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mcbellette

Climb speed after takeoff

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Hi all

 

I have a problem that's been plaguing me for a long time. I don't know how to get either my NGX or 777 to keep to the correct speed when climbing out of the runway. For example, in my NGX when setting up the FMC, it'll say that the speed to the first waypoint should be 150kts. So I set that on the autopilot panel, with autothrottle switched on. When I start the takeoff roll, I advance the throttles manually to about 60% and then use the clickspot that activates the computer taking over to take the throttles to the proper maximum thrust setting (e.g. 94.3% or whatever). My problem is that once airborne, the aircraft keeps on accelerating right past the 150kts to 200kts and beyond. It doesn't slow to maintain that 150kts unless I do the throttles manually from the start of the takeoff roll without autothrottle being on. How do I get the aircraft to maintain that 150kts so that I don't have to start putting my flaps up almost immediately? Can someone help me with this for the NGX and 777 please?

 

Thanks,

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In the MCP window you should put V2, or V2 + 10 depending on SOP... The rest is up to the system to control, according to many other parameters.

 

Why would you want to force a climb at such a low ( 150 KIAS ) speed anyway ?

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Some waypoints immediately after departing some airports have speed restrictions.

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look if you need to cross some waypoint at a certain speed, u should set that speed restrictions on legs page right after the waypoint.

Also...make sure you're taking off with VNAV engaged.

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Also...make sure you're taking off with VNAV engaged.

 

My RW Airline SOPs that i follow don't allow VNAV to be armed on the ground untill flaps are up! Why? Because then you have speed control at all TIMES and you know wherr your speed is so you don't go over flap limitation speed.

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How are you flying the departure, precisely? The takeoff sequence is one of the times when you have to, to use a technical phrase "do some of that pilot stuff".

 

What acceleration altitude do you have set in the FMC? Which autopilot/autothrottle modes do you have selected?

 

When you hit the TO/GA switches, look across the FMA at the top of the PFD: you should see something along the lines of:

 

THR REF | TOGA | TOGA

 

(B747 annunciations as that's what I can remember off the top of my head, but the 737 and 777 FMA is similiar). What does this mean? The first column tells us the status of the autothrottle. THR REF means that the autothrottle is commanding a "thrust reference" value: i.e. the takeoff N1/EPR that we have selected before departure.

 

The second column tells us the roll mode: TOGA. This will vary depending on various airline-specific options, but most commonly it means this will command runway heading after liftoff.

 

The third column tells us the pitch mode: again, TOGA. TOGA pitch mode will command pitch to maintain V2 + 10, or liftoff speed +10, whichever is faster.

 

When you take off, it is up to you as the pilot to rotate at Vr at the correct rate (3 degrees per second) toward the initial target attitude (about 15 degrees). Count to five -- and it is important to ignore the flight director at this stage. If you do this accurately, you should find yourself established in the climb at very close to V2 + 10 (don't forget to raise the gear!). You can now start to follow the FD.

 

The next stage is to start thinking about subsequent roll and pitch modes. If you armed LNAV and VNAV before takeoff, you should see LNAV become active at 50R. So your FMA will look like this:

 

THR REF | LNAV | TOGA

 

We now have the autothrottle commanding a specific N1/EPR setting, LNAV is giving FD commands to track the lateral route, and the pitch mode remains TOGA -- pitch to maintain V2 + 10 or liftoff speed + 10.

 

VNAV, if armed, activates at 400ft above the ground. Your FMA will now read

 

THR REF | LNAV | VNAV SPD

 

Autothrottle commanding a specific N1/EPR setting, LNAV tracking the lateral element of the route, and VNAV SPD which will command pitch to maintain the speed commanded by the FMC. During the takeoff, that will be V2 + 10 or liftoff speed + 10, whichever is faster up to the acceleration height programmed in the FMC, at which point the speed bug will increase towards 250kts, the commanded pitch attitude will reduce and the aircraft will accelerate so you can clean up.

 

The important thing to note here is that throughout the sequence, you are using pitch to control airspeed, not the thrust levers. If you don't rotate accurately and then follow the FD pitch commands, then all bets are off.

