Thank you,
Ben
Greetings Ben,
Though the reasoning behind the FAA's rules isn't always clear, I think the explanation is that high-performance airplanes typically climb a lot faster than they descend. For instance, a high-performance business jet may climb at several thousands of feet per minute immediately after departure. The same jet typically descends at less than 1,000 feet per minute when it's within a few thousand feet of the ground. It follows that you will need more altitude above a cloud than below it to permit the same reaction time within which to see, be seen by, and avoid a rapidly climbing high-performance aircraft.
You'll also notice that at altitudes above 10,000 feet msl, the cloud clearance distances above and below a cloud are the same: 1,000 feet above and 1,000 feet below. High-performance aircraft are more likely to make faster descents at altitudes above 10,000 feet msl. The regulations thus require that you be at a greater distance below the clouds at these altitudes.
VFR Weather Judgment
Dear Rod,
I earned my private pilot certificate a few weeks ago, and my question is this: What steps should a VFR pilot take to determine if the weather is good enough for a VFR flight?
I was taught in ground school about minimum visibility and ceiling, but when it comes to actual safe weather prediction, I still need to know what the margin of safety should be and how thorough I should be.
I reserve planes from the local club. I call the FSS for an outlook the day before, then for a briefing on the flight day. The standard briefing is very extensive and sometimes overwhelming; sometimes the briefer states that visibility is low and it's a marginal VFR condition, but it looks very clear and sunny at the airport.
When my flight instructor sees me canceling a reservation, he encourages me to fly and says, "Come on, Harry, it's nice." I also see many people I know flying that day.
Thank you,
Harry
Greetings Harry,
Many years ago I learned a very important thing about weather: If you always wait for the forecast of perfect weather before you fly, then you won't fly much.
Meteorology isn't an exact science, which is why weather forecasters use probabilities when discussing weather. Thus, when my buddy at the FSS asks for my name, I tell him that there's a 50 percent chance that it will be Rod Machado, depending on how the briefing goes. And yes, when the FSS specialist says, "VFR not recommended," it sometimes turns out to be a beautiful day. That's because we live in Reality Land, not Disneyland.
Here's what I recommend. First, if you haven't already done so, it's imperative that you define and establish personal weather minimums. You need some objective criteria with which to begin the decision process. If you don't know how to begin defining these minima, then ask those whose judgment you trust to help you select the individual weather criterion you'll use to make these decisions (e.g., minimum ceiling, visibility, wind velocity, etc.).
To determine if the weather is good enough for a VFR flight, obtain the appropriate weather briefing and pay particular attention to the METAR, TAF, area forecast, and weather depiction chart. Let's suppose that these and other reports indicate that your personal minimums exist or are expected to exist for the entire route. Let's also suppose that the reports suggest that the weather will remain within acceptable limits for the return flight, too. Given these conditions, get in the airplane and fly. At this point, the only way to tell what's really happening weather-wise is to have a look.
Let's suppose that the weather looks iffy. It's entirely possible that the FSS specialist will suggest that VFR isn't recommended, but when you look out the window, it's beautiful. You have two choices: Stay put or take a look-see.
As a private pilot, I don't think it's at all unreasonable to depart on a trip under such conditions as long as you follow one caveat: You must always - always! - have a way out in case the weather turns sour. There are no exceptions to this rule.
This might mean that you plan your route near enough to another airport in case you need to land. It might also mean flying a zig-zag course from one nearby airport to the next until reaching your destination. Once you gain more experience, you won't need to do this, but you'll always want to know where the nearest airport is - always!
If the weather turns nasty, then make your retreat along the same route back to the departure airport or land at one of the intermediate airports if necessary. In other words, the less confident you are about the weather or your ability to predict and understand it, the closer you should be to an airport along your route in case you need to put the airplane down.
The things that can cause problems with this strategy are strong winds or strong crosswinds. While you can see and avoid clouds during the day as well as estimate visibility, you can't see wind. It's possible to depart in calm wind only to find that the crosswind landing conditions at the destination airport are beyond your skill level. Now, if all the airports along your route had two or more criss-crossing runways, you wouldn't worry as much about crosswinds. Unfortunately, not all airports are like this. Therefore, if the METAR indicates strong airport winds (or the TAF predicts them), then your decision to depart must be evaluated based on your skill at handling the anticipated winds. One of the very best gifts you can give yourself to aid in cross-country confidence is to improve your skill at crosswind landings.
Sometimes, however, we just want some sort of personal assurance about the weather at the destination before departure. Yes, you can get this from the METAR or you can even phone the airport to obtain its recorded ATIS or live AWOS information. Often, however, it's just more reassuring to talk to a human being at the destination to ask about the current conditions. If this is what it takes to make you feel better, then call someone at your destination.
This is a good reason to have AOPA's Airport Directory, which includes telephone numbers for airport businesses. (The directory is available on AOPA Online [http://data.aopa2.org/airport/ index.cfm]). Over the years I've called many airports to ask about weather or local procedures. Call an FBO and ask to speak to a flight instructor. Ask him or her to tell you about current conditions or the peculiarities of local weather phenomena. This is just one more bit of information to help with your decision.
Harry, to gain confidence regarding weather, you must fly and experience weather. If you have to land at an intermediate airport because conditions go below your minimums, then do so. In time you'll get better at understanding the weather. If you only fly in perfect weather, it's unlikely that you'll ever feel much confidence.
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