N353SK
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Spacing Behind Heavys - On The Taxiway?

Tue Aug 07, 2007 11:33 am

After viewing this photo:



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Photo © Nitin Sarin




I began to wonder if there is a set protocol regarding small aircraft being behind large aircraft on the taxiway. Is there ever a risk of a large aircraft (say, a 777) producing so much thrust while taxiing that a smaller aircraft is in danger of being, for lack of a better term, "blown away?" I have an image in my head of a 777 applying thrust to move forward and a Cessna 152 blowing away like a leaf in the breeze. Does ATC tell small aircraft to beware or is it the pilot of the small craft's responsibility to tread lightly?
 
IAHFLYR
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RE: Spacing Behind Heavys - On The Taxiway?

Tue Aug 07, 2007 11:38 am

Quoting N353SK (Thread starter):
risk of a large aircraft (say, a 777) producing so much thrust while taxiing that a smaller aircraft is in danger of being, for lack of a better term, "blown away?"

Absolutely......I've been well behind an E45X on a taxiway when they have powered up to move and been shaken quite a bit in a C210. I always try to avoid having the fuselage at a 90 degree angle to any larger aircraft.

Quoting N353SK (Thread starter):
Does ATC tell small aircraft to beware or is it the pilot of the small craft's responsibility to tread lightly?

I've always told smaller aircraft to be aware.....a requirement, no, not unless they changed the book again and didn't tell everyone!
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Mir
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RE: Spacing Behind Heavys - On The Taxiway?

Tue Aug 07, 2007 12:05 pm

Quoting IAHFLYR (Reply 1):
a requirement, no, not unless they changed the book again and didn't tell everyone!

There's a little note in 7110.65 3-7-3 which says "use caution when taxiing smaller aircraft/helicopters in the vicinity of larger aircraft", as well as a sentence saying that clearances that require heavy jet aircraft to use greater than normal taxiing power should be avoided, and that small aircraft shouldn't be moved too close to taxiing or hover-taxiing helicopters.

That's about all I could find. I thought there was some sort of jet blast warning (or at least phraseology) in there, but couldn't find it.

-Mir
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dw747400
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RE: Spacing Behind Heavys - On The Taxiway?

Tue Aug 07, 2007 3:10 pm

Quoting N353SK (Thread starter):
Is there ever a risk of a large aircraft (say, a 777) producing so much thrust while taxiing that a smaller aircraft is in danger of being, for lack of a better term, "blown away?"

In an interesting story tangentally related to your question:
Upon completing my PPL checkride, we parked next to a very big, very old Sikorsky (an S-61 I think) that, at the time, was getting ready to taxi out. Not knowing this, the examiner told me to park right next to him. In short, we had two people sit in the 172, with another two people holding the wing struts, but we still rocked and rolled when that chopper started to taxi.

Obviously, thats very different than a big jet, but in terms of moving large volumes of air very fast, a chopper rotor or a GE90 can both make for an interesting day.
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Spruit
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RE: Spacing Behind Heavys - On The Taxiway?

Tue Aug 07, 2007 7:09 pm

Quoting N353SK (Thread starter):
I began to wonder if there is a set protocol regarding small aircraft being behind large aircraft on the taxiway. Is there ever a risk of a large aircraft (say, a 777) producing so much thrust while taxiing that a smaller aircraft is in danger of being, for lack of a better term, "blown away?"

I think in relation to that picture you've posted the spacing is okay, but I for one, certainly wouldn't like to be taxying anything GA sized behind that T7 considering at idle thrust the GE90-115B exhaust velocities are about 30-50MPH!

Spru!
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HAWK21M
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RE: Spacing Behind Heavys - On The Taxiway?

Tue Aug 07, 2007 7:44 pm

Thats the Airport I work at.
Its the Angle of the photo thats giving the impression that they are very close up.The Pic is taken from a hill around 75 meters away & on a height of 100-150 feet.Also Taxiing out the B773ER would not be ramming up the thrust levers fwd as what one would think.
Adequate spacing is always maintained.
regds
MEL
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IAHFLYR
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RE: Spacing Behind Heavys - On The Taxiway?

