FergWorld : Articles : Mountain Flying
By Ryan Ferguson
(cont'd from page 2)
Leaning Technique
CPA-recommonded method
- Normal run-up.
- Taxi into position and hold.
- Apply brakes.
- Full power.
- Lean for 50-100 degrees rich of peak.
- Release brakes.
Alternate method
- Normal run-up.
- At highest normal run-up power, lean to 200+ degrees rich of peak.
- Taxi into position and hold.
- Full power.
- Release brakes.
- Tweak mixtures on the roll.
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Departing at a high density altitude means you'll need to pre-lean the fuel/air mixture to the proper setting. There are as many ways to lean as there are pilots. The CPA advocates a full-power runup to determine the appropriate lean peak and resultant 50-100 degree Rich of Peak power setting. An alternative that I selected was to tweak the mixture on the roll after doing a normal runup and setting the mixture approximately 200 degrees rich of peak at 2000 RPM. For my particular aircraft, this gave me a conservative power setting which didn't burn up my engine and only required a slight tweak on the roll to get right on target. This isn't for everyone; your mileage may vary.
A sure sign of a flatlander's arrival at a mountain airport is the flare and rollout, followed by sputtering and then silence from the engine compartment. What happened? You guessed it - the pilot ran through his normal GUMPS checklist and enrichened the mixture to the full rich setting prior to landing. Once ground-laden, the engine had no choice but to give up as it was flooded with an overly rich fuel-air mixture.
Depending on your altitude, cruise power at high elevation is likely to also be maximum power. If this is the case, your fuel-air mixture is already properly set and requires no adjustment for landing.
Back to the cockpit
Mark Stevenson, my instructor for the flight portion of the course, sells Cessna Citations for a living. He must do this for the sheer enjoyment of it; he seems to be having as much fun as I am. He's successfully imparted a small portion of his knowledge onto me; I can now visualize the westerly wind flowing like water over the peaks as we depart Boulder Municipal airport (1V5) heading west. We're flying 'upstream,' and as we head toward the Front Range, I know we'll fight a downdraft pouring over the ridge, to be followed by an updraft as we pass clear of the mountain.
"I feel a bit uncomfortable charging towards the terrain, but I soon realize we are already well clear of the ridge. Optical illusion #1: the horizon is not the ridgeline. The horizon is well below the ridgeline."
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There's a mountain pass in this picture. Click above to see it outlined with my digital red pen. |
I don't know what a mountain pass looks like. There are tall mountains in front of me, running north to south as far as the eye can see. "Where's the pass?" I ask him. Mark points out what looks like a flat spot on the Front Range. I see it; I don't see terrain beyond it. "Will we need to circle to gain altitude in time?" I ask.
I'm still new at this. Mark says no; we're getting 400 feet per minute with three souls aboard and fully fueled main tanks. Our auxiliary fuel tanks are empty and my petite wife is sitting in the back seat enjoying the view. We'll gain altitude with time to spare before we come close to the pass. I feel a bit uncomfortable charging towards the terrain, but I soon realize we are already well clear of the ridge. Optical illusion #1: the horizon is not the ridgeline. The horizon is well below the ridgeline. It would be easy to fly around all day in a nose high attitude, not understanding the visual cues of the terrain.
The CPA recommends passing the ridge at a forty-five degree angle, at least 1,000 feet above the terrain. As soon as the ridge is 'made,' the pilot turns the remaining forty five degrees to depart the ridge at a ninety degree angle.
The reason? The pilot must always be ready to turn towards lower terrain if the fan(s) stop spinning. If one loses the engine just before crossing the ridge, he/she can turn ninety degrees, right back towards lower terrain, versus a much less feasible 180.
"I'm pleased as we easily clear the ridge. 'You were right,' Mark nods, and gives me back my engines. Yes, Mark made his point: plan every ridge crossing as though an engine failure was imminent. "
"Let's challenge each other to look for good landing spots the entire time we're flying," Mark says. I have two engines, but I'm nearly at my single engine service ceiling just sitting on the ground at Boulder. Losing one out here is better than losing two, but such an event merely gives you more time to plan your emergency landing. "Tell me when we have this ridge made," Mark tells me.
Okay, fair enough; I angle in to the pass, fight a slight downdraft, and watch the ridge pass below me. "We're clear," I say, and start turning directly away from from the cumulogranite. "Let's see if you're right!" Mark exclaims with glee, and closes both of my throttles to idle.
It so happens I have an aftermarket FAA-approved POH for my Twin Comanche, and it includes a best glide speed, normally not published for many light twins. I know that for maximum gross weight, Vg is approximately 110mph; considering the altitude and slightly lightweight configuration my aircraft is currently in, I shave off a few mph and pitch for 105. This is good, because the ship rapidly loses altitude, and I want all the altitude I can keep. I'm pleased as we easily clear the ridge. "You were right," Mark nods, and gives me back my engines. Yes, Mark made his point: plan every ridge crossing as though an engine failure was imminent. It's a phase of flight that is nearly as critical as takeoff. Next: The route.
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