 

Also bear in mind that there is a minimum height for autopilot engagement -- probably around 250ft AGL if it's similar to the B747 -- so in any event it's up to you to fly it by hand to that point.

 

I can't envisage needing to set a speed as low as 150kts in the LEGS page: if you need to maintain V2 + 10 for longer, either set a higher acceleration altitude or use Speed Intervene.

 

On a point of pedantry:

 

 

 


make sure you're taking off with VNAV engaged.

 

You can't engage VNAV on the ground, or take off with VNAV engaged. You can arm VNAV on the ground: subtle but important difference.

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My problem is that once airborne, the aircraft keeps on accelerating right past the 150kts to 200kts and beyond. It doesn't slow to maintain that 150kts unless I do the throttles manually from the start of the takeoff roll without autothrottle being on. How do I get the aircraft to maintain that 150kts so that I don't have to start putting my flaps up almost immediately? Can someone help me with this for the NGX and 777 please?

 

Thanks,

 

 

Hello,

 

First as said earlier, you must set V2, or V2+10 (or +20) depending on the SOP as a minimum speed for takeoff and no other speed restriction until you have reached your acceleration altitude. 

If there was a speed restriction on the departure below your V2 speed then you could not comply with that restriction in any way as this is a matter of safety but I doubt this exists in the RW.

 

Then once you have lifted off from the runway, and start climbing at approx V2+10 or higher, you have to pitch up to prevent aircraft to accelerate more until you reach the acceleration altitude. At the first stage of the flight the speed is not controlled by the thrust but by the pitch.

 

Also if you feel that the plane accelerates too fast and you need a very high pitch up to maintain the speed, you may consider the takeoff and climb thrust you use.

A full thrust is generally not required for lower weights and derate thrust are usefull in this case.

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How do I get the aircraft to maintain that 150kts so that I don't have to start putting my flaps up almost immediately? Can someone help me with this for the NGX and 777 please?

 

You're expecting our planes to behave as if they're the MS default, which is not how real (large) aircraft work. As others have alluded to, the autopilot/autothrottle modes you're probably using are using pitch for speed control, based on the rated thrust for the engine. This requires you to fly the proper departure profile.

 

It's all about limits.

 

When it comes to your speed, climbing, and descending, you can set three limits:

  1. Speed
  2. Pitch (indirectly, rate of climb/descent); and
  3. Thrust

During the departure, you're most limited by your speed, and you want to gain as much altitude as possible in case an engine fails. This is why you set a rated thrust (at the T/O thrust limit for that operation), and simply climb at the max angle possible that maintains V2+10 (or as per SOP). After reaching the height of the thrust change, your thrust limit drops back to CLB, which limits your thrust further, meaning you have to decrease pitch to maintain the selected speed. After reaching the accel height, you begin to accelerate toward your flap limits, retracting flaps in the process and increasing that speed limit (VNAV automatically increases the speed bug for you - if you need to override this because of a restriction the FMC does not know about, select SPD INTV). As long as you're not nearing the altitude in the MCP ALT window, or an altitude restriction that the FMC knows about, the aircraft will assume that you will be using pitch to maintain your speed in a basic VNAV climb. In your case, it seems you're climbing at whatever pitch angle you deem appropriate and assuming the automation knows to adjust the throttles, even though you're not behaving how it's programmed to expect you to behave.

 

If you want to climb the aircraft like an MS default aircraft, you will need to use SPD (set at 150), [whatever lateral mode you want], and V/S.

 

I do doubt the assertion that there's a 150 knot limit, however. In the States, we avoid stuff like that, so much so that speeds less than 230 knots cannot be assigned to departure jets by controllers (JO 7110.65 5-7-3 d 1). Certain procedures (like those out of LGA) have a slightly lower max of (220 in LGA's case) closer in to the field, and those must be obeyed, but a controller may not assign the speed on his or her own without a procedure specifying it.

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Do a normal setup, get airborne, select FLT LVL CHG, select 150 speed. (assuming you can go that slow)

 

You would normally manoeuvre at your current flap selected retract speed above acceleration altitude.

