I fly the 737 NG series.
Recently my captain showed me something which completely foxed me and forced me to come here and share my qaundry with you folks.
My captains theory was that taking the same set of conditions for two aircraft, a heavier one will start its descent earlier!!
We checked this on the FMC and a difference of 10 tonnes to the ZFW on the Perf init caused to ToD to shift approximately 30 miles out!!!
Could somebody please explain how this works!
Regards,
A