Reggaebird
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Boeing 747 Pitch Up On Touchdown

Tue Nov 10, 2009 2:05 am

I observed a Virgin Atlantic Boeing 747-400 landing at Boston Logan Airport recently and noticed a pronounced pitch up on touchdown. I reviewed other 747 landing videos and did not see the same thing. Does anyone know what causes it?

See what I am referring to here:
http://www.youtube.com/watch?v=sDVurrpvnPc
 
UAL747
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RE: Boeing 747 Pitch Up On Touchdown

Tue Nov 10, 2009 2:13 am

I believe, and I know someone will correct me, but I think when the spoilers are raised to their full position, it causes an upward pitch of the aircraft.

UAL
"Bangkok Tower, United 890 Heavy. Bangkok Tower, United 890 Heavy.....Okay, fine, we'll just turn 190 and Visual Our Way
 
XFSUgimpLB41X
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RE: Boeing 747 Pitch Up On Touchdown

Tue Nov 10, 2009 4:48 am

Spoiler deployement on touchdown, when not properly counteracted by the pilot flying, causes a pronounced pitch up.
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lowrider
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RE: Boeing 747 Pitch Up On Touchdown

Tue Nov 10, 2009 7:27 pm

The only times I have noticed it is when:
1. The outboard spoilers deploy significantly earlier than the inboard ones
2. The inboard do not deploy due to some malfunction
3. Landing with a very aft CG.
4. Conducting an autoland where the autopilot attempts to arrest the sink rate just prior to touchdown.

#'s 1 and 2 do not seem to be the case, and cause a very dramatic pitch up to the point where a tail strike is a possibility.
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pjflysfast
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RE: Boeing 747 Pitch Up On Touchdown

Tue Nov 10, 2009 10:33 pm

It appears that the elevator was manipulated to raise the nose at touchdown. Perhaps the pilot flying was trying to minimize the descent rate but just a bit too late.
 
UAL747
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RE: Boeing 747 Pitch Up On Touchdown

Wed Nov 11, 2009 2:21 am

I'm going with the spoilers, as I believe this was explained by a 747 pilot here back a few years ago. I'm also going to suggest some aerodynamic breaking as well.

UAL
"Bangkok Tower, United 890 Heavy. Bangkok Tower, United 890 Heavy.....Okay, fine, we'll just turn 190 and Visual Our Way
 
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tb727
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RE: Boeing 747 Pitch Up On Touchdown

Wed Nov 11, 2009 3:35 am



Quoting UAL747 (Reply 5):
I'm also going to suggest some aerodynamic breaking as well.

I hope not!
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point8six
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RE: Boeing 747 Pitch Up On Touchdown

Wed Nov 11, 2009 9:33 am

Have observed the pitch-up after touchdown from pilots (mainly inexperienced on type) who have continued the flare after touchdown. Aerodynamic braking is possible but not recommended due tailstrike threat.
 
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Faro
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RE: Boeing 747 Pitch Up On Touchdown

Wed Nov 11, 2009 9:46 am



Quoting Lowrider (Reply 3):
The only times I have noticed it is when:
1. The outboard spoilers deploy significantly earlier than the inboard ones
2. The inboard do not deploy due to some malfunction
3. Landing with a very aft CG.
4. Conducting an autoland where the autopilot attempts to arrest the sink rate just prior to touchdown.

#'s 1 and 2 do not seem to be the case, and cause a very dramatic pitch up to the point where a tail strike is a possibility.

Do fly-by-wire airliners like the A320 and 777 automatically compensate for pitch-up on ground spoiler deployment in the normal control law during landing?

Faro
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Reggaebird
Topic Author
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RE: Boeing 747 Pitch Up On Touchdown

Wed Nov 11, 2009 1:29 pm



Quoting Lowrider (Reply 3):
The only times I have noticed it is when:
1. The outboard spoilers deploy significantly earlier than the inboard ones
2. The inboard do not deploy due to some malfunction
3. Landing with a very aft CG.
4. Conducting an autoland where the autopilot attempts to arrest the sink rate just prior to touchdown.

