The title is a little deceptive, as it's always on the ground that people die, as a result of a plane being unable to keep flying due to ice. But in my recent research on airline accidents, I've run across ice as a serious cause of airplane accidents. It turns out that there are at least three ways that ice can cause a plane to crash, all of them preventable, and mostly through designing--and correctly applying (that's the hardest part)--a mechanical solution to the problem.
1. Carb Ice: This is ice that builds up in the carburetor of a piston-powered small plane due to the cooling that air experiences as it passes through it. Just as water drips off the cooling coils of an air conditioner or freezer--becoming ice if things aren't working right--the wrong combination of humidity and altitude can easily cause a carburetor to ice up, starving the engine of air and causing it to lose power. Although this problem is easily prevented by applying heat to the air going into the carburetor, and all student pilots are rigourously drilled on the process, new pilots can become inattentive enough that carb ice continues to cause dozens of engineless landings a year, at least one or two of which, on average, are fatal.
This is not to be confused with the serious problem of water in the fuel entering and choking off a piston-driven engine, which also happened in the early days of aviation, resulting now in the highly pollutive regimen of drawing a sample of dyed aviation fuel from the low points of the fuel system and throwing it out on the tarmac after acertaining that it doesn't contain any water.
2. Rime Ice: This is ice that builds up on the leading edge of the wing, either from a plane sitting too long on the runway during an ice storm, or from flying through icing conditions in the air. Airline pilots are just as susceptible to rime ice as students pilots are--if not more so, as student pilots are warned to stay away from icing conditions, while airline pilots frequently fly through them anyway. But when they do, the results can be extremely deadly, resulting in a loss of lift that usually kills everyone on board--unless it happens on takeoff, especially if the plane comes down in a river, as did USAir Flight 405. Two methods have been developed to combat the buildup of rime ice: De-icer that is sprayed on the wings of planes awaiting takeoff in an ice storm, and either heaters or expanding rubber boots in the the wing that keep ice from being able to build up. In one case, that of American Eagle Flight 4184 (which was twice ordered to fly a holding pattern in icy conditions), the entire wing of that type had to be redesigned to avoid rime ice from coming loose and damaging the control surfaces on the tail.
3. Engine ice: This is the most insidious way that ice kills, and almost exclusively happens with airliners, because in order to get ice in the engine one either has to be flying a plane whose wings tend to shed huge slabs of rime ice into the rear-mounted engines, or flying a plane through a hailstorm, where the hail going into the engines is so heavy that they flame out, or even suffer catastrophic turbine failure. This can only happen, in the case of hail, when a pilot takes his plane into the heart of a thunderstorm, as did the pilot of Garuda Flight GA421.
Why, you wonder, would a pilot do this? Well, hopefully this will never happen again, given the dozens who have died so far, but in the early days of weather radar in airliners there was an unfortunate phenomenon in which the weather radar could only pick up rain--not hail--so on the radar what appeared to be a clear path through the thuderhead was in fact its most dangerous part, as any pilot who ever tried taking that "path through the storm" soon found out, when all his engines failed and his plane fell out of the sky. The most tragic example of this would be Southern Airways Flight 242, in which the powerless plane, minutes before crashing into a petrol station in a small town, glided right over an airport without realizing it (because neither pilot ever bothered to check their flight charts, and the passenger on board who knew about the airport didn't realize that the pilot was trying to make a much more distant air base that he was familiar with).
This is not to be confused with a jet engine running rough due to flying through high-altitude ice crystals, which so far has't caused any crashes or fatalities, as there is plenty of time for the engines to recover as the plane falls below the ice layer.
One adage of aircraft accident investigations is that every crash makes flying safer. After the earliest pilots started getting killed by carb ice, carb heat was invented to prevent it from building up. After airliners started going down with rime ice, de-icing processes and procedures were invented to prevent it from building up--and redesigned after it did so anyway. And after the extensive investigations that were required to reconstruct the accidents in which engine ice killed (as it always did), weather radars were reprogrammed, and pilots trained, to keep planes from flying into the heart of a thunderstorm.
But there is one more way that ice can kill, although it's possible that it never will, because it's only caused a crash one time--and as a result of the extensive investigation into how it was able to happen, the system that allowed it to happen was redesigned. Here's how it went down: A Boeing 747 (British Airways Flight 38) crossing Siberia after departing Beijing developed frozen water vapor in its fuel tanks, which as long as the throttles were held steady was able to build up without being dislodged. As it came in to land in London, there was turbulence, so the pilot decided to allow the plane's computer to make the approach, as it was able to adust the power level more precisely than the pilot could. As a result, the autopilot demanded a surge of power which dislodged the ice and sent it crashing against the fuel heater at the end of the fuel line, clogging it and starving all four engines simutaneously, causing the plane to crash-land short of the runway--but, due to the extreme skill of the aircrew in making a landing that they had never trained for, without any fatalities.
What the investigators finally realized (and only after it happened again, but in a 747 that was still at altitude, so there was time to allow the ice to dissapate as it descended) was that tiny projections on the fuel line heater held the ice just short of where it could be melted; all that was required was redesigning the fuel line heater, which of course should have been made that way in the first place. And, since this has only ever happened in 747's--thus it was only their fuel systems that were redesigned--it's possible that any plane flying through extremely frigid and humid air may be the first of its type to experience it.
