Mountain flying presents high risk. Never fly in the mountains without extensive pre-flight planning and a thorough weather briefing. Here are some rules of thumb derived from Tips on Mountain Flying published by Transport Canada, Aviation Safety:
- Flight routing should be arranged to avoid topography that could prevent a safe landing.
- Flight routing should be along populated areas and well-known mountain passes.
- Sufficient altitude should be maintained at all time so as to enable a power-off glide to a safe landing area.
- VFR Navigation Charts (VNC) should be used rather than World Aeronautical Charts (WAC) as they provide greater detail for air pilotage; the routing, including ground clearances, should be carefully studied before flight.
- When faced with a sea of mountains, believe your compass (bearing in mind compass irregularities) as it may be your only means of getting out of trouble.
- Do not fly when the winds are at or below mountain peak level, or at your intended cruise altitude, are above 30 KTS. Winds above 20 KTS should be avoided.
- In anticipation of possible down drafts, always cross a mountain ridge at a 45° angle so as to allow a turn away from the ridge.
- Know the wind direction at all times, and be on the look out for changes in wind direction and velocity.
- Never fly in the vicinity of abrupt changes in the terrain, such as cliffs or ridges as they can be associated with severe turbulence.
- In anticipation of downdrafts and severe turbulence, cross mountain ridges at maximum altitude, and never with less than 1500’ separation.
- Anticipate downdrafts on the leeward side of mountains, and updrafts on the windward side; anticipate downdrafts between 1500’ and 2000’ per minute.
- Do not panic if a downdraft is encountered; they usually cease with sufficient height above ground that will enable manoeuvring safely away. Do not count on this, however, in extremely turbulent air or in canyon areas.
- If you encounter a severe downdraft, use full power and maintain the best rate of climb speed for the altitude at which you are operating; being cautious of the stall speed, attempt to fly to an updraft or smooth air.
- Remember that the actual horizon is near the base of distant mountains; improperly using the mountain peaks as the horizon will place the aircraft in a slow-flight attitude unable to climb.
- Never fly up the middle of a canyon; instead, fly along one side or the other in case a 180-degree turn is required.
- If possible, fly up the right side of a canyon in anticipation of other aircraft flying in the opposite direction.
- Beware of flying up canyons, valleys, and passes where the rise in terrain could exceed an aircraft climb capability.
- Beware of flying below a cloud ceiling in mountain passes—while the cloud base could be constant, the distance between the cloud base and the ground could decrease owing to rising terrain.
Additional Readings:
Transport Canada's Tips of Mountain Flying Part I
Transport Canada's Tips on Mountain Flying Part II
Transport Canada's Looking Back: Flying into a Mountain Trap
