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Author Topic: Wake Turbulence  (Read 7788 times)
JETSET843D
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« on: April 05, 2007, 10:19:47 PM »

Hello there,

I am currently listening to JFK ground and have a question re wake turbulence. As a pilot it is my understanding that wake turbulence is a bi product of lift and wake turbulences commences to be shed from an aircraft from the moment it becomes airborne to the moment it touches down.

My question is why do JFK ground tell aircraft taxying to the runway 'caution wake turbulence'Huh I would understand them informing the crew of this on the tower frequency but don't understand the relevence on informing the crew whilst taxying??

Can anyone shed any light on this, maybe even some JFK controllers??

Regards,

James
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Studentpilo
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« Reply #1 on: April 05, 2007, 11:07:44 PM »

Caution wake turbulence shouldnt be used on the ground. On the ground the exhaust and blast from the engines can cause damage, though (especially a 747's blast on a 172  grin). 7110.65 calls this "Jet Blast" and thus the proper phraseology is "Caution Jet Blast." Turboprops and helicopters can also create a good amount of wind with their engines on the ground and this is called "Prop Wash."

The only time I can imagine hearing "Caution wake turbulence" on the ground is if the plane is taxiing into position and hold.
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JETSET843D
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« Reply #2 on: April 05, 2007, 11:16:23 PM »

Yeah i initial thought the controllers were warning the pilot about the jet blast - but the term caution wake turbulence isn't appropriate.

I again agree that the only time one would expect a wake turbulence remark is from tower if you're taking off behind a heavy aircraft.

Have a listen to JFK ground they seem to use the phrase quite regularly??

Regards

James
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Miyridian
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« Reply #3 on: April 06, 2007, 12:29:54 AM »

I'd imagine that the ground controllers do it once the takeoff sequence has been established so that the tower controllers don't have to.
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JETSET843D
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« Reply #4 on: April 06, 2007, 12:38:22 AM »

Thanks Miyridian for the clarification grin

That would make sense.

Regards

James
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rpd
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« Reply #5 on: April 06, 2007, 12:58:00 AM »

Wake turbulance vortices certainly can affect aircraft on the ground.  The vortices naturally drift away from the aircraft in a sinking motion, and can linger for up to 1000 feet vertically.  Any wind can affect the drift of the vortice as far as where it drifts and how fast.  Aircraft on taxiways near the approach end or departure end of the runway or crossing a runway after a departure could be affected.

This should also be moved out of the clips forum smiley
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JETSET843D
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« Reply #6 on: April 06, 2007, 01:04:43 AM »

Hi,

I remember from my ATPL ground school that vortices can descent upto 1000 feet and in still wind they disperse outward and wind would obviously 'blow' the vortices in relevent direction.

Forgive my ignorance but i really don't see how wake vortices can affect an aircraft taxying on an airfield??

Can anyone please elaborate??

Regards

James
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davolijj
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« Reply #7 on: April 06, 2007, 01:09:05 AM »

The term Wake Turbulence is perfectly appropriate during cautionary advisories to aircraft engaged in taxi and ground movement operations. Other terms like jet blast, propwash, etc., may be more specific but the 7110.65 states that these terms aren't mandatory.  Here is a note at the bottom of the general control section on the issue:

Quote from: 7110.65R Chapter 2, Section 1
2-1-20. WAKE TURBULENCE CAUTIONARY ADVISORIES

NOTE-
Wake turbulence may be encountered by aircraft in flight as well as when operating on the airport movement area. Because wake turbulence is unpredictable, the controller is not responsible for anticipating its existence or effect. Although not mandatory during ground operations, controllers may use the words jet blast, propwash, or rotorwash, in lieu of wake turbulence, when issuing a caution advisory.
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Regards
JD
JETSET843D
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« Reply #8 on: April 06, 2007, 01:23:18 AM »

Many thanks JD.

I've learnt something new this evening, i never realised aircraft were at risk of encountering wake turbulence in the manoeuvring area.

Thanks for all your input chaps,

Regards

James
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Pearson
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« Reply #9 on: April 06, 2007, 01:40:44 AM »

Yeah, it's pretty much a better safe than sorry thing.  Especially at Kennedy...AA587 might have a little something to do with it, too.
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LHP50
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« Reply #10 on: April 08, 2007, 11:29:41 PM »

JD is right.  From 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.

In the 1980s at LAXT I remember having to change my ground control phraseology from 'jet blast' to 'wake turbulence'.  I also remember seeing a Cessna relocated a few hundred feet when taxiing accross a rwy that a DC10 just started takeoff roll on.

LH

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