Tue Aug 07, 2007 10:42 pm

Quoting Mir (Reply 2):
There's a little note in 7110.65 3-7-3 which says "use caution when taxiing smaller aircraft/helicopters in the vicinity of larger aircraft", as well as a sentence saying that clearances that require heavy jet aircraft to use greater than normal taxiing power should be avoided, and that small aircraft shouldn't be moved too close to taxiing or hover-taxiing helicopters.

Yes, but it is not a requirement to advise, simply a requirement to avoid issuing those type of clearances, but still a nice heads up to the small plane driver.
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atct
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RE: Spacing Behind Heavys - On The Taxiway?

Wed Aug 08, 2007 12:13 am

Yea there is no requirement telling me I cannot taxi a Cessna 172 (or even an ATR / Saab 340) behind a B772.

Now say when I launch a 777 and my next aircraft ready to go at the hold short is an ERJ or Saab etc., I'll usually say "Colgan 5435, Houston tower, runway 15L, 'your discretion' position and hold for wake turbulence" Some people like it, some people dont, but the way I look at it, if he rams the throttles and shoots out a second after the 777 has started to roll and something happens, Im clear.

Anywho as Mir stated, the only "requirement" I have is not to put a small or small + in position behind a departing heavy aircraft. (Less than 44,000lbs would be a small / +)

"3-7-3. GROUND OPERATIONS

WAKE TURBULENCE APPLICATION

Avoid clearances which require:

a. Heavy jet aircraft to use greater than normal taxiing power.

b. Small aircraft or helicopters to taxi in close proximity to taxiing or hover-taxi helicopters."

----

As one who has read alot of the 7110.65 in the past few years, this seems to be very vague. "Avoid Clearances" leaves open that you can still do it. I believe "Clearance shall not be given which require:" would be better if you could NOT do these at all. So what im thinking is you can do it, but just use caution.

Anywho thats my 2 Cents.

ATCT

(Note: This is all speculation and personel interpretation, not an official answer or guide, I will look into this matter more deeply at work)
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mark5388916
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RE: Spacing Behind Heavys - On The Taxiway?

Thu Aug 09, 2007 11:58 pm

Not quite the same but you can see what happens to a F-16 when it taxis too close to a B-1.



Mark

EDIT: I took this video off this thread B-1 Gets An F-16 Kill (by BladeLWS Jun 25 2007 in Military Aviation & Space Flight)

[Edited 2007-08-09 17:22:46]
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chksix
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RE: Spacing Behind Heavys - On The Taxiway?

Fri Aug 10, 2007 12:13 am

Interesting that the photographer missed it completely and filmed the takeoff instead!
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SlamClick
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RE: Spacing Behind Heavys - On The Taxiway?

Fri Aug 10, 2007 12:50 am

Quoting Chksix (Reply 9):
Interesting that the photographer missed it completely and filmed the takeoff instead!

"The board finds that the videographer lost situational awareness and, as a result, did not see the F-16 until it was too late."

* * *


Pilots of large jet airplanes are aware that they continue to be responsible for damage done by their jet blast. Almost everywhere in the world, all it takes to get rolling is just to release the brakes. There are a few exceptions of course. If the taxiway runs uphill it make take some handles-forward to get rolling. San Jose California, holding short of 32L used to be on asphalt and planes would sink in on a warm day. Other planes would "fall in" to the holes and require a lot of thrust to crawl up out of them. It was a very good idea not to place yourself right behind them.

As I once asked a Cessna pilot: If my engines will make my 180000 pound airplane fly five hundred miles per hour how fast will they make your two thousand pound airplane fly?
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smcmac32msn
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RE: Spacing Behind Heavys - On The Taxiway?

Fri Aug 10, 2007 1:04 am

Quoting SlamClick (Reply 10):
"The board finds that the videographer lost situational awareness and, as a result, did not see the F-16 until it was too late."

I didn't know we all came to that concensus, but I'm fine with that.
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Ceph
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RE: Spacing Behind Heavys - On The Taxiway?

Wed Aug 15, 2007 1:09 am

oops... how did they right the F-16? Did the plane get damaged?

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