Relative humidity concern could ground GA planes

Citation

(2007), "Relative humidity concern could ground GA planes", Aircraft Engineering and Aerospace Technology, Vol. 79 No. 2. https://doi.org/10.1108/aeat.2007.12779bab.020

Relative humidity concern could ground GA planes

Relative humidity concern could ground GA planes

A new interpretation of what “known icing conditions” really means could ground general aviation aircraft for the winter, according to the Aircraft Owners and Pilots Association.

The new interpretation, handed down from the FAA's Eastern Region counsel, says that “high relative humidity” constitutes known icing conditions. This means that in high relative humidity conditions when the temperature is near or below freezing, pilots must fly an aircraft with deicing equipment. Many light GA aircraft are not equipped for flight into known icing conditions.

“This overly restrictive interpretation of `known icing conditions,' if literally applied, would unnecessarily ground many safe general aviation flights and may negatively affect safety because many pilots would not be able to train nor maintain flying proficiency during the winter season,” wrote Luis Gutierrez, AOPA Director of regulatory and certification policy, in a letter to the FAA.

Gutierrez requested the FAA Eastern Region's letter of interpretation be rescinded.

AOPA points out this restrictive interpretation is not consistent with other FAA publications – not the least of which is the aeronautical information manual – which state that visible moisture, along with freezing temperatures, is necessary for structural icing in flight. High relative humidity is not visible.

The association further explained that relative humidity is not included in FAA or National Weather Service aviation weather reports or forecasts.

“So how are pilots to know when high relative humidity would be a factor to their flight,” Gutierrez challenged the FAA, “and how are pilots expected to know what constitutes high relative humidity since this is not defined anywhere?”

The FAA's previous definition of known icing conditions was objective, quantified, and based on meteorology, Gutierrez said. AOPA believes this new definition – which could shut down an entire segment of the GA industry for four months out of the year – is subjective, is not scientifically proven, and should not be accepted.