Winter weather is upon us and requires extra caution. However, in both summer and winter weather is a major cause of GA accidents. Be informed, use good judgment, be safe.
- 25% of 60,000 GA accidents studied were weather related
- 35% of ALL FATAL GA accidents were due to weather
I’ve extracted highlights from a review written by Tim Vasquez, a professional meteorologist. If you want to read the 8-page article, contact me for a PDF copy: firstname.lastname@example.org.
What’s the Cause?
Low ceilings, fog, precipitation, and weather below minimums (but not icing) contributed to 69 percent of all fatal weather-related accidents. This points to VFR flight into IMC, lack of IFR training, poor situational awareness, and the need to properly use available weather information. Icing, carb ice, and density altitude contributed another 18 percent of fatal accidents.
The Weather Briefing
How you approach the briefing is actually just as important as the information. Many pilots get stuck in a go/no-go mentality, which only provides a superficial look at things. The correct technique is to take in all the information, build a full mental picture of what’s happening along your route, and from there, decide how it will impact your flight.
Be aware of the distinction between MSL and AGL. Cloud heights associated with airports are customarily given in AGL. But area guidance products, area forecasts, and PIREPs, use MSL.
Controlled flight into terrain is disturbingly common, and it happens even to highly trained pilots. Of course, accurate navigation is critical in the mountains. Any combination of significant moisture and instability always means the potential for low ceilings and visibility in mountainous terrain.
Turbulence is easily anticipated. Mechanical turbulence is linked closely to strong surface-based instability, strong pressure gradients, and speed shear and directional shear in the lowest mile of the atmosphere. In mountainous regions, a rule of thumb for moderate or greater turbulence is winds over 20 knots near the tops of mountains and ridge lines, especially perpendicular to mountain ranges.
Sudden changes usually come from the approach of outflow boundaries, which can surge outward up to 30-40 miles from a storm and produce unexpected wind shifts. Pilots can’t really second-guess gusts in the models and TAFs, but anything that strengthens the differences between the surface winds and the winds at 1000 or 2000 feet will increase your risk of gusty runway conditions.
Danger areas are near and just above the freezing level, normally -5 to +10 degrees C. The go-to tool in meteorology is the Skew-T chart. The Aviation Weather website offers easy-to-read cross-sections under their Flight Path Tool that provide not only icing potential but temperatures, giving you a clear picture of safe and dangerous altitudes.
Avoid thunderstorms. The FAA recommends remaining 20 NM outside thunderstorms. A study noted that the survivability of a GA accident in a thunderstorm is lower than 50/50.
As many NTSB reports and CVR transcripts have shown, the realization that a pilot is out of his depth usually comes swiftly and suddenly. The keys to lengthening the margin between safe flight and disaster are knowledge, experience, and situational awareness.