DFC wrote:
Therefore the simple answer is that the most efficient way to fly a jet aircraft is to climb as quickly as possible to the cruise level and stay there as long as possible.
From this you will gather that in order to stay at cruise level as long as possible requires a steep descent. Therefore the most efficient possible end to a flight would be to remain at ideal cruise level until such a point that the throttles are closed and the steepest possible path followed to landing.
The last part of this (the steep dive from cruise flight) is frankly b0llox!
Yes, aircraft get good economy at cruise flight levels, but should then descend at Vmd. The point at which you leave cruise altitude should be where a line drawn from the threshhold (allowing deceleration and running the flaps etc) intersects the cruise altitude when descending at Vmd. Remember, continuing the cruise for another 20 miles before descending balls out still uses 20 miles worth of engine power and hence fuel at cruise fuel flows vs 20 miles of idle thrust all to save about 2 minutes.