Back on the subject of flap selection- is there a benefit? Some interesting points come up...
Originally Posted by Wornout Rubber
What is interesting to note is the difference of only 5 kts between Vref 20 and Vref 25. Also at Flap 20, there is a substantial reduction in drag and hence thrust required. ( N1 thrust 40.2% for F20 as opposed to 50.7% for F25).
Two good points. First is, Vref increases 1kt for each 1 deg of landing flap 'you dont have' which is a rule of thumb in some older jets and turboprops.
Second, the big difference in thrust required to 'balance' the drag in a transport category aircraft when flaps are set to landing range. Quite different to the wing we were flying when we were doing PFLs in our
ab initio. Again it is through the mists of time, but during our type ratings we all would have seen the very high sink rates and huge amount of thrust required to recover from a stall or incipient stall in the landing configuration, throttles closed.
Another general characteristic of flaps on transports can be found by going back to another rule of thumb from an earlier generation: flap for circling. Take a look at your FCOM or company training manual and note the recommended flap (and speed) for a circling approach, or bad weather circuit. It also probably corresponds to the max flap for T/O setting. That would be the flap setting at which, very roughly, proportionally 'more lift added than drag.'
But its all academic. If you experienced a repeat of this situation, selecting a lower flap setting would not help you, even if it was a 'better' glide range flap, whatever that might be. For you would be in the same predicament as after a decreasing performance windshear event - you would be too slow to take advantage of the 'better' glide flap. You would first need to push the nose down to accelerate. And in a 50 tonne or 250 tonne transport, that is a massive change of momentum, that is going to use up a lot of altitude, of which you have precious little.
Originally Posted by galaxy flyer
fly the plane and take the short landing UNDER CONTROL
Dead right. Lose all thrust in that situation, not even Bob Hoover will make the runway. Forget the runway. Fly it to the ground under control.