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Some waypoints immediately after departing some airports have speed restrictions.

Please post the procedure with the 150 Kt constraint, I'd like to see that.

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Please post the procedure with the 150 Kt constraint, I'd like to see that.

 

I found 210K in the KLGA LGA5.LGA departure for runway 13, Whitestone Climb (in the text but not on the chart).  As Kyle mentioned, La Guardia has some fairly low speed restrictions. 

 

http://flightaware.com/resources/airport/LGA/DP/LA+GUARDIA+FIVE/pdf

 

However 150K is below V2 in many cases so I don't see how it could be part of any departure procedure, unless the airport is restricted to prop aircraft.

 

Mike

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My RW Airline SOPs that i follow don't allow VNAV to be armed on the ground untill flaps are up! Why? Because then you have speed control at all TIMES and you know wherr your speed is so you don't go over flap limitation speed.

 

Hum yep I see...but there are some RNAV departures...what do you then?

 

 

You can't engage VNAV on the ground, or take off with VNAV engaged. You can arm VNAV on the ground: subtle but important difference.

 

Yes sure...It engages usually at 400 FT right?

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Please post the procedure with the 150 Kt constraint, I'd like to see that.

The lowest I've found is 180 kts on some NZQN procedures: http://folhetas.com/IVAOportugal/Charts/NZQN.pdf

 

And just to offer a different technique from what's been discussed; corporate operators may do things a bit different. In the limited experience I've had with it, taking off we'd just rotate into the command bars (~9.5°) and kept it there until SOP acceleration altitude (1000' AFE). At 1000', SOP called for flaps up (above Vfs) and LVL CHG at Vy. Staying at 9.5° pitch would usually leave the jet in the Vy ballpark at 1000', making the takeoff/departure smoother for the guys in back. 

 

Although, for all of the Boeings, the technique is pretty much the same. Just stay in the command bars. TO/GA pitch mode will target MCP Speed (V2) +20 kts. When VNAV comes on at 400 AGL it will target the same. At Acceleration, you either select the vertical mode you want or let VNAV to it's thing. Doesn't need to be harder than that.

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Hum yep I see...but there are some RNAV departures...what do you then?

 

I imagine they fly them in LNAV | FLCH -- it's the horizontal aspect of the departure which is the issue with an RNAV departure really. Just have to be doubly-cautious to put the right stop altitudes in the MCP.

 

 

 


Yes sure...It engages usually at 400 FT right?

 

Precisely! 

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gpinho7, on 26 Jun 2015 - 02:24 AM, said:

 

Hum yep I see...but there are some RNAV departures...what do you then?

 

I imagine they fly them in LNAV | FLCH -- it's the horizontal aspect of the departure which is the issue with an RNAV departure really. Just have to be doubly-cautious to put the right stop altitudes in the MCP.

 

I've checked the pilots LINE TRAINING STUDENT NOTES and nothing to mention it. I will however ask him and get back!

 

Simon mentioned stop altitudes, and this airline is big on SID STOP ALTITUDES. Without taking the paragraph from my SOPs, The captain during the takeoff review items always refers to the FMC LEGS PAGE and calls out the hard altitude previously noted or inserted. He then points to the MCP ALT and confirm it matches and calls "SET"

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I just want to mention that in the 777, and I believe in the NGX,

you can use LNAV/VNAV and still hand-fly. With the A/T and FD on,

LNAV and VNAV selected or armed, Autopilot off, you follow the

FD bars. The A/T will select your predetermined TOGA thrust,

switch to the preselected Climb thrust at the pre-selected

altitude, and the FD bars will give vertical and horizontal

guidance. The A/T will switch to Speed as you approach the first

altitude restriction. The A/T will also change the target speed

as you reach acceleration altitude. So the pilot can retain

full control and still make use of RNAV/VNAV guidance and A/T

functions.

 

Mike

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Simon is right! He got back to me and mentioned all SIDs are managed the same. LNAV, LVL CHG until flaps up then VNAV.

 

All an RNAV SID is, is an SID where the points are not backed up by conventional nav aids, and you therefore need an FMC

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