Flying over the runway

[ryan_d_sucks 0]

As a student I'm often told not to fly over the runway.. Or at least I was when I first started. My question is why? Is it purely an issue of risking a collision with oncoming aircraft traffic? Or is there something about the way heat rises from the blacktop that will affect canopy flight?

The reason I ask is because at my DZ the landing area is very close to the runway, and if the winds are out of the east or west you will usually end up close to, or wanting to cross the runway either on your downwind or base leg of your approach.

Last season we had a canopy collapse at probably 20-30 feet (I'm guessing, I wasn't there) as the jumper flew over the runway on a very hot day (resulting in knee surgery). Does that collapse have anything to do with being over the runway, or might that just be coincidence? From my understanding she wasn't near the hangers or any other turbulence causing obstacles. So is it just an issue of other air traffic, or is there something about blacktop and heat that affects canopy flight?

[phoenixlpr 0]

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Is it purely an issue of risking a collision with oncoming aircraft traffic?

Bingo. An active runway usually has a no fly zone for canopies under 300m.

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Or is there something about the way heat rises from the blacktop that will affect canopy flight?

You might find a column of air rising over the dark runway headed by the sun, so may expect some turbulence there.

[BIGUN 1,073]

Just one example...

Gus Wing

Nobody has time to listen; because they're desperately chasing the need of being heard.

[kschilk 0]

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Is it purely an issue of risking a collision with oncoming aircraft traffic?

Bingo. An active runway usually has a no fly zone for canopies under 300m.

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Or is there something about the way heat rises from the blacktop that will affect canopy flight?

You might find a column of air rising over the dark runway headed by the sun, so may expect some turbulence there.

It's a breeding ground for those pesky li'l dust-devils, too.

"T'was ever thus."

[tombuch 0]

Airplanes are the obvious concern, but you hit the nail on the head when you asked about wind.

The runway will usually heat up much faster than the surrounding dirt or grass, and that will create a column of rising air. Where air rises, cooler air from the surrounding ground will sink and fill the void. That creates rapidly rising air over the runway, and equally strong downdrafts over the surrounding grass/dirt, with sideways movement near the surface. There may also often be a defined shear between the two moving air masses, and a sheer or transition zone between the grass along the runway and the rest of the landing zone. Those downdrafts can be nasty, and may have been the cause of the collapse you wrote about.

On a hot and still day the patterns of rising and falling air will be in obvious locations, but if there is a cross wind those air masses will be offset, so you need to think about any wind, no matter how slight.

As somebody else noted, there may also be dust devils formed by the conflicting air masses, and those can spin quite a distance away from the source, especially if there is a very slight breeze.

In any case, the lifting air can move quite high. I've held in breaks for a good 20 minutes alongside a concrete runway, 1,000 feet above the surface, with a pretty heavily loaded canopy. I've also used that rising air column to get back from a long spot, then moved aggressively to the side, high enough to avoid the strongest downdraft.

Micro-meteorology is pretty fun stuff. If you understand how the surface of the planet heats, and how air current moves, you can fly your parachute like a glider and gain tremendous performance, while also avoiding potential trouble spots, and having a blast of a good time doing it. I'm also an FAA certificated glider pilot, so I sometimes really groove on those hot and sunny days. If this is stuff that interests you, there are some good meteorology books written for glider and hang glider pilots. And heck, your skydiving experience may even take you into those other forms of recreational aviation.

Tom Buchanan
Instructor Emeritus
Comm Pilot MSEL,G
Author: JUMP! Skydiving Made Fun and Easy

[Colson 0]

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there are some good meteorology books written for glider and hang glider pilots.

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Got any names or isbn #'s? I kept most of my college meterology stuff, and all the flight training materials, but Im always looking for the next good read.

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[PhreeZone 15]

Understanding the Sky by Dennis Pagen is said to be the holy grail of micrometeorology for all sport aviators. Look for its reviews on paragliding forums.

Yesterday is history
And tomorrow is a mystery

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