Tuesday, 7 November 2017
TIPS ON WINTER FLYING (PART2)
Acknowledgements: Don Hankwitz, Airport Operations Specialist
(Ed. Note: Winter is upon us again in the Northern hemisphere, so a few reminders ……cont.)
Take-offs in cold weather offer some distinct advantages, but they also offer some special problems. A few points to remember are as follows:
• Do not over-boost supercharged engines. This is easy to do because at very low density altitude, the
engine "thinks" it is operating as much as 8,000 feet below sea level in certain situations.
· Care should be exercised in operating normally aspirated engines. Power output increases at about 1% for each ten degrees of temperature below that of standard air.
• If the temperature rises, do not expect the same performance from your aircraft as when it was operated at the lower density altitudes of cold weather.
• Use carburettor heat as required. In some cases, it is necessary to use heat to vaporize the fuel. Gasoline does not vaporize readily at very cold temperatures. Do not use carburettor heat in such a manner that it raises the mixture temperature barely to freezing or just a little below. In such cases, it may be inducing carburettor icing. An accurate mixture temperature gauge is a good investment for cold-weather operation. It may be best to use carburettor heat on take-off in very cold weather in extreme cases.
· If your aircraft is equipped with a heated pitot tube, turn it on prior to take-off. It is wise to anticipate the loss of an airspeed indicator or most any other instrument during a cold weather take-off - especially if the cabin section has not been preheated.
· During climb-out, keep a close watch on head temperature gauges. Due to restrictions (baffles) to cooling air flow installed for cold weather operation and the possibility of extreme temperature inversions, it is possible to overheat the engine at normal climb speeds. If the head temperature nears the critical stage, increase the airspeed or open the cowl flaps or both.
Weather - Weather conditions vary considerably in cold climates, so don't be lured into adverse weather by a good pilot report; one pilot may give a good report and five or ten minutes later VFR may not be possible.
· Mountain flying and bad weather don't mix. Set yourself some limits and stick to them.
· On entering a snow shower, the pilot may suddenly find himself without visibility and in IFR conditions. Snow showers will often start with light snow and build.
· A "whiteout" is where there are no contrasting ground features, and whiteout can occur in good visibility conditions. It calls for an immediate shift to instrument flight. The pilot should be prepared for this both from the standpoint of training and aircraft equipment.
Carburettor Ice - In general, carburettor ice will form in temperatures between 0-10°C when the relative humidity is 50% or more. Three categories of carburettor ice are:
• Impact ice formed by impact of moist air on air-scoops, throttle plates, heat valves, etc. Usually forms when visible moisture such as rain, snow, sleet, or clouds are present.
• Fuel ice forms at and downstream from the point that fuel is introduced when the moisture content of the air freezes as a result of the cooling caused by vaporization.
• Throttle ice is formed at or near a partly closed throttle valve. The water vapor in the induction air
condenses and freezes as the air passes the throttle valve.
· A carburettor air temperature gauge is extremely helpful in keeping the temperatures in the carburettor in the proper range. Partial carburettor heat is not recommended if a CAT gauge is not installed.
· Partial throttle (cruise or descent) is the most critical time for carburettor ice. It is recommended that carburettor heat be applied before reducing power and that partial power be used during descent to prevent icing and overcooling the engine.
Carbon Monoxide Poisoning - Don't count on symptoms of carbon monoxide to warn you: It's colourless,
odourless, and tasteless although it is usually found with exhaust gases and fumes. If you smell fumes or feel any of the following symptoms, assume that carbon monoxide is present; sluggishness, warmth, tightness across forehead followed by headache, throbbing, pressure at the temples and ringing in the ears. Severe headache, nausea, dizziness, and dimming of vision may follow. If any of the above conditions exist, take the following precautions:
• Shut off the cabin heater or any other opening to the engine compartment.
• Open a fresh air source immediately.
• Don't smoke.
• Use 100% oxygen if available.
• Land as soon as possible.
• Be sure the source of the contamination is corrected before further flight.
Spatial disorientation – This can be expected any time the pilot continues VFR flight into adverse weather
conditions. Flying low over an open body of water during low visibility and a ragged ceiling is another ideal
situation for disorientation.
Engine Operation - During descent there may be a problem of keeping the engine warm enough for high power operation, if needed. It may be desirable to use more power than normal, which may require extension of landing gear or flaps to keep the airspeed within limits. Carburettor heat may also be necessary to help vaporize fuel and enrich the mixture.
Blowing Snow and Ice Fog - Blowing snow can be a hazard on landing, and a close check should be maintained throughout the flight as to the weather at destination. If the weather pattern indicates rising winds, then blowing snow may be expected which may necessitate an alternate course of action. Ice fog is a condition opposite to blowing snow and can be expected in calm conditions. It is found close to populated areas, since a necessary element in its formation is hydrocarbon nuclei such as found in automobile exhaust gas or the gas from smoke-stacks. Both of the above conditions can form very rapidly and are only a few feet thick and may be associated with clear en-route weather. A careful check of the forecast, actual weather, and cautious pre-flight planning for alternate courses of action should always be carried out.
· A landing surface can be very treacherous in cold weather operations. In addition, caution is advised regarding other hazards such as snow banks on the sides of the runways and poorly marked runways. Advance information about the current conditions of the runway surface should be obtained.
· If it is not readily available, take the time to circle the field before landing to look for drifts or other obstacles. Be aware that tracks in the snow on a runway do not ensure safe landing conditions. Often snowmobiles will use runway areas and give a pilot the illusion that aircraft have used the airport and the snow is not deep.
Ski Wheels - Ski wheel combinations are popular and very convenient; however, forgetting to use the landing gear appropriate to the runway surface can be embarrassing!
Skis - In level flight, due to their relatively dirty profile, skis will cut cruising speed to some extent. In addition to some loss of aerodynamic efficiency, skis have other disadvantages.
· They require more care in operating because bare spots must be avoided to keep from wearing the bottom coating of the skis, although the bottom coating must be renewed on some skis periodically. There is now an anti-friction tape that is very useful for this purpose. Skis equipped with the anti-friction coating do not freeze to the surface like those that expose bare metal to the snow.
· Another method of keeping skis from freezing to the snow is to taxi the aircraft up onto poles placed across and under the skis. This prevents them from touching the snow for most of their length.
· Extra care in use of skis during take-off and landing is also recommended. Rutted snow and ice can cause loss of ground control, even failure of skis or landing gear parts. Deep powder snow can adversely affect ski operation. Prolonged take-off runs in deep powder are expected and it may be deep enough that no take-off is possible under existing conditions. In this case, experienced operators taxi back and forth until an adequately packed runway is available.
The following are a few items to consider before leaving the aircraft after the flight:
• As soon as possible fill the tanks with the proper grade of clean aviation fuel, even if the aircraft is going into a heated hangar.
• If the aircraft is to be left outside, put on engine covers and pitot covers.
• If the weather forecast is for snow or "clear and colder," put on rotor, or wing covers and save yourself
from a snow or frost removal job in the morning.
• Control locks or tied controls are suggested if the aircraft is left outside, and there is a chance of high
wind conditions. Tie downs are, of course, also suggested in high winds.
• If the aircraft is equipped with an oil dilution system, consider the advisability of dilution of the engine
oil. If you decide to dilute, the manufacturer's recommendations should be carefully followed commensurate with the temperature expected.
• During engine shutdown, a good practice is to turn off the fuel and run the carburettor dry. This diminishes the hazard of a fire during preheat the next morning.
HAVE A GOOD WINTER FOLKS!