Your photograph (Flight International, 18-24 March) of the Singapore Airlines (SIA) Boeing 747 tail "cutaway" (tailscrape seems an understatement) was revealing in more ways than one.
To prevent this, most 747-400 operators use a standard take-off flap setting of 20° for all take-offs with rated/assumed temperature or derated/assumed temperature thrust as required.
Other operators, particularly in the USA, give crews a choice, which invites the possibility of taking off with flaps 10 using flaps 20 V speeds resulting in some exceedingly expensive noise in the tail area.
Flaps 20 for all operations is conservative and should prevent the possibility of tailstrikes, which would certainly negate any performance gain from using flaps 10.
As SIA is a flaps 20 operator and the landing gear oleos had to be extended for this to occur, one has to conclude that someone tried really hard.
David Connolly Brussels, Belgium
Source: Flight International
