Preflight Oversights
A pilot was flying at cruise altitude with an outside air temperature of minus 15 degrees Celsius (5 Fahrenheit) when he switched fuel tanks. As he made the switch, the fuel flow fell to zero and the engine quit. The pilot tried switching back to the main tank and turning on the auxiliary fuel pump but was unable to restart the engine. Fortunately, the aircraft was a twin, and after making an uneventful single-engine landing, the pilot found that the problem fuel tank contained more than 20 ounces of water, which the pilot had mistaken for fuel during preflight in marginal lighting.
Water in the fuel system can be a problem any time, but it can be especially insidious in cold conditions. Even small quantities of water can become ice crystals or pellets, which can quickly clog a fuel filter and starve the engine of fuel. There are ways to protect your fuel supply from ice, including adding isopropyl alcohol to your tanks. Be sure to check your airplane's pilot's operating handbook for recommendations before adding anything to your fuel system.
Perhaps more obvious is the need to remove ice, snow, and frost from the aircraft's wings, propellers, and control surfaces. When pilots omit this critical step, they put their safety and the safety of their passengers in jeopardy.
It was a beautiful morning for flying in Anchorage, Alaska. Visibility was 90 miles with a scattered layer of clouds at 6,000 feet and a ceiling of broken clouds at 12,000 feet. With an 8-knot wind from the northeast, the pilot of a Cessna 182 and his passenger started the takeoff roll on a flight to Kenai. The pilot had not removed the ice and snow from the aircraft's wings before departing. Witnesses watched as large slabs of crusted snow and ice slid from the wings during takeoff and initial climb. Because of the snow, the airplane could not maintain lift. It stalled, crashing into trees at the end of the runway. The pilot and passenger were seriously injured.
Even a thin coating of frost can disrupt the flow of air over the wings and control surfaces enough to spoil lift, as the 200-hour private pilot of a Piper Cherokee (PA-28-140) in Rawlins, Wyoming, discovered too late. It was a clear December morning with 60-mile visibility and light winds out of the southwest. The pilot attempted a takeoff on a 7,000-foot runway with a heavy coating of frost still adhering to the wings of his Cherokee. The airplane became airborne but failed to climb out of ground effect. The aircraft slammed into a 30-foot-high pile of sand 200 yards beyond the end of the runway. The pilot and passenger died in the post-crash fire.
Runway Rodeos
Safe operations require not only a clean aircraft, but a clear runway as well. It was mid-January in Louisville, Kentucky, when a 1,700-hour pilot and one passenger launched on a flight to Minneapolis in a Beechcraft A36TC Bonanza. The pilot had received a full weather briefing and filed an IFR flight plan for the trip. Unfortunately, he never made it off the ground.
The pilot began his takeoff roll on the slush-covered runway with about one-half-inch of snow clinging to the wings. The pilot had expected the snow to blow off during takeoff, but despite accelerating to a speed of between 80 kt and 100 kt he was unable to clear the wings. The pilot decided to abort the takeoff, but the slick runway confounded his efforts. The aircraft slid off the end of the runway and through a fence, coming to rest in a golf course. Although the aircraft sustained substantial damage, the pilot and passenger were not injured.
Runway conditions also are critical to landing. Snow, slush, and ice on runways mean much less traction, increasing the distance needed to stop after touchdown. Especially in gusty crosswind conditions, a slick runway can cause a pilot to lose directional control on landing. Such was the case for the pilot of a Cessna 182 and his passenger.
It was a late winter afternoon when the pilot taxied for departure on Runway 29 at Longmont Airport in Colorado. The wind was out of the west at about 20 kt, and water from melting snow had refrozen on the taxiway. As the aircraft turned, the wind caused the aircraft to slide off the taxiway and into the adjacent snow bank. No one was hurt.
Crises In Cruise
During the early afternoon on January 2 the pilot of a Piper Archer (PA-28-200) departed Zionsville, Indiana, on a flight to Athens, Georgia. The pilot had received a weather briefing that forecast possible icing but elected to fly anyway on an IFR flight plan. Instrument conditions prevailed with a 300-foot obscured ceiling and one-mile visi- bility when the pilot departed with two passengers. During the climb to cruise, the pilot lost control of the aircraft. The pilot and his passengers were killed.
