EAA Sport Aviation - December 2010

but there are situations of which we should already be aware. While icing can occur any time visible moisture and freezing temperatures prevail, some conditions are more likely to result in ice formation (see table below). An air mass that passes over a large body of relatively warm water can be loaded with moisture and is likely to cause icing. Icing is also common along fronts and in areas of low pressure. Don’t think that “out of the clouds” translates to “no danger of icing.” Where a cold front drives a wedge beneath warmer air, rain can fall into colder air beneath, resulting in the most dangerous conditions: freezing rain or drizzle.

Remember, too, that even when flight is possible above the clouds or between layers, an instrument approach or unplanned descent or climb could put us squarely in the danger zone. Once caught in the icing trap, it might be too late to get out.

CAUGHT IN THE TRAP

Consider the certificated commercial pilot of a Lancair IV-P and his passenger flying VFR from Page Field (FMY) in Fort Myers, Florida, to Hartford-Brainard Airport (HFD) in Connecticut. The pilot had not received a proper preflight weather briefing and was unaware of the dangers ahead. Two and a half hours into the flight, the pilot requested an instrument flight

White or milky in appearance, rime ice commonly coats the leading edge of wings, control surfaces, and propellers.

ICING RISK

High Medium Low

CUMULUS CLOUDS

32° to - 4° (F)

- 4° to - 40° (F)

Below - 40° (F)

rules clearance and was cleared from

17,500 feet down to 17,000 feet. According to the National Transportation Safety Board (NTSB) report, he called air traffic control (ATC) four minutes later and asked for a lower altitude due to icing. ATC told him light rime icing was reported between 15,000 feet and 12,000 feet. Another aircraft reported no icing at 11,000 feet, so a hasty descent seemed prudent.

ATC cleared the Lancair to 15,000 feet and said a lower altitude would require vectors around climbing traffic. By that time, the situation was already desperate. The Lancair disappeared from radar and slammed into terrain in Snow Hill, North Carolina. The aircraft was destroyed, and the pilot and his passenger were killed.

Conditions were rife for icing that
afternoon. The NTSB report revealed that
“level 1 weather radar returns and
recorded temperatures aloft of - 3 to - 7
degrees Celsius indicated that super-
cooled large water droplets were most
likely present in the area. The accident
airplane most likely encountered moderate
to severe clear or mixed icing while
descending out of 17,000 feet.”
This tragic accident highlights some
clear lessons about icing. First, due diligence
is needed to identify the potential for icing
conditions. Failure to get a weather briefing
can be a fatal mistake.

Just as important is recognizing the critical nature of an icing encounter. When an aircraft without de-icing capability enters severe icing conditions, action must be taken immediately. This is no time to be polite and patient. Declare an emergency and get out of the ice immediately.

Even minor amounts of ice can have serious safety implications. It doesn’t take much ice to block unheated pitot/static systems, causing erroneous airspeed and altitude readings, or no readings at all. The upshot is often a stall or entry into an unusual attitude, leading to a loss of control.