The idea of 20 mins is IMHO a management and commercial motivation and control tool used on the crews.
If the aicraft cruises at 3oo kts and the distance is 300nm then the timetable time is one hour and if you also give the staff 20 mins turnaround then most crews will try to achieve both. They are unlikly to achieve this and will modify proceedurs in their attempts and thus achieve OVERALL time improvements and importantly at their own risk.
These unreal schedules will promote a feeling of failure and inadequacey among the crews and a feeling of not achieving and ensure that most crews strive harder.
They will also be used in pay negotiations to show under achivement by crews.
These schedules generate stress and then incidents and to management of most airlines this is ok as long as their personel hands are clean, the Caa does nothing positive to stop it, and the insurance companies remain blissfully unaware and inactive.
This was a managers explanation in 1973 regarding the HS 748 multi leg around the uk day/night, and please keep one engine running all the time on the turnround, taxi in out on one etc etc. As a fo I thought it was mad and resigned.
Ps What was the result of all that effort? Treat you good did they?
These management ideas are like thermo nuclear war to airmanship and safety, the only way to win is not to play.
I expect this is all a similar tool/scene to the min fuel one.
Some adrenalin addicts will go for anything the managers dangle in front of them.
Still its your licence and it was easy to get was it not?
Remember the Faa/Caa exists to take it away if you mess up and this part of their job they will do.
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We will do the drill according to the amendments to the amendments I er think?