The investigation revealed ice blocking the pitot/static tube. The pitot heat switch was in the Off position. Presumably, instrument failure caused by blockage of the pitot/static port led the pilot to lose control of the aircraft.
Forecast icing conditions are nothing to take lightly. Even anti-icing protection is no guarantee. Avoidance is essential.
Remember, too, that winter weather can turn on a dime, so always have an alternate plan for a winter cross-country flight. As a CFI completing a short cross-country writes in a NASA Aviation Safety Reporting System (ASRS) report, "When I left my home airport, the ceiling was 4,200 feet overcast with 10-plus miles visibility. [The destination] airport is about 10 miles away. As I got closer to [the destination], a thin scattered layer at 2,000 feet got thicker and lower. About four miles out, I saw low clouds over the airport. I immediately turned back home. I was able to continue VFR without incident.
"I was amazed by how quickly the weather deteriorated. I had received a briefing only minutes before the flight. I would not have hesitated to send a student pilot on the same flight with the information I had about the weather. A student pilot in the same situation may have pressed on with disastrous results."
Too Cool
Aircraft performance can be excellent in cold weather but human performance can suffer when the temperature gets low.
The pilot of a Cessna 172RG had departed Jefferson Country Airport in Broomfield, Colorado, one winter morning on a VFR flight to Pueblo, Colorado. Shortly after departure, the pilot realized that the cabin heater was not producing sufficient hot air. However, he was properly dressed and decided to continue the flight. On the way, he got cold, and the discomfort became a serious distraction. By the time he reached Pueblo, he was flying poorly, did not complete his checklist, and missed several radio calls. Fortunately, he made a successful landing, and he brought the aircraft to a maintenance facility to have the cabin heat system repaired.
As this pilot learned, the effects of cold extend well beyond simple discomfort. Hypothermia can severely hamper a pilot's ability to function, resulting in lethargy, sleepiness, and lack of coordination. In cold weather a heating system problem, especially a carbon-monoxide leak, should be treated as an emergency, and a precautionary landing should be made at the nearest suitable airport.
Beware the Ice
When visible moisture and freezing temperatures coexist, the potential for ice accretion also exists. Factors influencing the formation of ice include water droplet size and distribution as well as the aerodynamics of the airframe. However, several rules of thumb apply.
The most severe in-flight structural icing occurs between 0 C and minus 10 C (32 F and 14 F). Freezing rain can occur in clear skies, but icing is most likely to occur in visible moisture like clouds and precipitation. As part of your preflight planning, evaluate the cloud bases and tops with respect to the freezing level. Bear in mind that multiple freezing levels may exist, particularly near fronts.
Ice comes in five basic varieties - rime, clear, freezing rain, large-droplet, and frost - plus mixtures of the aforementioned. Rime ice is white, frost-like, and brittle. It typically forms when water droplet sizes are small, as in stratiform clouds. Air trapped within the ice gives it its milky white appearance. Rime ice often accumulates on the leading edges of wings and any number of airframe protrusions, including temperature probes, pitot tubes, antennas, and landing gear. Because it is brittle, rime ice is relatively easy to remove. Aircraft deicing equipment can often successfully remove rime ice in flight.
Clear ice forms when water droplets are larger, and this type of ice spreads out on aircraft surfaces before freezing. Clear ice forms over all surfaces, and it is much harder to remove than rime ice. Clear ice can accumulate quickly, adding tremendous weight to the airframe. It typically forms in cumuliform clouds and rain.
Pilots of aircraft not equipped with deicing systems should never attempt to fly in known icing conditions. If icing is encountered in flight, the pilot should take evasive action immediately. This may include climbing to clear air or colder temperatures, changing to an altitude where temperatures are above freezing, or turning around and flying out of the conditions. Never hesitate to declare an emergency and seek assistance if you find yourself in icing conditions. Ice can build quickly, disabling the aircraft in minutes.
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