Wx Watch: Running the Numbers

Statistics can be boring, but sometimes they speak eloquently. Such is the case with the National Transportation Safety Board's rundown of weather-related accidents. According to data from the AOPA Air Safety Foundation's accident database, the NTSB reported a total of 11,053 general aviation accidents in the period from 1988 to 1992. Of that total, 21 percent, or 2,347 accidents, were deemed "weather-related." That means that weather was named as a cause or factor in those accidents — not necessarily the cause or the primary factor, but a big player in the events leading up to this kind of crash.

Now let's look at the kinds of weather phenomena that cause problems. Go ahead, take a guess at the hands-down, all-time winner as pilotdom's biggest weather ogre. Thunderstorms, you say? Well, they're definitely on the list of troublemakers and help to cause about 10 to 15 fatal accidents a year. But in the grand scheme of things, they certainly don't lead the pack when it comes to their place in the "total accidents" column.

No, the single biggest cause or factor in a weather-related accident is listed as adverse winds. Some 42 percent of those 2,347 weather-related accidents were blamed, in part, on gusty, shifting, or strong winds. This category also takes in such bad setups as tailwinds during the landing phase of flight. Indeed, most of the adverse-wind category involves loss of directional control just before, during, and after landing.

While adverse winds account for very few injuries, they are responsible for a great deal of airframe, propeller, and powerplant damage. Fact is, adverse-wind accidents produce a tremendous number of insurance claims. So while adverse winds may not hurt or kill you, as accident-producers they deserve more respect than they get. Statistically, you are much more at risk of having an accident while fighting an ugly crosswind than you are flying in instrument meteorological conditions.

Which brings us to the number-two weather problem: low ceilings and visibilities. These were named in 24 percent of the total weather accidents. But unlike adverse winds, low ceilings and poor visibility do have records as killers.

Here's how the rest of the list plays out. Turbulence is cited in eight percent of weather accidents, density altitude in another eight percent, icing in yet another eight percent, precipitation appears in seven percent of reports (I'm assuming that visibility restrictions accompany this category), thunderstorms claim just two percent, and wind shear a mere one percent.

Now let's break this total pool of weather-related accidents down by mission. Most of them — 70 percent — occurred on personal flights. Ten percent involved the business flying category, 13 percent were on instructional flights, and one percent happened on executive or corporate flight operations. Summed up, this means that owner-flown aircraft on pleasure flights seem to be at an unusually high risk of having wind-related directional control problems on landing and are less likely to have problems flying in poor visibilities or low ceilings.

Because of his training and experience level, the typical pilot flying his airplane on business faces less likelihood of a problem dealing with adverse winds. Low ceilings and visibilities are listed in 35 percent of business flying's 10-percent share of the weather- related accident pie, or 78 crashes. A close second place goes to adverse winds, with 26 percent of accidents, or about 58 mishaps. Then comes the precipitation category, with 12 percent; icing, with 10 percent; turbulence, with nine percent; thunderstorms, with four percent (that's just nine accidents in four years); and density altitude, with three percent.

How do professionally flown executive and corporate flights fare? This group listed 53 percent of their weather accidents as being affected by low ceilings and visibilities. Twenty percent named precipitation, 15 percent blamed adverse winds, and 12 percent were caused by combinations of the other weather events already listed in the previous groups.

The unscientific conclusion? First, we all have to spend more time honing our crosswind landing skills and our attention to airspeed and directional control during the landing phase. Second, those of us who don't have instrument ratings, or who are lapsed instrument pilots, simply have to learn to give IFR weather a wide berth and know when to execute that all-important 180-degree turn to exit deteriorating weather. Third, those of us who regularly fly on instrument flight plans have to practice often enough to ensure that proper procedures are unswervingly followed.

You've probably noticed by now that I haven't been spouting off details about fatal weather-related accidents. (Okay, here's a tidbit: 35 percent of all fatal general aviation accidents are weather related.)

There's a reason for not dwelling on the fatal phenomena here. I think that many pilots (truth be known, probably three-fourths or more) limit their flying to good VFR weather. They're probably a little rustier than they'd like to admit, too. So while this group of pilots exercises good judgment by not flying when low clouds, lousy visibility, thunderstorms, or icing are around, they may not be aware of the statistical risk they face by flying in "good" weather. A few trips around the pattern to regain currency is a great idea, but having an instructor aboard is an even better one. As we've seen, quirky winds do the most damage — if not to the pilots, then to their airplanes. And an accident is an accident, no matter how you look at it.

And now, a final statistic. One that requires no comment. Records show that 55 percent of the pilots involved in weather- related accidents never received a weather briefing.