We recently landed at Telluride Airport, Colorado (KTEX), elevation 9,100 feet. The above photo was taken at 11,000 feet inbound to land. (Note how low we are over the ridge at right, at that altitude.) The town of Telluride is barely visible deep in the valley beyond the airport. Airport density altitude was almost 12,000 feet when we landed.
Several pilot friends expressed interest in my planning process flying into such an airport, so I thought I’d share the details in a post.
First, check out the map. Telluride Airport is surrounded on three sides by 13-14000’ mountains. However it is relatively open to the west. By navigating to the Cones VOR and then turning east, it is accessible under the right conditions.
Density Altitude and Aircraft Performance
When I say accessible, my underlying concern flying a non-turbocharged airplane was not so much whether I could safely approach and land, but whether I could safely depart the 9085-foot-elevation airport in summertime temperatures. So the crux is “density altitude” (D.A.) and that’s where I’ll start.
Even before checking anything else, I knew I’d be lucky to get 65-70% of sea-level power at full throttle, and 200-300 fpm climb after takeoff from such a high elevation. So my first questions were “In the worst case could I take off in some direction without the need to climb? Better yet, could I safely descend after takeoff if I found myself unable to climb?” If I needed to climb to clear significant terrain after takeoff, I wasn’t going there.
So that crazy dropoff from the Telluride Airport westbound into the San Miguel River Valley is actually a big plus. If I could just get off the ground before the end of the runway, I’d be okay proceeding westbound even with little or no climb. I dared not take off to the east due to high terrain and little room to turn around. But visiting here was within the realm of possibility as long as I departed to the west.
Next I checked forecast temperatures for our visit. Telluride expected highs in the mid-70s and lows in the upper 40s. Those sound nice and cool until you consult density altitude charts. At 73F the density altitude would be 11,500 feet. If I departed early morning when the temperature was around 50F, D.A. would still be 10,200 feet. Wow!
Then I consulted the performance charts in my airplane’s pilot operating handbook (POH)—how much takeoff roll would I need, and did I need to clear any obstacles? I’m no test pilot and my engine is old so I all but doubled the chart values in my calcs. Even with a 1500-foot takeoff roll and some 3,000 feet to clear obstacles, the 7,000-foot runway should provide adequate takeoff margins.
Next I consulted my POH climb-performance charts. At these density altitudes my calculated climb rate was a thought-provoking 12-14 miles to clear a 1000 foot ridge in our normally peppy Skylane. (Before our first visit here several years ago, I actually climbed the airplane to 11,000 feet to confirm my climb rate under appropriate temps.) Clearly I didn’t dare climb eastward toward the mountains after takeoff, but the good news was that departing west I needn’t climb at all to clear terrain, and could in fact safely descend into the San Miguel River Canyon if necessary.
Two things I can do to shorten my takeoff roll and optimize my climb rate are:
- Take off when it’s coolest early in the morning, and
- Load the airplane as light as possible. For the latter we took minimal luggage and removed unnecessary supplies from the airplane. I also planned fuel for the 2-hour flight before taking off from Flagstaff. Although our Skylane holds 88 gallons, 45-50 would give me adequate reserve. So we took off from Flag with 75 gallons, with the target of having 45-50 departing Telluride. That put us ~475 pounds under max gross weight, not a precisely calculated target but simply based on “the lighter, the better.” If we’d had heavier people or bags I’d have departed Telluride with even less fuel and landed at nearby Cortez (which is much lower) to fuel for the flight home.
Now come weather factors. It goes without saying that I want excellent visual flight conditions before flying up a dead-end canyon. (Initial altitude for an instrument approach here is 13,000 feet, and for an airplane like ours you’d need to miss the approach some 6 miles from the runway where there’s still room to turn around. And yes, consulting approach plates is accordingly part of my planning.)
The remaining factors boil down to wind. I did not want to take off eastward over town into the dead-end canyon, nor battle downdrafts given such limited aircraft performance. Wind flows over mountains like water over rocks in a brook, so I dared not accept significant winds from north, east, or south due to potentially severe turbulence and downdrafts tumbling over the high surrounding mountains. Anything stronger than light westerly winds would also generate turbulence and force me to land downwind. There’s hardly room to circle-to-land nor on climbout, so I decided I wouldn’t accept any wind beyond a few knots from the west.
This is a relatively busy non-towered airport in a narrow canyon with effectively a one-way runway (land east, depart west). Many visitors arrive in jets. If there’s much traffic when we arrive or depart it’s best to to avoid conflicts by lingering outside the canyon or on the ground until things quiet down.
Consult with Local Pilots
Based on this assessment the flight sounded quite doable. I always phone ahead to unfamiliar mountain airports for guidance from a local pilot. So to reinforce my conclusions I phoned Telluride Airport to ask whether many light aircraft come in at this time of year and they said yes. But those answering were not pilots so I phoned area flight schools hoping a local pilot with Telluride experience could give me a summertime operations report. Finally I reached someone at Cortez Airport who said they do see quite a few light aircraft coming or going from Telluride. In a telling example he told of a Comanche pilot who came in the day before and checked extra luggage with him for the weekend to lighten the airplane before flying in and out of Telluride. (That pilot sounds like a wise one!)
