I got a nerve-racking but painless lesson in density altitude a couple of
years ago in sounthern France. I'd flown my girlfriend and I in a
Taylorcraft BC-12D from the UK to Chateau Chassagne near Dijon. The
temperature in the UK rarely gets much above about 80 or 85 even in the
summer, but the performance of the airplane is noticably different than in
the winter.

While at the chateau, the temperature got up to about 100. I offered to
take the chef up for a ride in the Tcraft. He was a big lad. I taxied out
to the end of the grass strip (surrounded on the right and departure end by
trees, naturally), turned into nearly zero wind, and firewalled the
throttle. As the grass went by and went by and kept going by, every bit of
my knowledge of density altitude shot through my mind in a serious "Oh,
Sh*t, I hadn't thought about this!" moment. We finally broke ground way too
far down the runway and she wasn't climbing like she should have. I kept
the nose up as high as I dared, pleading it to just clear the trees - that
was all I wanted; just to clear the trees and we could sort everything else
out after that. The trees kept coming, the plane kept not climbing, and it
was looking pretty dire there for a few moments.

Well, we finally reached the tree line and cleared it by a mere few feet.
No harm done in the end and my passenger didn't know enough to know just how
close it had been. But I was sweating bullets for the next 20 minutes and
it had nothing to do with the heat.

Lesson there - when you're not flying in your normal environment, take a
moment to think about all those things you take for granted on your home
turf! Density altitude DOES matter, you just might not need to think much
about it where you fly.

Cheers,
Shawn



"Corky Scott" wrote in message
...
On Wed, 13 Apr 2005 19:54:29 GMT, "Jay Honeck"
wrote:

It would be child's play to make a chart that says "when the temperature
is
'x' and the altitude is 'y' your runway must be 'z' length" for each
aircraft type. In fact, I'm surprised that this isn't a required part of
the POH.

There in fact IS such a chart. It's actually one of those adjustable
cardboard devices that allows you to dial in various parameters such
as temperature, altitude, wind, direction of wind, runway surface
type, whether it's sloped up or down and by how much, what type of
airplane etc. etc.

Dial all that stuff in and the calculator reads out the necessary
runway length. Compare that to the runway you are about to use.

I found mine at Sporty's Pilot Shop. Saw it recommended in the "Hold
on Harvey (or whatever the name was) FAA video about density altitude.

There were three very sobering video's in the VCR. The above
mentioned one was poor quality because the Video cam wasn't found for
several years or so in the wreck. It was shot from a Cessna L-19, or
the civilian version of it and there were two guys in it flying up a
mountain range that kept getting higher and higher. They got
themselves trapped heading into a mountain canyon that rose faster
than they could climb and attempted to turn around. The pilots last
words were "Hang on Harvey (or whatever the passengers name was)" and
you see the ground go upside down. You can hear the stall warning
horn going off as the pilot attempts the turn (to the right). He
drops the nose, but then has to pull it back up right away because the
ground is so close. The stall warning horn goes off again and the
ground goes upside down.

In the second accident you are looking at a scene in a really rugged
canyon from the hikers viewpoint. They hear the sound of an airplane
and a Cessna goes by at about their eye level. You hear them
discussing it and then the airplane noises come back and you see the
airplane coming back at them, but below the rim of the canyon. It
smashes right into it below them.

The third accident was the best quality video because it was shot at
an airshow. It looked like it was a Beech T-34 or something very
similar. It was at a high altitude runway and it was apparently very
hot. The pilot goes up for a loop and as he's rounding out for the
pull out, he runs out of air.

All of these accidents were due to the pilots not understanding the
affect of density altitude on the performance of their airplane, and
not allowing for it.

In addition to the crash video's there is a comprehensive discussion
by a very heavy set FAA crash investigator who had an ego to match.
He was impressively overbearing and caustic.

Most density altitude misshaps occur in the high plains or mountain
area's of the west, but not all of them.

There was a density altitude related accident here at a local turf
runway airport in Vermont a number of years ago. A pilot (think he
was flying a Cherokee) was visiting and decided to take off with three
passengers during the heat of the day (it was high summer). Several
of the local pilots got in his face and aggressively spoke to him
about the situation pointing out how hot it was and that with the full
load what effect that would have on his marginal performance and tried
to persuade him to wait.

He relented and waited another couple of hours then decided he was
going to go and loaded his passengers, one of whom was his son. Again
the pilots intervened. One offered to drive the passengers to the
nearby Class D airport (KLEB) which has mile long paved runways. He
could fly there, pick up the passengers and take off with his full
load no problem. He refused the offer.

His takeoff was to the north, which is slightly uphill. The airplane
broke ground abouth 3/4 the length of the 2500 foot long runway and
wallowed nose high along the runway without gaining much height.

He wandered off to the right in this condition with his nose so high
he probably could not see the tall pinetree he flew into that bordered
the runway.

The airplane clipped off the top of the tree and crashed nose down on
the far side of it killing the two front seat occupants. His son and
the other rear passenger survived.

Corky Scott