Top of Descend Mental Math

This video cover a very important topic which is figuring the top of descend (T/D) using mental math.
In my opinion as a pilot you should be able to figure out the T/D both to back up the FMC computations and be able to cope up with any sudden changes in RW or strong wind shift.

Start very conservtly and adjust and tweek the mental math as you become comfortable with the airplane.
A very good source that helped me personally understanding the desend in this airplane is a book titled "737 NG FMC User Guide" it is a must have for any B737 pilot.

T/D:
1- Altitude you need to lose, that is your cruise altitude minus field elevation. In the example in this video the cruise altitude is 12,000ft and field elevation is 600ft (consider it 1000 to make the math easy)
12,000-1000=11,000 drop the three zeros and multible by 3= 33nm.
2- Speed above 200knts. 283knts. consider the 83 knts again will assume 80 divide by 10 =8nm. ( Add this number to the miles you got from step 1).
3- Wind: each 10knts of tail wind is a mile you need to add, and for head wind subtract.
This figure is the track mile for idle power desend all the way to the RW, depending on the way you are approaching the RW you need to consider the actual miles the airplane is goig to fly. That is down wind, straight in or base.

Please let me know if you have questions or comments.

Happy flying,
Asiri