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Effect Of Wake Turbulence On Aircraft On Ground  
User currently offlineSoxfan From United States of America, joined Mar 2008, 864 posts, RR: 0
Posted (3 years 5 months 2 weeks 2 days 22 hours ago) and read 6982 times:

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!"
19 replies: All unread, jump to last
 
User currently offlineMir From United States of America, joined Jan 2004, 21552 posts, RR: 55
Reply 1, posted (3 years 5 months 2 weeks 2 days 22 hours ago) and read 6981 times:

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



7 billion, one nation, imagination...it's a beautiful day
User currently offline26point2 From United States of America, joined Mar 2010, 817 posts, RR: 0
Reply 2, posted (3 years 5 months 2 weeks 2 days 21 hours ago) and read 6971 times:

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.

User currently offlineThirtyEcho From United States of America, joined Dec 2001, 1645 posts, RR: 1
Reply 3, posted (3 years 5 months 2 weeks 2 days 20 hours ago) and read 6949 times:

Airborne helicopters can pose a hazard to taxiing light aircraft on the ground.

User currently offlinejetboy757 From United States of America, joined May 2006, 53 posts, RR: 0
Reply 4, posted (3 years 5 months 2 weeks 2 days 16 hours ago) and read 6879 times:

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]

User currently offlineoly720man From United Kingdom, joined May 2004, 6696 posts, RR: 11
Reply 5, posted (3 years 5 months 2 weeks 2 days 13 hours ago) and read 6823 times:

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



wheat and dairy can screw up your brain
User currently offlinebjorn14 From Norway, joined Feb 2010, 3411 posts, RR: 2
Reply 6, posted (3 years 5 months 2 weeks 2 days ago) and read 6662 times:

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.


"I want to know the voice of God the rest is just details" --A. Einstein
User currently offlineFly2HMO From , joined Dec 1969, posts, RR:
Reply 7, posted (3 years 5 months 2 weeks 1 day 22 hours ago) and read 6622 times:

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.


User currently offlinebravo1six From Canada, joined Dec 2007, 397 posts, RR: 2
Reply 8, posted (3 years 5 months 2 weeks 1 day 5 hours ago) and read 6488 times:

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.


User currently onlineViscount724 From Switzerland, joined Oct 2006, 25108 posts, RR: 22
Reply 9, posted (3 years 5 months 2 weeks 1 day 1 hour ago) and read 6437 times:

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.


User currently offlineSoxfan From United States of America, joined Mar 2008, 864 posts, RR: 0
Reply 10, posted (3 years 5 months 6 days 22 hours ago) and read 6095 times:

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!"
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17015 posts, RR: 67
Reply 11, posted (3 years 5 months 6 days 22 hours ago) and read 6092 times:

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.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 12, posted (3 years 5 months 6 days 21 hours ago) and read 6083 times:

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.


User currently offlineStarlionblue From Greenland, joined Feb 2004, 17015 posts, RR: 67
Reply 13, posted (3 years 5 months 6 days 19 hours ago) and read 6077 times:

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."
User currently offlinejetboy757 From United States of America, joined May 2006, 53 posts, RR: 0
Reply 14, posted (3 years 5 months 5 days 19 hours ago) and read 5952 times:

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.


User currently offlineATCstudent From United States of America, joined Mar 2011, 12 posts, RR: 0
Reply 15, posted (3 years 4 months 3 weeks 1 day ago) and read 5571 times:

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?


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 16, posted (3 years 4 months 3 weeks 22 hours ago) and read 5558 times:

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.


User currently offlineMalmi18 From Finland, joined Oct 2007, 13 posts, RR: 0
Reply 17, posted (3 years 4 months 2 weeks 2 hours ago) and read 5252 times:

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..
 


User currently offlineHaveBlue From United States of America, joined Jan 2004, 2103 posts, RR: 1
Reply 18, posted (3 years 4 months 1 week 6 days 20 hours ago) and read 5185 times:

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.



Here Here for Severe Clear!
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 19, posted (3 years 4 months 1 week 6 days 17 hours ago) and read 5166 times:

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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