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WHS CLASS of '65
SKYDIVE INTO BLUE HOLE -- BELIZE
DEPARTURE CHECKLIST FOR
HIGH ELEVATION AIRFIELDS
25 MOUNTAIN FLYING TIPS FOR GENERAL AVIATION PILOTS FROM EAST OF THE MISSISSIPPI*
"It is absolutely necessary in any airplane to maintain thy airspeed lest the Earth shall arise and smite thee." --Barry Schiff
The following suggestions are made for piston, non-turbocharged aircraft. Turbocharged and turbine powered aircraft will experience the same loss of control surface effectiveness as for piston aircraft when departing from high elevation airfields. A good way to test your aircraft's performance before heading for the mountains would be to fly at high altitude (>10,000' MSL) around your home airport and practice climbs, descents, and turns at various airspeeds. If you are going to be doing serious mountain flying, you should invest in a portable oxygen system for two that will allow you to freely fly between 12,000' and 14,000' -- remember there are 53 peaks over 14,000' high in Colorado.
1. Even experienced mountain pilots rarely try to fly in the mountains IFR, at night, or in bad weather (with poor visibility, high winds, or mountain obscuration). You need every "out" you can use while flying around high terrain, and fewer outs will be available under these adverse conditions. Since navigation aids depend upon line-of-sight radio transmissions, signal strength is not optimal when flying around high terrain making low altitude IFR flight difficult if not impossible in some areas.
2. When departing high elevation airfields (>6,000' elevation), if you do not reach 71% of rotation speed when you are half way down the runway, you will not have enough runway length for a safe takeoff and should abort the takeoff roll. If necessary before takeoff walk the entire length of the runway and mark the half way point with a paper cup or some other easily visible marker. Calculate your 71% rotation speed before beginning takeoff roll. Perform the T/O like a short field T/O according to your POH. A good technique is to begin T/O roll with no flaps to minimize drag, then add one notch of flaps when you reach rotation speed. After your aircraft breaks the runway surface, fly in ground effect for several seconds to pick up speed before climbing out. If your aircraft climbs at 1,000 fpm at sea level, it will probably only make half that rate from an airfield at 10,000' elevation.
3. For normally aspirated piston engines (non-turbocharged) departing high elevation airfields, the mixture needs to be leaned for maximum efficiency and power before takeoff. To determine the ideal T/O fuel mixture, always run up the engine at FULL POWER, not the recommended run up power in the POH. At the time of run up, lean the mixture until the engine RPM just begins to drop, then enrich by making two full rotations clockwise on the mixture control knob (720 deg.). Do not change this setting throughout T/O roll, climb out, cruise, descent, landing and taxiing as long as you are flying high elevation airports. If the mixture control in your A/C is a lever, while running up at maximum RPM, lean the mixture until the RPM just begins to drop, then enrich slowly until maximum RPM is achieved. Do not change that setting while flying at high altitude.
4. Consider a downhill T/O roll whenever possible when departing from high elevation airfields. If the runway is sloped as little as 1%, making a downhill takeoff roll would be like adding 10% of the length to the runway. Also when using a downhill takeoff roll, it is more likely that you will be climbing out over lower terrain. Use as little fuel as needed to reach your destination plus necessary reserve...a lighter weight A/C will rotate and climb out faster. This is no time to top off the tanks.
5. Normally aspirated (non-turbocharged) engines lose about 1" of manifold pressure for each 1,000' of elevation/altitude.
6. The minimum flap setting from your aircraft's POH is recommended for T/O at high density altitude airports to achieve best performance. NEVER use full flaps for departure from a high elevation airport -- the increased drag is more of a detriment than the gain from increased lift. It is also important not to over rotate at lift off to avoid high induced drag and poor T/O performance. The A/C should not be expected to climb as it does at sea level.
7. ALWAYS check winds aloft before flying in the mountains. High winds aloft will be greatly affected by high terrain. Winds on the windward side of ridges and mountains typically create updrafts, while winds on the leeward side of the mountain create down drafts and rotors. Winds in narrow passes and canyons are usually traveling at a much higher velocity and potentially create much more turbulence/rotors than winds in the open. Consider not flying at all if winds aloft exceed 30 knots.
8. You'd probably best avoid mountain flying altogether if your A/C has less than 160 hp or you have less than 150 hrs. total flying time.
