what I do:

 

"I take off by pressing the TOGA button, I notice N1 comes alive in the air and at this point I am maintaining V2 + 20.

At climb thrust I set 165 in the mcp window as per the speed restriction and then try to engage the speed button but it wont engage."

 

I can't even engage vnav on ground or in the air to have it control the speed if I wanted to try that.

As I understand N1 will not hold speed unless I use picth to control my speed in this phase.

 

I hope I was clear enough and thank you in advance.

 

Cheers,

David

[Spin737 102]

Don't touch the SPEED button.

 

I'm not sure exactly what you're trying to do, but simply changing the selected speed in the MCP should do the trick. VNAV would probably be your first choice.

 

Do you have a chart for the SID you're doing you can post? 165 seems like an odd restriction.

 

Make sure you've completed your PERF INIT and you might be able to get VNAV.

[Oliver Branaschky 2]

165 seems like an odd restriction.

 

 

165 is correct, IIRC. You gotta make sure you make that 180 degree turn in the narrow Inn valley.

 

EDIT: Yep http://charts.vacc-austria.org/LOWI/LOWI_Departure_SID 26_13122012.pdf

 

 

 

Oliver Branaschky

[Spin737 102]

VNAV sounds like the best option. Try to figure out why you can't get it running.

 

Otherwise, you'd simply need to dial in 165 from whatever your V2 was.

I can't even engage vnav on ground or in the air to have it control the speed if I wanted to try that.

As I understand N1 will not hold speed unless I use picth to control my speed in this phase.

N1 is simply giving you a constant climb power - the engines don't care what speed you want, they're just pumping out the power. You're controlling airspeed by pitch.

[Rations 102]

If your issue persists, could you post FMC and MCP screen shots?

 

Also ensure that you are inputting your takeoff runway in the FMC (or am I confusing that with LNAV requirements?).

[smokeyupahead 6]

Wow guys thanks for your replies!

Anyway I have everything setup in the fmc as it should be.

I know vnav would be my best option but I would have to fly with the autopilot on; I want to hand fly the departure with the only assistance of the autothrottle to mantain 165 knots.

I don't know if it can be done tough nor if it is a correct way of flying this departure...?

I've hit the sac already but I will post a video tomorrow.., stay tuned please.:-)

I tried to use the mcp speed mode with the ifly 737 and it worked!

My question at this point is to know which one is right.

 

Thanks again guys,

 

David

 

Don't touch the SPEED button.

 

I'm not sure exactly what you're trying to do, but simply changing the selected speed in the MCP should do the trick.

 

I tried that too but it still keeps me in the N1 mode.

[smokeyupahead 6]

 

165 is correct, IIRC. You gotta make sure you make that 180 degree turn in the narrow Inn valley.

 

Oliver Branaschky

 

There is a minimum required bank of 25 degrees. Very interesting departure, so many things going on...

[Lek767 37]

I know vnav would be my best option but I would have to fly with the autopilot on

 

No, that's incorrect. Generally, you can select an AFDS pitch or roll mode irrespective of whether the A/P is engaged or not (with A/P FLARE and ROLLOUT being obvious exceptions, but that's not important right now). In other words: you could very well select VNAV and fly the aircraft manually. In this particular scenario of the eastbound departures out of LOWI runway 26, you've got a plethora of options:

• pre-arm VNAV on the ground and set a 165 speed restriction covering the initial turn on the FMC LEGS page (if it isn't in there already as part of the SID)
  
• pre-arm VNAV, don't set an FMC speed restriction, but use SPD INTV to set a speed of 165 knots on the MCP before entering the turn, and then click SPD INTV again after exiting it to resume normal VNAV SPD mode during the climb
  
• select LVL CHG after take-off, and dial in 165 knots on the MCP, proceed through the turn, and then select flaps up manoeuvring speed and accelerate as normal (and switch to VNAV thereafter)
  
• or... technically you could stay in TOGA, select 165 knots on the MCP until you've completed the turn, and select a different pitch mode afterwards.
  

Choices, choices... They'll all do the job just fine (disclaimer: I Am Not A Pilot); which one to pick will depend on your airline's SOP or, in the case of a simmer, one's whimsical mood of the day.

[smokeyupahead 6]

I tried VNAV but unless I engage it togheter with the autopilot, the autothrottle will not hold the fmc speed of 165 knots.

Could it be because the first leg is actually a vector? Would that cause VNAV not to engage at times? Going crazy!

[Lek767 37]

I tried VNAV but unless I engage it togheter with the autopilot, the autothrottle will not hold the fmc speed of 165 knots.

 

The autothrottle will not do that because in the take-off and climb phases of the flight, unless told otherwise, the A/T is commanding a set amount of engine thrust (N1) and does not try to maintain any particular airspeed. The latter is up to you by following the flight director pitch cues on the PFD, i.e. to vary the pitch angle of the aircraft so as to achieve and maintain the desired speed of, in this case, 165 knots.

 

In order to gain a better understanding of these AFDS-related matters, I'd suggest you study FCOM Vol. 2, Chapter 4 ("Automatic Flight"). It will likely clarify a lot of the issues you're currently struggling with.

[smokeyupahead 6]

Uhm...I think I should still be able to use the mcp speed...

Let me do some other tests tomorrow, I don't want to come to conclusions yet.

 

Thank you for your help so far!

[Spook 96]

:unknw:

 

165 in the mcp - FD on - AT on. Speed selected after takeoff. Held speed regardless of what i done, pitch up or down.

 

 

 

You want to hand fly the departure. set 165 in the mcp. it may be that you cant arm LNAV/VNAV on the ground because you dont have the FD on so make sure the switch is on. If the FD is on and both nav modes are select the flight director bars will move and you have to hand fly to follow them. I took off with TOGA, gear up and hit speed.

[Captain Kevin 586]

Uhm...I think I should still be able to use the mcp speed...

Let me do some other tests tomorrow, I don't want to come to conclusions yet.

 

Thank you for your help so far!

I'm confused here. Are you trying to use VNAV or speed hold. Both do two completely different things. VNAV is going to hold your thrust and controls your speed by varying pitch. So you would have to engage the autopilot to use VNAV, otherwise VNAV wouldn't work since it controls your pitch to maintain speed.

[Spin737 102]

Autopilot is not needed for VNAV. Any mode except autoland works without the A/P.

[michal 44]

I want to hand fly the departure with the only assistance of the autothrottle to mantain 165 knots.

I heard that Boeing does not recommend use of auto throttle for manual flight. At least at some airlines what you are trying to do would go against recommended procedures.