Safety Pilot: Weather windows

March 1, 2009

Bruce Landsberg has logged more than 6,000 flight hours and holds multiple ratings.

What a difference a day makes! It’s axiomatic in the accident investigation business that the wreckage is usually picked up in good weather. As the AOPA Air Safety Foundation analyzes dozens of weather-related accidents each year, I’m struck by the fact that so many could have been avoided—not by not going, but rather by being a little smarter about when they went.

Weather is a four-dimensional adversary, and since adverse weather often covers such a large area, timing is the most easily addressed variable. Weather windows have been around for centuries and have been used by sailors whose craft, very much like our own, are highly weather vulnerable. For example, with a frontal passage and concurrent high winds, most sailors will wait a day or so before launching on an extended navigation. If the trip is not longer than a few days, they will likely be in the lull between systems.

Sailing magazines and books abound with sea stories (sorry) of both comfortable and terrible passages based on how well sailors and forecasters judged the weather window. Most of the time it works, and only fools put out to sea when adverse weather is forecast. They usually live to tell about it and don’t make the same mistake twice. The boats are very strong and forgiving, but the ride is anything but pleasant. In GA, the physics are quite different, and we’re not always that lucky.

Being able to go earlier or later is the key. The airlines practice late departures or cancellations all the time, and they’d go early if they could get away with it. Despite the aggravation this can cause, their safety record is impeccable. This past holiday season is testimony to the need for flexibility. The airlines have superb equipment and crews trained to handle a much broader range of weather. If they use the weather window concept, shouldn’t we? They are working with the operational window, as opposed to the planning window, which we’ll get to momentarily. The reality of travel these days, both airline and GA, is flexibility. To say we always go where and when we want is a Pinocchio statement. There is some truth, but let’s just say we’ve all been guilty of some “shading.”

A few examples from my logbook illustrate weather windows. When my youngest son was going to college several states away, the three-hour flight compared to the nine-hour drive was always preferable. In the winter, not having a deiced aircraft available, we planned a weather window of several days. The southern end of the trip was usually OK, but the northern end could be problematic. So a typical three-day weekend trip that would normally begin Friday morning sometimes meant a late Thursday departure with returns earlier Sunday or late Monday.

During convective season it’s usually a little easier in that we can pretty well bet that afternoons will be nasty—but not always. Last spring on a trip from Florida, I had a late-morning return to the Washington, D.C., area. There was an unsettled area that just seemed to hang around Washington (that’s a meteorological, not a political comment). I watched the blobs of lightning and heavy precip grow, dissipate, and grow again on the weather datalink all morning as I flew north. About 100 miles south of the destination, delay seemed like the smart thing to do. Two hours later the storms finally moved on, and I had a nice ride in—weather-window flying at its best. That was an operational window.

Unlike sailing, operational GA weather windows typically are measured in half days rather than several days since most GA flights don’t last longer than about four to five hours. That’s a huge benefit because short-range forecasting is becoming quite accurate. The actual flight decision can usually be made with reasonably good information, with some notable exceptions that I’ve commented on before.

The planning window should include the day before to the day after the optimum flight day. For example, suppose there’s a family outing set for the weekend. The plan is to leave Friday afternoon, but the forecast is for low ceilings and possibly thunderstorms. The obvious answer is to go Friday morning, but suppose the front is already active or moving faster? Maybe a late Thursday launch will work, or early Saturday morning. Time is the crucial variable because whatever crummy thing the weather is doing, it will ultimately be doing it somewhere else later. How much sooner or later is the question.

The planning weather window has to be quite a bit wider if you’re not instrument rated (and proficient) and the aircraft properly equipped. Most of the time, a three-day window will work very well, but occasionally a weather system will bog down and a VFR pilot will be stuck (depending on the situation, IFR pilots can get stuck as well). Flying to eastern Canada, I once encountered some widespread unforecast instrument conditions caused by heavy smoke carried on the prevailing winds from forest fires 150 miles away. Since it was mid-summer there were no nearby fronts to clear the air. After my ILS approach a VFR pilot came up to ask the conditions, knowing full well what the answer was. He’d been stranded there since the preceding afternoon and, as far as I know, ultimately rented a car to get out. The smoke hung around another two days.

Try this. Go to AOPA’s new Internet Flight Planner and pick a day a week in advance to take a hypothetical three- or four-hour trip. As your day approaches, see if the trip could have been made leaving either a day earlier or later than the target.

As usual, there is always some fine print. There are diminishing returns to this practice if the window options are too short, such as a quick weekend getaway where you really have to be out and back within two days. It also won’t work if you “have to be somewhere” or “have to get back to work.”

When flying light GA, that puts impossible pressure on fools to rush in where angels fear to tread. Let’s also acknowledge that there is almost always some cost involved when things don’t go as planned. That might mean an extra night in a hotel and more pet/plant/kid-sitting expenses. If you’re going to travel by light GA that’s a reality but, come to think of it, the same applies at certain times and hubs with the airlines.