The most efficient way to fly is to maintain cruise as long as possible to give you an idle power descent. Any power used during the descent is inefficient as that fuel would have been better used in the cruise. A 3 degree descent from cruise is not good to aim for- it does not allow for strong wind components and in a strong headwind will result in a premature descent and power all the way down to maintain a 3 degree profile. Similarly, a strong tailwind would get you high on a 3 degree profile causing extra drag needed, showing you cruised too long and wasted fuel. Remember, any power application, use of speedbrakes or large speed adjustments during descent shows you have misjudged and cost yourself fuel (barring external causes like ATC, STARS etc. You should not think in terms of 3 degree descents until on final approach.
Pressurisation systems are designed to cope with an idle power descent from maximum pressurisation altitude quite happily.
Any wild RODs of 3-5000fpm are due to very coarse FMS control and should not be accepted. FLCH on the 747 gives idle power/maintain speed sometimes better than VNAV control. You should never get more than 2500fpm. Until you are quite experienced, 250 kts below 10,000' is advised.
Last edited by Notso Fantastic; 7th Jan 2005 at 13:28.