#'s 1 and 2 do not seem to be the case, and cause a very dramatic pitch up to the point where a tail strike is a possibility.

What a great amount of information. Thank you so much!!!
 
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Aaron747
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RE: Boeing 747 Pitch Up On Touchdown

Wed Nov 11, 2009 5:18 pm



Quoting UAL747 (Reply 5):
I'm also going to suggest some aerodynamic breaking as well.

There was hardly any elevator input visible in the video to suggest aerodynamic braking - which isn't needed on the 747 anyway with all twelve spoiler panels deployed. Still, this video was nothing compared to the crap I've seen JAL 747 drivers pulling - massive rudder inputs before nosegear touchdown, narrowly avoided tailstrikes due to landing with all kinds of extra trim, see-saw x/wind landing touchdowns (pretty hard to do given the 74's low body gear trucks) - you name it.
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lowrider
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RE: Boeing 747 Pitch Up On Touchdown

Wed Nov 11, 2009 9:48 pm



Quoting Point8six (Reply 7):
Aerodynamic braking is possible but not recommended due tailstrike threat.

Agreed. Boeing has published data to show that aerodynamic braking is largely ineffective at pitch angles less than approx 20 degrees. Tailstikes will occur on the 74 at about 12.5 degrees, depending on conditions. It is better to get the nose down and let the brakes, reversers, and spoilers do thier job.

Quoting Faro (Reply 8):
Do fly-by-wire airliners like the A320 and 777 automatically compensate for pitch-up on ground spoiler deployment in the normal control law during landing?

I am sorry, but I don't know the answer to that, but I suspect that they do. I do not have any experience or formal training on fly by wire types, but I have been told that, in the normal mode, fly by wire systems attempt to squelch any uncommanded pitch or roll excusions.
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rampkontroler
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RE: Boeing 747 Pitch Up On Touchdown

Wed Nov 11, 2009 10:23 pm



Quoting Tb727 (Reply 6):

Quoting UAL747 (Reply 5):
I'm also going to suggest some aerodynamic breaking as well.

I hope not!

Ha ha! Good one...I caught that too!
 
flybaurlax
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RE: Boeing 747 Pitch Up On Touchdown

Thu Nov 12, 2009 12:21 am



Quoting PJFlysFast (Reply 4):
It appears that the elevator was manipulated to raise the nose at touchdown.

I see it too. I don't know why he'd do that, perhaps just accidentally pulled back a little too much? Maybe he sneezed  Wink
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tdscanuck
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RE: Boeing 747 Pitch Up On Touchdown

Thu Nov 12, 2009 6:20 am



Quoting Faro (Reply 8):
Do fly-by-wire airliners like the A320 and 777 automatically compensate for pitch-up on ground spoiler deployment in the normal control law during landing?

The web suggests that both the A320 and the 777 use C* type pitch control laws, which work on pitch rate at low speed. So, if you don't move the stick/yoke during landing, the control law will automatically reject disturbances caused by spoiler deployment.

Good info here:
http://www.skybrary.aero/index.php/Fly-By-Wire

Tom.
 
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Francoflier
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RE: Boeing 747 Pitch Up On Touchdown

Thu Nov 12, 2009 3:15 pm



Quoting FlybaurLAX (Reply 13):
I don't know why he'd do that, perhaps just accidentally pulled back a little too much?

Probably just a false impression of being about to hit the runway a bit too firmly. Even though some of the wheels had already contacted the ground, it was probably not felt in the cockpit, and the pilot thought he was still in the flare.

While the spoiler deployment normally does not generate any pitch up tendency (unless the inboards are inop), it will compound any additional back pressure applied on the yoke during touchdown.

Touching down with the thrust set above idle can also result in an undesired pitch up motion.
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