The Sierra Nevadas / G. Thomas, Wikipedia
I am a Florida boy who learned to fly at mean sea level. As such, I do not care for a couple of things. The first is cold, the second is high density altitude.
Many pilots do not understand the concept of density altitude (DA). When the temperature is high, particularly at higher pressure altitudes, the DA is increased. When DA increases, there is less air for the airplane and the engine to work in flying. In other words, you lose a lot of performance capability.
Inexperienced pilots do not know what this means when it comes to taking off or landing and sometimes they completely underestimate what high DA does to their climb capability. This is across the board, for all airplanes.
For instance, when I was a younger pilot flying A-7s, my first encounter with high DA took place at NAS Fallon, NV. I was thankful for a thorough brief by the more experienced pilots of the squadron, which prepared us new guys for the first landing at an elevation of 3,934 feet MSL on a hot day. I will never forget how much more energy there was on the jet at touch down—all with normal parameters; I can remember sitting in the cockpit muttering, “Whoa, Big Fella!” as the Corsair blew past the nine board on a 14,000 foot long runway, still with great speed.
That experience did not hold a candle to taking off in my Cessna 170 later on at Truckee Tahoe.
I was flying around with a couple of other Navy officers. We went over to TRK for an airshow. When we were on downwind, a pilot flying a Mig 15 for the show treated us to a long and hot landing. The result of course, was running off the end of the runway. Luckily, no one was hurt and there was little damage to the Mig.
The show was great and it was time to leave. I figured take off gross weight was somewhere in the range of about 2140 pounds, about 60 pounds shy of gross weight. I looked at the performance charts and calculated all I needed to know. And what I needed to know was a bit discomforting.
Takeoff distance was incredibly long and the initial climb rate was less than 200 fpm. When it was out time to go, I pulled onto the runway, ran up the engine to full power, and started leaning. I tweaked the mixture control until I had the highest rpm out of the engine and released the brakes.
Now, down here in normal life at MSL, the airplane typically lurches down the runway. Up at TRK with a DA of about 9000 feet, she just sat there. I could almost hear her turning around and asking, “Really?”
Then she protested and started rolling forward ever so slowly. I felt as though I had enough time to read the latest Trade-A-Plane before reaching rotation. Finally, there was enough ‘q’ on the aircraft to get the tail off the ground and eventually, we had enough to liftoff.
The climb rate was in fact, measly. The VSI needle settled on the face of the instrument slightly less than 200 fpm. Fortunately, takeoff was off to the north into somewhat initially flat terrain.
Yeah, I am a Florida boy who likes the lower DA of MSL. But I also really liked the scenery of the mountains. If you ever have the chance to fly out west in the Sierra Nevadas, the Rockies, or elsewhere, take it. The flying is spectacular.
Just be careful and study your performance charts.
-30-
© 2011 J. Clark
Joe:
For my job, we routinely operate out of high altitude strips. The airfield I was based at in Mexico was at an altitude of 8,500 feet. One of the mountain strips in Peru was at 9,000 feet, with a shear drop (cliff) at the end of the runaway (if you weren’t flying by the end of the runway, you were going to be) The airfield in Afghanistan was at 6,500 feet. But, the highest strip I ever flew into was in Bolivia, at 13,000 feet. Performance planning, to make the climb gradients is an absolute must.
Mike,
I have always wanted to takeoff from a runway too short for the 170, with a shear, as you describe. That would be so great! And I know what you mean about those climb gradients…
jC
Performance on airplanes is about the only thing I like about Minnesota winters. They practically jump into the air. No so much in the hot humid summer months of July & August.
Jeanne,
I have had some of my students who came from Minnesota, Wisconsin, and the Dakotas reflect on the same thing. It used to get cold in the California desert when I was out there and I have to admit, I do like the climb performance when it is cold… I just don’t like the cold. ;o)
Joe
The sea level elevation and temperate climate of Bankstown in Sydney, where I fly out of, has not presented any serious performance issues for me (as yet). Though when I started my training in early March, we still had some 30 degree plus days and climb performance on the Warriors I’m flying was woeful.
I’m very mindful of this issue, however. Coming to the middle stages of my cross-country navigation flights, I’m starting to fly into airports of elevations around 3000 to 5000 feet, and while this is negligible compared to elevations elsewhere in the world, it does have a notable impact on performance, especially as we’re now headed into winter.
Clarifying my earlier comment: of course, this winter I’m going to get BETTER climb performance at high altitude. When I’m flying out there during the Australian summer it will, of course, be a different story.
I assume you meant “30 degrees C” in your first comment? The difference between C and F should be kept in mind – 30 C is a nice day while 30 F is freezing.
Joe, I like the way you include climb performance in DA computations. Runway length seems to be everyone’s focus and sometimes getting off the ground is the least of the problem.
Indeed, doesn’t do you any good to get it off the ground, only to fly into the side of the hill a couple of miles away just because your plane was incapable of climbing out well enough.