During my last trip to Sandakan, I managed to capture the pictures above on my afternoon flight back to Kota Kinabalu. The day before I also took the afternoon flight but sadly took the window seat of the wrong side of the aircraft. Anyway, on the flight back, when I checked-in early and asked for the seat which gets the best view of the Mountain. Thank you to the nice lady at the counter, now I know its seat 8F or 9F for the Boeing 737 flight between Kota Kinabalu and Sandakan. Never take 7F because it has no windows to speak of.
Now that you know, reserve the seat when you buy the ticket or do an early check-in through the web or by arriving early at the airport. Another thing is I suppose it's also be best if you could take the early morning flight (as of now, around 730am from Kota Kinabalu) rather than the afternoon flight. You can see that there's a lot of cloud surrounding the mountain. Have a good view.