krisyyz
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Boeing 777 Autopilot And LNAV/VNAV On To

Thu Jan 14, 2010 4:31 pm

Hello.

I have a few questions about the B777s autopilot’s use during take off and the climb. I would really appreciate some information. I was watching the JustPlanes Air Canada 777 video. The Captain flew the aircraft up to FL220 before turning on the AP. I know that LNAV and VNAV are engaged prior to take off so the FD can project the computed route and angle of climb on the PFD. Is the PIC in total manual control until AP is engaged? Or does VNAV or LNAV help the pilot maintain the correct flight path? The Captain seemed to be making very minor inputs on the yoke yet the plane was constantly changing pitch and roll angles prior to engagement of the AP.

If the AP in not engaged and there is a change is heading or a speed intervene, is that information merely reflected on the FD cross or does it have any direct influence on the flight controls.

I know that the B777 has one of the most advanced flight control systems and is easy to fly when compared to the B767. I guess I was just surprised at the ease of the pilots while in control of this massive aircraft.

I hope I have explained my question clearly. My thanks in advance for any contribution to this topic.


KrisYYZ
 
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Jetlagged
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Thu Jan 14, 2010 8:27 pm

Without AP engaged the pilot would be in full manual control, following the FD commands. Only small control movements are necessary for normal airline flying, outside of takeoff and landing phases. This limits the rates of pitch and roll and reduces passenger discomfort. For example, a small roll input simply means the aircraft will take longer to achieve the desired roll angle, it doesn't affect the angle finally reached. So it's quite possible that the control inputs the crew used are barely perceptible in the video.

Although the 777 has an advanced (FBW) control system compared to the 767 from the pilot's point of view manual flying is very similar. Within the flight envelope, FBW merely improves the handling qualities.
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XFSUgimpLB41X
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Thu Jan 14, 2010 8:36 pm

Quoting Krisyyz (Thread starter):
I know that LNAV and VNAV are engaged prior to take off so the FD can project the computed route and angle of climb on the PFD. Is the PIC in total manual control until AP is engaged?

The PF (pilot flying... it can be the PIC or SIC) is in total manual control of the aircraft until the AP is engaged. Whatever inputs you send to the controls will happen. edit: There are certain stall protections that may be involved in certain aircraft. Under normal flight regimes what you send through the yoke or stick will be what is reflected on the response of the aircraft.

Quoting Krisyyz (Thread starter):
Or does VNAV or LNAV help the pilot maintain the correct flight path?

LNAV and VNAV are simply the modes that the flight director is in when the AP is off, or when the AP comes on- it will be in those modes. The flight director reflects the "suggested" pitch and roll commands for the pilot flying to take. It is up to you if you want to follow its suggested actions. Most times you can simply follow it- there are other times where you want to aviate a bit more, if you will. We call that "looking through the FD."

Quoting Krisyyz (Thread starter):
If the AP in not engaged and there is a change is heading or a speed intervene, is that information merely reflected on the FD cross or does it have any direct influence on the flight controls.

If there is a change in heading, the PF would direct the PM to change the lateral mode to "heading select" or the speed change as necessary. The flight director would reflect the suggested pitch and roll changes to complete that action. It is up to the PF to manually move the controls, though.  

Always remember- even when the AP is engaged, the PF is still "flying" the plane, just not the grunt work of moving hte controls. You always stay connected with what the AP is doing and make it do what you want it to do, not the other way around.

Quoting Krisyyz (Thread starter):
I know that the B777 has one of the most advanced flight control systems and is easy to fly when compared to the B767. I guess I was just surprised at the ease of the pilots while in control of this massive aircraft.

Heck, the 767 is extremely light on the controls. I've never flown the 777, but the 767 is so light on the controls it's almost twitchy!

[Edited 2010-01-14 12:39:00]
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tdscanuck
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Fri Jan 15, 2010 12:51 am



Quoting Krisyyz (Thread starter):
Is the PIC in total manual control until AP is engaged?

In the sense that they control the plane's response, yes. Since the 777 is full FBW, the flight control computers are always in the loop (a separate function from autopilot and FD). There's not really any such thing as "total manual control" on a FBW airliner.

Quoting Krisyyz (Thread starter):
If the AP in not engaged and there is a change is heading or a speed intervene, is that information merely reflected on the FD cross or does it have any direct influence on the flight controls.

Just on the FD. With AP disengaged, the AP & FMC have no connection to the flight controls.

Quoting XFSUgimpLB41X (Reply 2):
Under normal flight regimes what you send through the yoke or stick will be what is reflected on the response of the aircraft.

This wording is key...the pilot is in control of the *response* of the aircraft, not the individual control surfaces. The FBW system will move the surfaces whichever way it needs to to obtain the response that the pilot has commanded.

Tom.
 
cobra27
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Fri Jan 15, 2010 1:35 pm

Lnav and Vnav engaged at takeoff run, possibly just light on, but no autopilot swith on?
Don't they turn on autopilots at 200 or so feet when the aircraft is stabilized?
Never heard of autopilot takeoff before.
 
XFSUgimpLB41X
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Fri Jan 15, 2010 11:52 pm



Quoting Cobra27 (Reply 4):
Lnav and Vnav engaged at takeoff run, possibly just light on, but no autopilot swith on?
Don't they turn on autopilots at 200 or so feet when the aircraft is stabilized?
Never heard of autopilot takeoff before.

The flight director is in TO/TO for takeoff roll.... LNAV and VNAV may be armed, but are not active.

LNAV becomes active around 100 feet, VNAV becomes active at climb thrust reduction.


