DC-9
The company book says climb and descend at 280kts and long range cruise .73-.76M (We don't got no fancy 'box' in them there planes.)
Most guys go up and down at 300-330 and cruise at .78-80Mach and will under-burn the computer by 500-1000lbs per leg.
CLIMB: Sometimes aero equations are no match for pilot experience. L/Dmax is approx. Weight + 100 = kts. So this implies slower is more efficient, but I say BS. At the 10,000' acceleration it only takes another minute climbing at 1000fpm to go from 280 to 320 kts. Fuel flow will be the same b/c you're at climb power. The difference comes in at the glass wall that starts between 17,000 and FL220. {This is especially true on -7 or -11 engines and is even worse on a hot day.} The climb rate will be 200-400 fpm higher at 320 versus 280 and you have been going faster during the whole climb at the same burn rate. Inertia.
DESCEND: At first glance it makes sense to go to flight idle nice and early and stroll down at 280 kts. OR you could stay at altitude for an extra 2-3 minutes and descend at 300-330 (or clacker) to 25-30nm from the field. It only cost you another 2 minutes at cruise but again you are going faster so you will be in the air less time (ie less burn). If you fly the book profile and are off or get a short vector, you are now burning a lot of gas down low. Having the extra smash buys a little more time for deviations. And even if you tend to be a little high and have dirty up at little earlier than optimum. On average you will save gas because you are spooling up the motors at 1000AGL rather than 30 miles ago.
Take all this with a grain of salt because:
1. The DC-9 can get down in a hurry if you need it to
2. I fly boxes so customer comfort is not a factor
3. I fly at night so Center is less likely to say lose 12000ft in 3 minutes, maintain 250 kts.
4. I have a type A personality and get too many speeding tickets
The company book says climb and descend at 280kts and long range cruise .73-.76M (We don't got no fancy 'box' in them there planes.)
Most guys go up and down at 300-330 and cruise at .78-80Mach and will under-burn the computer by 500-1000lbs per leg.
CLIMB: Sometimes aero equations are no match for pilot experience. L/Dmax is approx. Weight + 100 = kts. So this implies slower is more efficient, but I say BS. At the 10,000' acceleration it only takes another minute climbing at 1000fpm to go from 280 to 320 kts. Fuel flow will be the same b/c you're at climb power. The difference comes in at the glass wall that starts between 17,000 and FL220. {This is especially true on -7 or -11 engines and is even worse on a hot day.} The climb rate will be 200-400 fpm higher at 320 versus 280 and you have been going faster during the whole climb at the same burn rate. Inertia.
DESCEND: At first glance it makes sense to go to flight idle nice and early and stroll down at 280 kts. OR you could stay at altitude for an extra 2-3 minutes and descend at 300-330 (or clacker) to 25-30nm from the field. It only cost you another 2 minutes at cruise but again you are going faster so you will be in the air less time (ie less burn). If you fly the book profile and are off or get a short vector, you are now burning a lot of gas down low. Having the extra smash buys a little more time for deviations. And even if you tend to be a little high and have dirty up at little earlier than optimum. On average you will save gas because you are spooling up the motors at 1000AGL rather than 30 miles ago.
Take all this with a grain of salt because:
1. The DC-9 can get down in a hurry if you need it to
2. I fly boxes so customer comfort is not a factor
3. I fly at night so Center is less likely to say lose 12000ft in 3 minutes, maintain 250 kts.
4. I have a type A personality and get too many speeding tickets
