Horizons Online Edition

Issue date: 9/14/06 Section: News

While the ever-changing scenery, and the clean, high altitude air are some of Prescott's finest attributes, these factors can create some hazards when it comes to flying. Keep in mind that we do not teach mountain flying at Embry-Riddle. What we do teach, and the purpose of this article, is how to avoid the dangers associated with mountain flying.

The number one rule is to always keep yourself in a position that allows you to turn towards lower terrain. This means staying at an altitude that gives you adequate clearance from rising terrain.

If on a cross country, or even when just on a local flight in the practice area, pick as high a cruising altitude as feasible and if possible avoid locations that are rugged and have sharp terrain change. In case of an emergency such as an engine failure, this will give you the greatest amount of time to select your best option for a safe forced landing.

It will also give you a greater safety margin for another almost certain, but usually invisible hazard. In addition to the lifting action of our active monsoon season and the bumpiness of those warm afternoons, abrupt changes in terrain can cause severe turbulence.

If the winds are reported to be strong, you can expect the winds over mountains to be of a much greater velocity and can create a phenomenon known as a mountain wave. Approaching an event such as this will first be indicated by a smooth updraft, followed by a downdraft that can commonly produce 1,500 to 2,000 feet per minute descents, exceeding the climb capability of our aircraft.

Always be prepared to cope with a downdraft. It is recommended that when approaching a ridge from the downwind side to approach at a 45-degree angle to permit a safer retreat if needed.

With a field elevation of just over 5,000 feet, density altitude is another major concern. Control towers and FSS will advise to "Check Density Altitude" when the temperature reaches a certain level for fields 2,000 feet and higher in elevation, and for good reason. With an increase in altitude, plus the warmer temperatures of the summer, we experience a decrease in air density causing a performance loss in our engines and a reduction in propeller efficiency. Our climb rates suffer, and remember that even though we are still operating at the same indicated airspeeds, our true airspeeds will be higher, making landing and takeoff distances longer.

One last danger, although not experienced in our area very often, is mountain obscuration. Clouds, smoke, or even precipitation can cause this phenomenon. Normally not an issue for IFR flights, terrain can be obscured from view making it difficult or impossible to judge distance from the ground. VFR flights be sure to keep those cloud clearances!

If you do find yourself at low altitude either inadvertently or during an emergency, keep a few things in mind. The "turn-around point" is where you are flying towards rising terrain and come to a position about 500 feet AGL. Always make all turns away from the mountain if possible. The "point-of-no-return" is where the terrain is rising faster than the climb capabilities of the aircraft. If you are beyond this point DO NOT try to turn around, but instead land straight into the terrain ahead and DON'T STALL. The human body can withstand about 40 G's of lateral force, but only 6 to 8 G's of vertical force. The physics of trying to turn around at this point say it is just not going to work.

Do not forget to file a flight plan, and always be familiar with the area that you are going to be flying over along with what the weather for the day is going to be. With that in mind, Arizona can make for some of the best flying in the country.

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