On 2008-04-24, WingFlaps wrote:
Let's work some real numbers for a 172 at 500'. Say climb was a Vx 59
knots.

Firstly, I don't know anyone who routinely climbs out at Vx - certainly
not at 500'. Secondly, this is 100 feet below the altitude I stated.
IIRC, Vy is for a C172 is in the region of 65 knots - or best glide, and
many pilots accelerate to around 70-75kts at 500 feet to get a better
view forward, since best rate in many parts of the world isn't critical
to maintain once you're above a couple of hundred feet.

pilot carries out some trouble checks say 10s. Calls on the radio =10
s and plans his return.

The sequence is aviate, navigate, communicate. Most pilots I know won't
touch the radio with a problem at low altitude. The pilot I know who did
make the turnback from 600 feet certainly didn't, he just turned back.
However, in his situation it was pretty obvious the engine had lunched
itself so there was no time spent 'debugging' the problem. (For the
record, the only engine stoppage I had on takeoff was at 50 feet - the
decision to land straight ahead was very easy and fast to make).

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!

If the pilot does that, then yes - no way. However, the pilots I've know
who've had low engine failures have never yakked on the radio, nor have
they spent 10s debugging the problem!

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.

You do NOT have to accelerate with the wind! You are a creature of the
air, turning downwind does not involve a loss of airspeed!

I agree that the primary concern is to not stall. However, pilots must
be prepared to make a decision rather than 'default straight ahead' -
the decision, whatever it is, must be made quickly and you must not
stall. And yes, sometimes, turning back to the runway is possible and
this will depend on the situation - altitude and the suitability of
terrain, pilot proficiency etc.

When you're about to push the throttle forwards, you SHOULD have some
kind of a plan if it goes pear shaped. What's the wind doing? Is there a
crosswind? What's the terrain surrounding the airfield like? If you lose
power at point X what is the best course of action, and at point Y what
is the best course of action? The best courses of action (other than 'do
not stall') may not be a fixed prescription.

--
From the sunny Isle of Man.
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