I've been spotting this morning at the 25L (refugee center 127bis). Weather was poor and rainy
Anyway I noticed that 25L is now more and more used for take-off. Is there a specific reason ? It was the case for one DL 767, one AA 767, one of the two Birdy/SNBA 333 and the BG D10 in not even 1h 1/2 time window.
Now I've seen that many of them had to wait for quite long at the holding point of the taxiway leading to the 25L. The SN 333 burned quite a lot of fuel in this exercise... and then off course they have to do a 360° to line up. So IMO not the easiest/most logical procedure.
The reason is simple:
25R isn't available over the whole length (yet), there's only 2500m useable (I think). I think ATC let pilots chooses what they want for TO.
I also saw some other heavies taking off from rwy 25R, such as Saudi MD11-F and Korean B744F.
The problem with using 25L for take-off is that there is no taxiway to the beginning of the runway. The a/c have to taxi down the runway (this is called backtracking) in order to reach the threshold. If it is an active runway it means the departing a/c have to wait.
The maximum t/o weight to use a certain runway depends on several factors : wind (speed and direction), qnh, temperature, and status (wet, dry, snow, .....).
This is why these days you can see some heavies using 25R from intersection B3 (2780m) and others use 25L
This morning (first day of school) a SNBA A330 and an AA B763 crossed our school very low after take-off on runway 25L. Really spectacular to see it suddenly appear in front of the window !
Is there any explnanation to this ? 
