Another Pilot Question
I just finished a trip to Bangkok. Flew from Atlanta to Narita on the way out. It was a tad bumpy but not bad – though they kept the seat belt sign on almost the whole way. Somewhere out there in the middle of nowhere we did hit some sudden and rather jarring bumps. Almost like hitting a set of speed bumps too fast in the car.
Someone from the cockpit came on the intercom and said we had hit turbulence from another aircraft that had crossed our path.
How close would we have had to come for that to happen like that?
I was on a 777 – not sure about altitude.
Thanks to anyone who might know.
Posted by JR
On September 28th, 2010 under Unfiled.
Comments: 1
Comments
Comment from MaxDamage
Time: October 14, 2010, 11:41 pm
Short answer, you could have felt this several miles away.
Long answer: a 777 is a big machine, with a lot of wing area, and it’s moving at a pretty good pace. Those sudden climbs and dips you feel after taking off and shortly before landing are just the change of ambient air density, and hence pressure, due to slight differences in air temperature near the surface. An asphalt parking lot heats the air and makes it go up a bit, a river cools the air and makes it go down a bit. That’s why the ride is so bumpy at low altitude — air is moving around.
Well, a 767 or 747 ahead of you produces a much larger disturbance in stable air than a small parking lot being hot does, and it produces that disturbance at your altitude instead of having dampened out by 15000 feet or so. Also, it’s disturbing the air a lot more than the parking lot is.
So, in a nut-shell, depending upon air speed variations you could have passed 5 miles away and it would feel as if you were in a Cessna at 1500′ getting buffeted by the thermals off a large city. Which it apparently did.
– Max
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