On Apr 25, 3:12*am, Dylan Smith wrote:
On 2008-04-24, Brian wrote:

Depends on what you mean by "the impossible turn". If you mean turning back
at 200 AGL, yeah, that one's pretty much impossible. If you mean 600 AGL,
it's pretty much possible in the average aircraft. (Hell, that's pattern
altitude at EFD!) The line lies somewhere in between.

It is statements like this that get pilots killed.

It's statements like 'never turn, always land straight ahead' that also
gets pilots killed. There are plenty of airfields where going straight
ahead is quite possibly the worst option, and the best survivability
options are at least a 120 degree turn away from whatever point you're
at when at 600' AGL.

The only thing you can do is use the best judgement at the time. You get
one chance - it may be wrong. Sometimes, trying to turn back might be
wrong. Sometimes doing anything *other* than trying to turn back might
be wrong.

In gliders, every glider pilot is taught "the impossible turnback" from
200 feet (which, in the typical low performance training glider, is
about equal to turning back at 600 feet in a C172).

It's the L/D that makes it much harder in a typical powered plane.
This means that all manouvers lose energy much faster. The turn back
needs at least 2 turns as well as acceleration if there is any wind.
You will note that nearly all the accidents are stall spins -a moments
thought about the situation will make you realize why this is. The
turns are made tight because there is not enough height/time for a
lazy turn.

Let's work some real numbers for a 172 at 500'. Say climb was a Vx 59
knots. The plane must first be accelerated to 65 for best glide. The
pilot carries out some trouble checks say 10s. Calls on the radio =10
s and plans his return. Note that 20s have probably elapsed. The plane
has already travelled ~0.4 miles and at a 10:1 glide ratio has lost
200' (assuming he did get it to best glide in the first place). Can
he make 2 turns and land back -no way!

Ah you say, I'm a much better pilot, I would loose not more than 10
seconds in starting my turn back., trimming etc.
But how much does the turn back cost? Assuming you keep to 45 degrees
of bank to stay _above_ stall (the stall is now damn close -better
hope there's no significant wind) the turns are still going to cost
you 35 seconds. 45 seconds lost = 450 feet! Now we add in the energy
losses from having to accelerate with the wind and to glide speed.
It's still an impossible turn. Try to tighten that turn more and you
have to dive to accelerate to avoid the stall and what does that do to
your energy management and turn radius?

Now what safety margin is appropriate for you and you PAX? Say 100%
in that case, unless you've climbed to 1000' don't even think about
turning back but practice spotting good landing sites.

I've also heard a lot of BS in this thread about not having good
palces to put the plane. There is nearly always somewhere flat to put
the plane within 90 degrees of the runway centerline -even a road.
Malls have big parking lots! Put it down flat in landing config and
you will probably survive, stall spin and you'll DIE along with your
PAX. A good pilot looks at the airport environs in a strange airport
and may ask about options at the runway end for this emergency.

Cheers