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All pilots, regardless of qualifications and amount of flight experience, know that Mother Nature rules the skies and has a nasty temper. She snarls at us in the form of wind, clouds, fog, rain, hail, snow and ice, turbulence, and lightning. Each of these weather hazards can ruin a pilot’s day in a heartbeat, and we are taught that whenever possible, avoidance is always the best tactic in dealing with them.
Absent an instrument rating and an airplane equipped to fly safely in the clouds without a visible horizon, avoidance typically means don’t fly today. Commercial pilots, however, have a job to do and are trained to deal with what we call instrument meteorological conditions (IMC). We can enter the clouds and areas of low visibility by reference to instruments that allow us to “keep the shiny side up,” a reference to the fact that the bottom of an airplane is usually dirtier than the upper surfaces. Many private pilots have instrument ratings as well, because it allows them to fly in less-than-ideal weather conditions and provides enhanced travel flexibility.
No matter what pilots want the non-aviator to think, none of us has x-ray vision, and clouds look exactly the same whether or not we have an instrument rating. What might be waiting behind the curtain is the problem, and pilots of large commercial aircraft deal with that uncertainty by using on-board color-weather doppler radar.
This technology detects water in the air, and more importantly, the amount and movement of the water, and displays the area of weather in front of the aircraft with green, yellow, orange, red, and magenta to indicate the intensity of the hazard.
Without turning this post into a meteorology lesson, suffice it to say that all the violent weather on the planet uses water for fuel and results from the collision of two (or more–ever heard of Hurricane Sandy?) air masses with different temperature, barometric pressure, and humidity.
Not so long ago, the only way a pilot in an aircraft without on-board weather radar could determine the potential dangers ahead inflight was to contact an air traffic controller or weather specialist on the radio. The typical description might be something like:
“From 40 miles north-northeast of the Stonewall VOR to 50 miles east of the Centex VOR to 20 miles northeast of the Humble VOR to 30 miles southwest of the San Antonio VOR an area of level 4 and 5 thunderstorms moving northeast at 35 knots with tops to 45,000 feet.”
Try copying that down, much less plotting it on a map or interpreting it in your brain.
Enter one of the most significant advancements in weather-avoidance technology for smaller airplanes: satellite weather images right there in front of you on a screen, that can also display your planned course line, navigation aids, airports, etc. How in the world do they do that?
The process uses images from a number of satellites in geosynchronous orbit to create a composite image, which is then transmitted to an antenna on the aircraft for display in the cockpit. No more dealing with a word-salad description of the storms. It’s right there on the instrument panel, so the pilot can turn to avoid the weather and navigate around it.
I’ve inserted a link at the end of this post to an excellent video produced by the Air Safety Institute, a division of the Aircraft Owners and Pilots Association. This case study vividly illustrates the potentially tragic effect of time lapse.
Unlike real-time on-board color-weather radar displays, satellite weather information is always a delayed snapshot. Display screens are designed to give the pilot an indication of how old the image is by providing a count-up timer, which tells you how long it’s been since the image was uploaded to your screen, not since the data was collected.
This may seem to be a limitation that renders the data useless, but in reality, satellite weather is an essential tool so long as pilots take time lapse into account. This case study documents the circumstances surrounding an encounter with violent weather that killed the pilot and passengers of a Cherokee Six that went down over southeast Texas in late 2011.
This is not a story of pilot incompetence, or lack of training, or failure to maintain currency. It does, however, indicate questionable judgment and the possible effect of a condition that pilots call get-home-itis. I’m speculating, but why else would a pilot elect to continue toward his final destination after a long day of flying, at night and in bad weather that included a monster area of thunderstorms? The answer to that question also has to include confidence in his ability to avoid the storms using on-board satellite weather data. He had no intention of flying into dangerous weather, which is exactly what he did.
Seven critical factors form the links in the chain of events.
- The area of weather was moving from the southwest at about 45 knots (52 mph).
- The Cherokee Six cruises at 135-155 knots depending on the power setting.
- The pilot had skirted the area of weather to the southeast and had turned back to the west to get behind the storms for a landing at his destination.
- Against a significant headwind, his speed over the ground had dropped to less than 100 knots.
- The weather data had appeared on his display over 8 minutes before the accident.
- Time lapse had considerably aged the data to further reduce its currency.
- In 8 minutes plus the time lapse, the storm could have moved as much as 10 miles.
In the final analysis, the pilot mistakenly thought he had safe clearance from the storm, and he flew into an area that would have been colored magenta if the data on the screen had been more current. Turbulence subjected the Cherokee to aerodynamic loads in excess of structural limits and snapped off a wing.
Of all the hazards to aviation Mother Nature can place in a pilot’s way, a thunderstorm’s hammer is without question the most dangerous. For an in-depth view of how this tragedy unfolded, click on the link below. It contains analysis, radar tapes showing the storm in relation to the flight path of the doomed aircraft, and recordings of pilot-to-controller communications.
