Q: What do pilots need to understand about flying in moderate to heavy rain?
How could you even ask that? Do you know what rain in an open cockpit does to fine leather?
Jokes aside, flying in the rain really isn't that big of a deal...except when it's an extremely big deal. For example, flying your single-engine piston in moderate rain won’t even get the attention of your airplane, let alone cause it any undue consternation. The lift from your wings is virtually unaffected, and the engine will continue to run just fine (as long as the rain isn’t so heavy as to prevent sufficient air from being supplied to it).
Of course, this is all assuming the rain hasn’t reduced your visibility below legal limits (if you’re flying VFR) or, more importantly, below your personal limits. This also assumes none of the rain turns to ice on your wings, in your pitot tube, or in the venturi of a carbureted engine (which it totally could).
Your preparation for precipitation should always begin in the same place: on the ground before your flight. And, of course, your very first preflight planning activity should be to review this article and my video on known icing conditions.
Then you can get to all the other things you should do, like studying the progs well before your flight and getting a thorough weather briefing just before you take to the skies.
Also, and this is very important, think about what the weather might do if the forecast is not perfectly accurate. How will you react? What’s your Plan B? What will you do if the rain looks too heavy for your comfort level, you think icing might occur, or — heaven forbid — does start to occur? Will you divert to the nearest airport behind you? Descend to get out of freezing temperatures? Turn back?
Whatever it is, decide what you’ll do before you set one toe in your airplane! And commit to yourself that you will execute your backup plans should the need arise. Continuing to fly ahead while you wait to see if the weather improves is a recipe for disaster, a dead-end road, a losing battle, a lost cause, an ill wind that blows good to nobody, a tinderbox with gasoline and a match, a veritable minefield!
In other words, it's not a good idea.
How to land
Finally, let’s talk about the final phase of flying in the rain, which is landing in the rain. Hydroplaning can bring an otherwise fabulous flight to a fraught finish. But how do you know if you’ll hydroplane when you land (or when you take off, for that matter)? Just remember this one thing.
Nine times the square root of tire pressure.
Remember it for me...remember it for Captain Harv. The speed at which your landing gears will hydroplane, in knots, can be determined by multiplying the square root of your tire pressure by nine. So, if you have 30 pounds per square inch, or 30 psi of tire pressure, we get a square root of about 5.5. If you multiply that by nine, you get about 50 knots.
So, when landing in your Skyhawk, you may want to consider putting rubber to asphalt somewhere in the 40-something knot range. And if you’re taking off, your rotate speed is 55 knots. So, maybe let the sun dry things out a little before departure.
Until next time...you’re welcome.
Capt. Harv is the greatest pilot to ever live...if you ask him. When he isn't flying circles around you without ever leaving straight-and-level flight, he's straightening out your questions about aviation on the worldwide web. Follow him on Twitter and YouTube to become a better pilot.