As this is GA forum, if we consider very much average types such as Cessna 150/PA-28 they will descend in a glide at about 750 ft per minute on thereabouts (going from memory a bit ) if flown at best glide speed. Surely, in excess of a minute is sufficient time to execute a 180 degree change a heading – in a Cub I can do that in well under 10 seconds, probably 5-6 if really well-motivated.
I think this is the assumption that a lot of pilots make and it ends up getting them in trouble (stall/spin accidents). In order to maintain a given IAS through a turn you must actually lower the nose which in turn increases your decent rate (this is in an engine-out situation). You can assume that such pilots who don’t survive their turn back to the runway steepened their bank to expedite the turn back to the safety of the runway BUT also kept the nose at the pitch attitude for Best Glide speed in straight-level flight. You can understand one’s apprehension to lower the nose and increase their decent rate when attempting to glide back to the airport but without doing so they encounter an accelerated stall and suffer the resulting spin.
The quicker/tighter you plan on making that 180 degree turn back to the runway the more you have to lower the nose and suffer the resulting increase in decent rate. Remember, as your bank angle increases your Lift Vector decreases. Some of this is masked under normal situations where you have power available unlike in such emergency situations.
You are correct when looking at the situation as measured by time left resulting from your decent rate at Best Glide. But as soon as you begin manuveuring with turns that time aloft becomes greatly shortened. For that reason the often mentioned procedure is to establish your Best Glide speed and continue forward. Doing so gives you the most time to prepare for the eventual landing.
Now I’m not saying that turning back towards the runway isn’t an option but it has a lot of unknown variables that you don’t have time to weigh in such emergencies.
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