Soxfan
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Effect Of Wake Turbulence On Aircraft On Ground

Tue Mar 08, 2011 2:54 am

I've heard ground control telling aircraft taxiing behind large planes "caution wake turbulence." Can wake turbulence really push a plane around on the ground? Or, is it like a code for the second aircraft to maintain a certain distance behind the larger plane?
Pilot: "Request push, which way should we face?" JFK Ground: "You better face the front, sir, or you'll scare the pax!"
 
Mir
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Tue Mar 08, 2011 3:12 am

No, wake turbulence is not a factor on the ground - it's only created when an airplane is in the air. ATC only mentions it if the aircraft will be taking off behind the larger aircraft, meaning that the pilots will have to worry about it at that point.

-Mir
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26point2
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Tue Mar 08, 2011 3:37 am

I have wondered this too. I suspect they mean to say "caution jet blast" while on the ground but for whatever reason they say "caution wake turbulence". Of course there is no wake turbulence until the wing is producing lift.
 
ThirtyEcho
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Tue Mar 08, 2011 4:52 am

Airborne helicopters can pose a hazard to taxiing light aircraft on the ground.
 
jetboy757
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Tue Mar 08, 2011 8:40 am

The definition of Wake Turbulence in the pilot/controller glossary...

WAKE TURBULENCE- Phenomena resulting from
the passage of an aircraft through the atmosphere.
The term includes vortices, thrust stream turbulence,
jet blast, jet wash, propeller wash, and rotor wash
both on the ground and in the air.

Therefore when I am working ground control i say "caution wake turbulence" because it includes all types and is much easier to use the same phrase all the time instead of having to think if you're saying the right thing for the right type of aircraft.

That being said i've seen a situation where a FedEx MD-11 taxied down a runway while a caravan was landing on the parallel because the taxiway was blocked. The caravan started to rock back and forth prior to touchdown as it passed the FedEx. Also, a heavy jet making a 90 degree turn did flip over a cessna that was parked on the ramp at my airport.

When a controller says "caution wake turbulence" it's a legal cover so in the event that something happens the FAA can say that they were warned. It is not a code with a set amount of distance, it's just a heads up to the pilot.

[Edited 2011-03-08 00:43:22]

[Edited 2011-03-08 00:54:39]
 
oly720man
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Tue Mar 08, 2011 12:04 pm

Quoting Soxfan (Thread starter):
I've heard ground control telling aircraft taxiing behind large planes "caution wake turbulence." Can wake turbulence really push a plane around on the ground? Or, is it like a code for the second aircraft to maintain a certain distance behind the larger plane?

Basically, beware of the effects of the aircraft ahead.

It was a contributory factor in, though not the ultimate cause of, the crash of AA587 that hit the wake of a B747 that had taken off just before it.

http://en.wikipedia.org/wiki/American_Airlines_Flight_587
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bjorn14
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Wed Mar 09, 2011 12:30 am

About 30 years ago my stepfather was taking off /taxiing from ORD in a Beech 18 and got caught in the vortex of 747 which pushed him into a power station in which the airplane crashed and caught on fire. Fortunately he walked away from the crash with only a big bump on his head.
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Fly2HMO
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Wed Mar 09, 2011 3:22 am

This is something you should be more careful with on the ground http://www.youtube.com/watch?v=QXAvEQZC2kA


I was holding behind a 737 once in PHX in a wimpy C172, the exhaust wasn't even fully in our direction and even though we were about 300ft behind it, the moment he spooled up just a tad to start rolling again our plane was rocking like a boat in high seas. Nowhere to the point of getting blown over, but it felt like there was fat kids jumping on our wing tips trying to make it seesaw.
 
Bravo1Six
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Wed Mar 09, 2011 7:46 pm

Quoting Mir (Reply 1):
No, wake turbulence is not a factor on the ground - it's only created when an airplane is in the air. ATC only mentions it if the aircraft will be taking off behind the larger aircraft, meaning that the pilots will have to worry about it at that point.

-Mir

Wake turbulence commences at rotation of the aircraft generating the wake and only ends when the nose wheel is on the ground, so it's more correct to say that wake turbulence is created by, and is a function of, lift and not merely a creation of an aircrafy being in the air.

It is most certainly a factor on the ground for the aircraft that needs to pass through (whether via taxi, on the takeoff roll or on landing roll out) wake turbluence. As an example, an aircraft that taxis across the active runway just after arrival/departure of a heavy will need to be fully aware of any wake turbulence.
 
Viscount724
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Thu Mar 10, 2011 12:12 am

Quoting jetboy757 (Reply 4):
The definition of Wake Turbulence in the pilot/controller glossary...

WAKE TURBULENCE- Phenomena resulting from
the passage of an aircraft through the atmosphere.
The term includes vortices, thrust stream turbulence,
jet blast, jet wash, propeller wash, and rotor wash
both on the ground and in the air.

Following is the Transport Canada definition:

wake turbulence

Turbulent air behind an aircraft caused by any of the following:

(a) wing-tip vortices;

(b) rotor-tip vortices;

(c) jet-engine thrust stream or jet blast;

(d) rotor downwash;

(e) prop wash.
 