9. Always cross mountain passes at least 1,000' above the highest terrain, preferrably 2,000'. When crossing ridge lines, approach them at a 45 degree angle and if winds are 25 knots or more, plan on at least 2,000' higher than the highest terrain. Approaching the ridge line at a 45 degree angle allows you to turn away from rising terrain if a downdraft or turbulence is encountered. Also plan to be at the crossing altitude at least 3 miles before reaching the ridge or pass. You may need to circle several times to gain altitude before attempting to cross a ridge line after climbing out from a valley airport. It is inadvisable to attempt to overfly a ridge line at or even near the service ceiling of your A/C.
10. Once you have cleared a ridge line, turn away from it at a 90 degree angle to get away from potential turbulence or rotors as soon as possible. When approaching or departing a ridge line or mountain pass, always give yourself the ability to turn away toward lower terrain quickly if necessary. No GA aircraft can outclimb a severe mountain downdraft, especially while flying at high altitudes.
11. Weather reports are usually given in reference to valley airports. These airports may be 4,000' or more lower than the mountain elevations, even in passes. Always remember...cloud heights are in reference to the surface, not MSL, so do not forget to take this into account when you are flying near a solid overcast. Even when surface visibility is 15 miles, consider staying on the ground if mountain tops are obscured by the cloud ceiling.
12. Even without mountain obscuration, if surface visibility is less than 15 miles, consider not flying...if less than 10 miles, don't go!
13. If winds aloft are greater than 30 knots at the mountain tops (9,000' - 12,000'), consider not flying.
14. Lenticular clouds are usually indicative of high velocity "mountain wave" type winds blowing perpendicular to ridge lines. These clouds are reported in aviation weather reports as ACSL (altocumulus standing lenticular) or CCSL (cirrocumulus standing lenticular). Therefore lenticulr clouds should be avoided.
15. A normally aspirated piston engine will lose about 3% of its horsepower per thousand feet of density altitude increase. In addition the wings will create relatively less lift and the propeller will be less efficient because it is an airfoil. Therefore at higher density altitudes overall performance of the A/C is affected adversely as follows:
16. The A/C should be flown at no more than 90% of its maximum rated T/O weight at high density altitude airfields. This will allow you to regain much of lost performance. Before taking off at a high DA airport is NO time to top off the fuel tanks.
17. Best rate of climb (Vy) IAS decreases as altitude increases. Best angle of climb (Vx) increases slightly as altitude increases.
18. PIREPS are very useful in mountain flying because airports are few and far between and usually not located on or near mountain tops or remote mountains. Therefore you are advised to give PIREPS often while flying in mountainous terrain -- and call FSS frequently for PIREPS reported along your route of flight.
19. For mountain flying during winter months, always check for airport NOTAMS at your destination before flying. Avoid large piles of snow along the RW's and taxiways while moving on the surface, especially in low wing A/C.
20. When flying in a valley, always fly on the side of the valley that has updrafts depending upon the winds and surrounding ridges. This is usually the side of the valley the wind is blowing toward. Never fly down the middle of a valley or canyon...you will have less room to make an emergency turn if necessary. If you are forced to make an emergency turn, always slow the A/C so you can turn in a smaller radius. Never fly up a box canyon even if you have checked topographic charts unless you have a pilot experienced in the local terrain with you. If you are going to traverse a mountain pass, always climb to your crossing altitude before entering the pass.
21. When flying in high trurbulence, do not exceed the maneuvering speed (Va) of the A/C according to the POH specifications. The maneuvering speed decreases as the weight of the A/C decreases.
22. When landing at any high-elevation mountain airport, check the surrounding terrain while flying in the pattern and plan your future departure route. Especially look for emergency landing sites that you can use if you have an engine failure while on climb out.
23. VOR's are generally not usable in mountain flying because of high terrain and limited range. Navigation is usually by pilotage, dead reckoning, or GPS. GPS works very well and often has a terrain avoidance feature.
24. Mountain passes often have their own automated weather stations (AWOS or ASOS) similar to those at untowered airports. Pilots can get the radio frequencies for these stations from the internet or a current regional aeronautical chart.
25. Carry a survival kit, signaling equipment (such as SPOT Satellite GPS Messenger), and plenty of warm clothing, especially when flying during winter months. Carry enough food (power bars will do), water, and warm weather gear to support you for at least five days.
*DISCLAIMER: The information contained in this website is offered as an aid to the reader only. We make no representations or warranties of any kind, expressed or implied, about the completeness, accuracy, reliability, or usefulness of any of the information. Any reliance you place on the information is strictly at your own risk. Before mountain flying every pilot should understand his/her own and the aircraft performance limitations. The best preparation would also include taking instruction on mountain flying from an experienced mountain pilot or CFI
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