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.)
TAKEOFF
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.
EN
ROUTE
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.
DESCENT
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.
LANDING
·
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.
POST
FLIGHT
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!
FLY SAFE!