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Above or below?

The waterline doesn’t lie

You’re cruising along VFR in clear skies, but clouds are visible miles ahead.

Water Bottle

It’s hard to judge whether you’ll top the clouds at your current altitude, but it would be good to decide well in advance whether to go over, under, or around them. The sooner you start climbing, descending, or turning, the smoother and less dramatic the changes will be for your passengers.

Is there anything in the cockpit that can help you make an informed choice?

Yes. The bottle of water you took from the FBO is all you need.

Drink about half, peel off the label, then put the cap back on and turn the bottle on its side. Hold it level directly in front of your eyes, and gaze ahead at the clouds.

If the tops of the clouds are visible above the waterline, they’re above you. If the cloud tops are below the waterline, you’ll overfly them. The waterline doesn’t lie.

Of course, there are limits to the usefulness of this trick. Clouds are dynamic, and they may rise during the time it takes to reach them. Also, even light chop can make it nearly impossible to get an accurate waterline reading. It helps to be in still air.

But the next time you’re faced with an over/under/around cloud choice, don’t bury your head in an iPad looking for cloud-top reports that likely are dated, if they exist at all. Better to grab a water bottle and see for yourself.

You’ll be surprised how well it works.

Dave Hirschman

Dave Hirschman

AOPA Pilot Editor at Large
AOPA Pilot Editor at Large Dave Hirschman joined AOPA in 2008. He has an airline transport pilot certificate and instrument and multiengine flight instructor certificates. Dave flies vintage, historical, and Experimental airplanes and specializes in tailwheel and aerobatic instruction.

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