Flight Training - March 2019 - 45

ADVANCED PILOT ACCIDENT ANALYSIS

FROST-FREE FLIGHT

SOME OF THE MOST DANGEROUS AIRFRAME ICING HAPPENS BEFORE TAKEOFF
BY DAVID JACK KENNY

LAST MONTH'S DISCUSSION OF ICING HAZARDS MADE ONLY A PASSING MENTION OF

frost. Blame that on space constraints. Since frost usually forms on the ground, it
doesn't seem as intimidating as ice accumulating while airborne-but its effects in
degrading aircraft performance can be just as sinister, and every machine parked on
the ramp when temperatures near the freezing point is potentially exposed to them.
Thank the fact that most aircraft don't fly on any given day for frost contamination not
contributing more conspicuously to the accident record. As it is, about one-quarter of
all icing accidents in airplanes are caused by the disruptive effects of frost (or snow)
that should have been removed before takeoff.
Unlike in-flight icing, frost doesn't change the shape of an airfoil, but its granular surface disrupts the smooth flow of air assumed by both aircraft designers
and certification standards. Remember your introduction to aviation meteorology? It included the FAA's admonition that: "Roughness, similar to medium
sandpaper, on the wing's leading edge and upper surface can reduce maximum
lift by as much as 30 percent and increase drag by 40 percent." This can leave
even a lightly loaded airplane that would otherwise have an ample performance
margin unable to climb out of ground effect-a fact that may not become apparent
to the pilot in time to abort.
A Grumman American AA-1 Yankee crashed less than 3 miles from the departure end of the runway after its solo pilot neglected to defrost its exterior. His
departure path was toward a line of hills the airplane normally cleared without difficulty. A Cessna 182 floatplane taking off from a lake with two on board
couldn't get into the air before reaching the far shore, sliding "along a gravel
spillway for several hundred feet before nosing over." The pilot acknowledged
having done a less-than-perfect job of clearing frost from the wing's upper surface, an admittedly difficult task on a high-wing airplane sitting even higher on
straight floats.
It's not necessary for the entire aircraft-or even the entire wing-to be contaminated for performance to take a significant hit. A TBM-700 that attempted
to take off in a snowstorm was brought down by lumpy ice that only formed over
the fuel tanks-the cold airplane had been given fuel from a truck kept in a heated
hangar, causing snow that otherwise would have blown off the skin to melt and
then refreeze. And while cleaning the wings but not the fuselage recovers the lost
lift, increased drag still saps performance and increases stall speeds throughout
the flight envelope.
In a perfect world, every aircraft would come with its own hangar. In the one
we inhabit, parts and mechanics' time are expensive-and deicing, while costly,
can still be cheaper than trying to do without. FT
DAVID JACK KENNY is a statistician and freelance aviation writer.
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Flight Training - March 2019

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