Noise Abatement Procedures
Even then I was a little nervous, but logic and homework said we’d be safe. My final planning step was investigating and refamiliarizing myself with Telluride Airport’s noise-abatement procedures. (Check for these on any given airport’s web page, as they’re not always available through normal flight-planning channels.) By following noise abatement procedures we help keep our favorite airports open.
It’s all about Airspeed
Okay, now let’s talk about the actual flying, much of which boils down to speed. As you know, we fly all our pattern work and approaches at “indicated airspeed” read off the airspeed indicator. That remains true whether you’re operating at sea-level Nantucket or Telluride.
ALWAYS FLY THE SAME INDICATED AIRSPEEDS FOR AIRPORT OPERATIONS REGARDLESS OF ELEVATION. If you approach sea-level Nantucket at 60 knots indicated, you should also approach Telluride at 60 knots indicated.
That being said, it’s true airspeed, not indicated airspeed that in no-wind situations defines our speed over the ground. This of course is why when cruising at altitude your airspeed indicator might show 100 knots when your true airspeed and hence groundspeed might be say 130. True airspeed increases by about 2% per thousand feet, so at Telluride you’re truing about 20% faster than at sea level. Why does that matter?
- The plane feels like it’s going much faster than you’re used to on final approach at sea level, so pilots sometimes make the dangerous mistake of slowing below normal approach speed because “this doesn’t feel right.” Obviously you’re going to touch down faster, too.
- You may have wondered why landing distances increase with altitude like takeoff distances do. The reason is because you’re going faster over the ground at the same indicated airspeed so consult your performance charts for adequate runway length.
- Since you’re flying faster, the airplane’s turning radius increases, just as it does when driving faster in a car. You may be familiar with accidents where airplanes flew up a blind canyon and lacked room to turn around. Larger turning radius at the same indicated airspeed is one reason why. This is one reason why pilots generally avoid circling to land or taking off east at Telluride–you need more room to turn around. If you must reverse course in a tight canyon, maneuver the plane to one side, slow down, and drop a notch of flaps to reduce turning radius.
High Density-Altitude Takeoff Procedures
Finally, a few general tips regarding high density-altitude takeoffs.
- As mentioned, clearing obstacles or terrain after takeoff is a major consideration as to whether you can safely depart a given high-elevation airport. Along with studying the charts beforehand, when arriving at a new-to-me high-elevation airport, I scout the terrain from the traffic pattern BEFORE LANDING and note what direction I could fly after takeoff toward the lowest terrain with minimum climb. I then record that info and clip it to the yoke. Departing Telluride the only way to go is west down the San Miguel River Canyon. Here at Flagstaff, the terrain descends toward the south over I-17, but departing in any other direction requires climbing. If takeoff performance stinks, I want to know before takeoff which way to steer.
- Lean the engine at full power during pre-takeoff run-up to ensure maximum takeoff power. This is done the same way as you would in cruise, with a nudge toward the rich side of peak rpm or EGT.
- Following rotation, accelerate in ground effect to best rate of climb speed before beginning your actual climb. Since engine power and propellor efficiency are diminished at high density altitude you will not experience the sort of acceleration, clean rotation, and climb performance you’re used to. This procedure prevents you from pitching up too much/too early into climb and potentially stalling the airplane upon leaving ground effect.
- Among the biggest threats of high D.A. takeoffs and landings is perceptual. Prepare yourself mentally to fly by the numbers, regardless of what you see out the windshield. You’re gonna feel too fast approaching to land, and be startled at the long runway roll and poor climb rate on takeoff. (Expect to clear obstacles by dozens of feet, not hundreds as you might be used to.)
We Made It!
Jean and I launched for Telluride Friday morning, and with tailwinds flew a smooth and uneventful 1:45 flight. We spotted the airport shortly after entering the canyon, and with no other traffic, landed uneventfully.
Following a fun weekend of hiking and dining we roused our hosts too-early Sunday morning to take us to the airport, and although our takeoff run was long we cleared the runway in plenty of time. Density altitude at 8am, with outside air temp ~50F, was 10,200 feet. Our climb rate ranged from 3-500 rpm, not impressive but better than I’d expected. That marginal performance actually turned out to be a plus because as we rolled down Runway 27 a jet reported inbound on the Runway 9 instrument approach but we passed way below him still climbing out of the canyon. (Another good reason to have previewed instrument-approach paths and altitudes, so we knew we wouldn’t conflict.)
You’re probably thinking “that’s a crazy amount of work and planning just to land somewhere.” That may be true, but our lives could depend on it. And once you’ve experienced a given airport a time or two the process is much simplified. Now that I have twice personally experienced Telluride’s setting and terrain, and know that the Flying Carpet will take off comfortably from there at a given weight and density altitude, I’ll need to do little more next time than check weather parameters–and be prepared to cancel or stay over if those parameters depart my safety range.
This is not intended to provide comprehensive guidance as there are many more mountain flying principles not described here. But hopefully you’ll find this example useful for basic understanding.
PS: Those flying turbocharged aircraft will experience all the above effects but with better takeoff and climb performance. (You’ll still use more runway on take off and landing.)
©2019 Gregory N. Brown