The Dos and Don'ts Of Mountain Flying  




The Dos and Don'ts Of Mountain Flying  

Some of the following DOs and DON'Ts of mountain flying have been extracted from the Department of Transportation book AC91-15, "Terrain Flying." These deserve careful consideration by any pilot who plans to conduct flight operations in mountainous country. An experienced pilot having many flight hours of flying time may be inexperienced in mountain flying and unfamiliar with these age-old rules and guidelines. If you are a transient pilot, land at an airport away from the mountains and talk to the local pilots or the Accident Prevention Counselor in that area to find how best to get to your destination.

Arrange the flight to avoid topography which would prevent a safe forced landing. Maintain sufficient altitude at all times to permit gliding to a reasonably safe landing area. Plan the flight along routes that include populated areas and well known mountain passes. Sectional charts are much better than World Aeronautical Charts (WAC) for details. Study them thoroughly for altitude over the route and for obvious checkpoints. Prominent peaks often make good checkpoints. Watch for compass irregularities in areas of local magnetic disturbance, usually  marked on charts.


Magnetic disturbance can vary from 0 to 47 degrees. Don't fly light aircraft when the winds aloft at your proposed altitude are above 20 to 25 knots. Expect wind to be much greater velocity over mountain passes than reported in areas a few miles away. Know your wind direction at all times. Compare it to water as it flows up, over, and down the mountain ranges. Look for smoke, dust, and shadows of clouds on the ground to aid in determining wind direction. Watch for abrupt changes of wind direction and velocity in the mountains. Don't fly near or above abrupt changes of terrain such as cliffs or rugged areas. Very dangerous turbulence may be expected, especially with high winds. Don't fly up the middle of a canyon at any time. It is better to fly along one side or the other so that you will be in a better position to execute a 180-degree turn. Also, never fly so far up the canyon that a downdraft might trap you. Don't get excited if you get in a downdraft. It will usually cease, leaving enough altitude above the ground to maneuver the aircraft safely away. However, do not count on this in extremely turbulent air or in canyon areas.

When encountering a downdraft, maintain sufficient airspeed. Guard against stalling the aircraft and fly out of the downdraft immediately with full throttle. Proceed to an area of updraft or smoother air. Realize that the actual horizon is near the base of the mountains. This mistake of using the summit of the peaks as the horizon will result in the aircraft being placed in an attitude of constant climb.This could inadvertently lead to stall from which a recovery may be impossible.

Approach mountain passes with all the excess altitude possible. Downdrafts as much as 1,500 to 2,000 feet per minute may be encountered on the leeward side. Approaching the passes over a ridge will reduce this effect considerably. A clearance of 1,500 to 2,000 feet is preferred on windy days.  Expect winds above 10,000 feet to be prevailing westerlies in most western state areas.  Approach passes and ridges at a 45 degree angle so that, if necessary, you need only turn 90 degrees to the lower terrain instead of 180 degrees. Many experienced pilots advise that an inexperienced pilot who plans to land at a high altitude field should make a power approach and a power wheel landing. This procedure is definitely advisable in gusty air. Check density altitude before departing.

When parking aircraft on sloping terrain, be alert to the possibility of fuel siphoning overboard. It may be necessary to place the fuel selector in the "off" position when the aircraft is parked or tied down. When taking off into the wind in a narrow canyonwith several sharp bends, downdrafts may be encountered without warning. Always check your ELT (First five minutes past any hour.) to ensure it is operational. Often, pilot reports are the only reports you get in the mountains.

Denver Flight Watch (122.0) actively solicits and disseminates reports from pilots flying in the mountains. Monitor 122.0 for current reports.

Density altitude is a crucial criterion that determines the performance capabilities of an aircraft. Air density decreases with altitude. As air density decreases, density altitude increases; hence, the molecules of air decrease which means there will be less air flowing over the camber of the wing. The further effects of high temperature and high humidity are cumulative, resulting in an increasing high density altitude which reduces all aircraft performance parameters. In density altitude, Weight & Balance is another important consideration. For instance, consider the following two scenarios:

1.If the CG is set to the aft position, a stall would be impossible to recover from and may result in a spin.

2.If the CG is set to the forward position, a stall will be encountered at a higher than normal stall airspeed configuration.

Density altitude is the altitude at which the aircraft thinks it is and performs accordingly.

CHECK YOUR DENSITY ALTITUDE! Add a checklist prior to flying in the mountains that includes the following:

1.Density Altitude Calculations


3.Performance charts

4.Weight & Balance

Be certain you re aware of proper fuel mixture settings for your type aircraft. Full power leaning may be necessary for takeoff and landing procedures with normally aspirated engines. Most turbocharged reciprocating engines require full rich mixture prior to takeoffs and landings. Check your Flight Manual or Pilot Operating Handbook (POH).

There may be occasions when it will be necessary to climb to an altitude where oxygen is required by regulation. Portable oxygen comes in very handy at these times. Review FAR 91.211. Additionally, be aware that your body may need supplemental oxygen before the FAR's require it.

Enrich mixture slightly before landing so that power will be available for a go-around.

Very seldom is a flight in mountainous areas purely routine--learn to expect the unexpected.

Remember that you, the pilot, have complete responsibility for the Go/No-Go decision based on the best information available. Do not let compulsion take the place of good judgment-know you can go, or stay on the ground.
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