Soxfan
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Fri Mar 18, 2011 2:30 am

Thanks for all the great responses!

Quoting ThirtyEcho (Reply 3):

When a controller says "caution wake turbulence" it's a legal cover so in the event that something happens the FAA can say that they were warned. It is not a code with a set amount of distance, it's just a heads up to the pilot.

So should the controller say "caution wake turbulence" to every aircraft then, just to be safe, regardless of who or what is in front of them or around them? I'm trying to think of when it would be a good idea _not_ to say it to a pilot, especially if it doesn't require the pilot to do anything drastically different.
Pilot: "Request push, which way should we face?" JFK Ground: "You better face the front, sir, or you'll scare the pax!"
 
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Starlionblue
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Fri Mar 18, 2011 2:39 am

Quoting bravo1six (Reply 8):
Wake turbulence commences at rotation of the aircraft generating the wake and only ends when the nose wheel is on the ground, so it's more correct to say that wake turbulence is created by, and is a function of, lift and not merely a creation of an aircrafy being in the air.

I would think that it actually starts once the wings start producing lift, which is long before rotation.
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tdscanuck
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Fri Mar 18, 2011 4:16 am

Quoting Starlionblue (Reply 11):
I would think that it actually starts once the wings start producing lift, which is long before rotation.

True, but for typical rotation angles the lift coefficient jumps by about 1.6 so the change in wake generation is pretty substantial.

Tom.
 
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Starlionblue
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Fri Mar 18, 2011 5:54 am

Ah I see. A difference between "theoretical" and "significant in the real world". Thanks Tom.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
jetboy757
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Sat Mar 19, 2011 5:29 am

Quote:
So should the controller say "caution wake turbulence" to every aircraft then, just to be safe, regardless of who or what is in front of them or around them? I'm trying to think of when it would be a good idea _not_ to say it to a pilot, especially if it doesn't require the pilot to do anything drastically different.

It isn't necessary for a controller to say it to every aircraft. Just where the 7110.65 says it's required (usually only for departing or arriving aircraft), and where the controller feels it is necessary. For example if a helicopter is flying in close proximity to a Cessna 172, I would tell the Cessna caution wake turbulence. But if a helicopter was flying in close proximity to a Boeing 747 I wouldn't. If a Boeing 717 departed and another Boeing 717 departed I wouldn't.
 
AtcStudent
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Sat Apr 02, 2011 1:02 am

Quoting oly720man (Reply 5):
It was a contributory factor in, though not the ultimate cause of, the crash of AA587 that hit the wake of a B747 that had taken off just before it.

http://en.wikipedia.org/wiki/American_Airlines_Flight_587

I could be wrong, but the wake that the B747 left for AA587 (wingtip vorticies I think, I have a test on this on tuesday), travels down and in, and don't wingtip vortecies have no effect on the ground?
 
tdscanuck
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Sat Apr 02, 2011 3:00 am

Quoting ATCstudent (Reply 15):
I could be wrong, but the wake that the B747 left for AA587 (wingtip vorticies I think, I have a test on this on tuesday), travels down and in, and don't wingtip vortecies have no effect on the ground?

Wingtip vortices do have an effect on the ground if they reach the ground before they break up.

The initial path is down and inward (each vortex goes down due to the induced flow from the other one, and they move together because the downflow between them is lower pressure than the upflow outside).

If they hit the ground, they tend to spread out since the air between them now has nowhere to go. If you hang out near the approach end of runways, you can sometimes hear them.

Tom.
 
Malmi18
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Sat Apr 09, 2011 10:49 pm

Would be interesting to hear first hand experience from SXM, how the downwash / wake turbulence feels there when it hits the beach. The pics always capture the surreal moment before, when everythig is still calm.

On the other hand, I saw a couple of videos from there and the plane seemed to cause even surprisingly little sandstorm or similar.

So what is the reality? Does the camera get full of sand? Is it difficult to keep standing? Need to hold the skirt down? ehh..
 
 
HaveBlue
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Sun Apr 10, 2011 5:17 am

Quoting tdscanuck (Reply 16):
The initial path is down and inward (each vortex goes down due to the induced flow from the other one, and they move together because the downflow between them is lower pressure than the upflow outside).

I've always been taught its downward and outward, which explained how inflight refueling can be acheived behind and below such heavy aircraft as KC-135's and KC-10's.
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tdscanuck
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RE: Effect Of Wake Turbulence On Aircraft On Ground

Sun Apr 10, 2011 7:36 am

Quoting HaveBlue (Reply 18):

I've always been taught its downward and outward, which explained how inflight refueling can be acheived behind and below such heavy aircraft as KC-135's and KC-10's.

Definitely downward. Outward should only occur in proximity to the ground...at altitude, the vortices usually end up about a semi-span apart (i.e. they've moved together relative to the wingtips).

For refueling behind heavies, you're not far enough back for the vortex to have even fully formed (it takes about a semi-span to form) and significant downward/inward motion happens even more aft that that.

Tom.

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