The disappearance of an Air France jet that hit a patch of thunderstorms and lightning over the Atlantic Ocean Sunday night raises questions about the aviation threats that natural hazards pose and just how dangerous they are.
Air France Flight 447 left Rio de Janeiro heading for Paris Sunday carrying 228 people, according to news reports.
The last contact with the plane came just after it hit a rough patch of weather and signaled a possible electrical malfunction, Brazilian officials said.
Some officials have said a lightning strike could have disabled the plane. That would be a rare incident, though there are several other weather phenomena that pilots must be wary of.
Following are some of these hazards, with an idea of just how much risk they hold for millions of flights around the globe each year:
A handful of jets have been blown up by lightning, including a Pan American flight in 1963 that killed 83 people. But radar and other improvements in weather forecasting now make thunderstorms — and their lightning — easier to avoid.
In the early 1980s, NASA flew a jet into a thunderstorm on a test. It was hit 72 times in 45 minutes and gave scientists valuable data.
Commercial planes are still hit about once a year, research from the University of Florida has shown.
A strike typically starts at a wingtip, nose or tail and courses through the aircraft's skin, which is often made of aluminum — a good conductor.
Many strikes are initiated by the plane itself, and most occur during the climb to cruising altitude or descent and when the plane is in a cloud.
The plane's lights might flicker, but most of the energy just heads back into the sky if there are no gaps in the aircraft's skin.
Modern jets often employ advanced composite materials, which are not so conductive.
Turbulence is a more common problem — almost all airline passengers have likely experienced a bumpy ride at some point.
Turbulence is air movement that normally cannot be seen and often occurs unexpectedly.
It can happen because of changes in air pressure, jet streams, waves created by the influence of mountains, cold or warm fronts and thunderstorms. It can even occur when the sky is clear.
Turbulence can't always be predicted and radar can't detect it.
Turbulence is the leading cause of non-fatal in-flight injuries, according to the U.S. Federal Aviation Administration, usually because passengers or crew aren't wearing seatbelts.
While turbulence may cause you to knock your head hard, it isn't likely to be fatal. From 1980 through June 2004, U.S. air carriers had 198 turbulence accidents, resulting in 266 serious injuries and three fatalities, according to the FAA.
Thunderstorms pose a risk to planes during the stormy summer season.
In general, the risk posed by thunderstorms is from the convective motion of the air within them, the powerful updrafts and downdrafts that can push a plane around, potentially damaging it or worse. (These drafts are one of the stronger forms of turbulence.)
There are dedicated forecasters who send minute-by-minute weather information to aircraft to help them avoid hazardous weather.
Air traffic controllers also keep an eye on the weather in their area, to help in their effort to guide incoming and outgoing planes.
Radar can detect rotating air in storms which can indicate the potential presence of tornadoes.
In the winter, ice on the wings of planes can pose a significant risk (and a source of flight delays).
Icing occurs when supercooled water drops adhere to an aircraft wing and freeze (supercooled drops are liquid even though the temperature is below 32 degrees Fahrenheit).
When ice builds up on the wings of an aircraft, it can simultaneously slow velocity and decrease lift, potentially sending a plane into a catastrophic dive, according to the University Corporation for Atmospheric Research.
Wing icing, which can occur in the air or on the ground as a craft waits for takeoff, has been the cause of many fatal aircraft crashes, including some involving airliners, though it is more of a hazard for commuter aircraft and other small planes.
Icing causes dozens of accidents per year with smaller craft, a study by the National Transportation Safety Bureau found.
An estimated 819 people died in accidents related to in-flight icing from 1982 to 2000, with most accidents occurring between the months of October and March, according to the same study.
In-flight icing downed the small plane carrying rock 'n' roll legends Buddy Holly, Ritchie Valens, and The Big Bopper when their plane crashed soon after take-off from Mason City, Iowa, on February 3, 1959.
Different substances can be applied to plane wings to de-ice them before takeoff.
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