NTSB Safety Alerts

Fine particles of frost or ice, the size of a grain of table salt and distributed as sparsely as one per square centimeter over and airplane wing’s upper surface, can destroy enough lift to prevent a plane from taking off.

Almost virtually imperceptible amounts of ice on an aircraft wing’s upper surface during takeoff can result in significant performance degradation.

Small, almost visually imperceptible amounts of ice distributed on an airplane’s wing upper surface cause the same aerodynamic penalties as much larger (and more visible) ice accumulations.

As little as 1/4 inch of leading-edge ice can increase the stall speed 25 to 40 knots. The danger is that some 1/4-inch accumulations have minimum impact and pilots become over confident.

Sudden departure from controlled flight is possible with only 1/4 inch of leading-edge ice accumulation at normal approach speeds.

Recent NTSB investigations have identified several accidents that appear to be wholly or partly attributable to in-flight encounters with severe weather.

These accidents have all involved aircraft operating under instrument flight rules and in contact with air traffic controllers.

Investigations show that pilots were either not advised about areas of severe weather ahead or were given incomplete information.

Meteorological Evaluation Towers (METs) are used to measure wind speed and direction during the development of wind energy conversion facilities. METs are made from galvanized tubing (or other galvanized structure) with a diameter of 6 to 8 inches and are secured with guy wires that connect at multiple heights on the MET and anchor on the ground.

Many METs fall just below the 200-foot Federal Aviation Administration (FAA) threshold for obstruction markings. They can also be erected quickly and without notice to the local aviation community, depending upon their location