The autopilot may be engaged as low as 200 feet, however is typically not engaged until 18,000 feet.
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tdscanuck
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Sat Jan 16, 2010 12:54 am



Quoting Cobra27 (Reply 4):
Lnav and Vnav engaged at takeoff run, possibly just light on, but no autopilot swith on?

LNAV and VNAV are FMC, not autopilot, modes. They can be armed at takeoff, in which case they'll take over driving the Flight Director when they engage. The FMC modes command both the FD and the autopilot...you can use all the FMC features without ever using the autopilot.

Quoting Cobra27 (Reply 4):
Don't they turn on autopilots at 200 or so feet when the aircraft is stabilized?

You can, but you don't have to.

Quoting Cobra27 (Reply 4):
Never heard of autopilot takeoff before.

That's because there isn't one. Takeoff is still the only flight phase you can't use autopilot.

Quoting XFSUgimpLB41X (Reply 5):
The flight director is in TO/TO for takeoff roll....

TO/GA and TO/GA, I think.

Tom.
 
XFSUgimpLB41X
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Sat Jan 16, 2010 2:26 am



Quoting Tdscanuck (Reply 6):
That's because there isn't one. Takeoff is still the only flight phase you can't use autopilot.

Don't forget taxi, too.  Big grin

Quoting Tdscanuck (Reply 6):
TO/GA and TO/GA, I think.

Ah... another point where the 777 logic and 767/757 logic differ slightly then. Same idea and result.  Smile
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cobra27
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Sat Jan 16, 2010 12:26 pm



Quoting XFSUgimpLB41X (Reply 5):

The autopilot may be engaged as low as 200 feet, however is typically not engaged until 18,000 feet.

Are you sure. I always thought that turning on VNAV at around 200 ft is company policy to save fuel?
 
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ThrottleHold
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Sat Jan 16, 2010 4:30 pm



Quoting Cobra27 (Reply 8):
Are you sure. I always thought that turning on VNAV at around 200 ft is company policy to save fuel?

You're confusng the autopilot with the FMC modes. VNAV can be engaged, but that doesn't mean that the autopilot is too.
 
cobra27
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Tue Jan 19, 2010 11:42 am

I know that FD gives guidance but Autopilot is much more precise. I think that my at Adria (small airline in my country) uses autopilots ASAP and i heard often it is actually de facto at Ryanair
 
Lemmy
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Tue Jan 19, 2010 5:26 pm



Quoting XFSUgimpLB41X (Reply 2):
there are other times where you want to aviate a bit more, if you will. We call that "looking through the FD."

Interesting. Can you give an example of what this might look like?

Also, when do you normally turn the FD off? I assume that, if you're hand-flying and no longer following your programmed flight plan (in the traffic pattern, maybe?), you'd want to get rid of the FD guidance, since it's not valid.
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XFSUgimpLB41X
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Tue Jan 19, 2010 7:46 pm



Quoting Lemmy (Reply 11):
Interesting. Can you give an example of what this might look like?

It's simple! Just ignoring the FD commands, haha.

Quoting Lemmy (Reply 11):
Also, when do you normally turn the FD off? I assume that, if you're hand-flying and no longer following your programmed flight plan (in the traffic pattern, maybe?), you'd want to get rid of the FD guidance, since it's not valid.

Sometimes I never turn it off... but, typically for any visual pattern I'll turn it off. "Looking through" it that much and having the other guy try to synch it up to what you're wanting to do is too much work. Turn it off and fly!
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aviopic
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Tue Jan 19, 2010 9:39 pm

Quoting Tdscanuck (Reply 6):
That's because there isn't one. Takeoff is still the only flight phase you can't use autopilot.

Although not certified to perform a fully AP T/O it will work on the F70/100.
Engage ATS which usually done before T/O anyway.(edit)
Dial in a speed(doesn't matter what but something well above rotation speed is advised   ) on the flight mode panel, engage AP, pull the ToGa trigger and off you go.
During the roll down the runway dial in some altitude on FMP and press Level Change at rotation speed.
At an altitude of 30Ft(the legal AP engage alt) the second AP will come on automatically as the a/c senses a critical flight phase as it would do during approach for an autoland.
No problem really.

[Edited 2010-01-19 13:46:09]
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tdscanuck
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Wed Jan 20, 2010 2:32 am



Quoting Lemmy (Reply 11):
I assume that, if you're hand-flying and no longer following your programmed flight plan (in the traffic pattern, maybe?)

Even if you're in the pattern, you may be under ATC control with vectors. In that situation, you might want to use the FD even though you're flying manual (the PNF would be driving the mode control panel to keep the FD plan in sync with ATC direction). And, if you're flying the ILS, the FD takes over as your primary cue for tracking the ILS beam.

Quoting Aviopic (Reply 13):
Although not certified to perform a fully AP T/O it will work on the F70/100.

Good point...I amend my statement to "takeoff is still the only phase of flight that you're not supposed to use autopilot."!

Tom.
 
CX Flyboy
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RE: Boeing 777 Autopilot And LNAV/VNAV On To

Sat Jan 23, 2010 12:21 am

The only time we do not use the FD is if the FD cannot give us accurate tracking information which is the case when on a visual approach with no approach guidance, or in the final segment of a VOR or RNAV approach where there is no accurate profile guidance right down to a runway crossing fix.

In 99% of all cases, we fly with the FD on, giving us guidance from the modes and selections on the MCP panel or the VNAV or ILS, LNAV or LOC modes. We can also fly with them off for departure for training purposes but this is unusual.

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