ENROUTE DESCENT PLANNING
Goal: Reduce time to destination by descending at an IAS that is higher than the max range airspeed.
This type of descent is used when saving fuel is less important than time to destination.
Procedure: To calculate VSI, divide altitude to lose by nm to go times groundspeed. For example,
cruising at FL 300 and center clears you to descend and maintain 15,000 ft in the next 50 miles.
Substituting these numbers into our equation: (-15,000 ft/50 nm) (5 nm/min) equals -1,500 ft per min. Of
course, the specific VSI depends on groundspeed, but the following table provides a rough approximation.
From cruise power and IAS at altitude, lower the nose to accelerate (if necessary) to desired descent
airspeed (usually 250 KIAS), then reduce power (if necessary) to maintain desired VSI. At altitude, you
will need to reduce fuel flow by approximately 50 pph for every -100 ft of VSI. Remember you must
request permission to perform directed descents at rates less than 500 fpm.
Max Range Descent
Goal: Use less fuel while maximizing distance traveled. NATOPS lists the max range descent airspeed
and descent point in the BINGO tables for various airspeeds and configurations. Max range descent AOA
will be higher than the max range cruise AOA (triangle at 12-13 units). Center normally plans to descend
you at your altitude plus ten, so you may need to ask for an earlier descent. For example, the let down
point for max range descent from FL 350 is approximately 123 nm but Center would not normally descend
you until 45 nm. A rough approximation is to let down three and half times altitude plus desired DME from
field level off.
Goal: Minimize downrange travel if your descent is delayed by ATC or weather. Use this strategy when
you are forced to stay higher than desired. At altitude, maintain max endurance AOA (box at 14 units)
until cleared lower, then lower the nose and accelerate to 250 KIAS, reduce power to idle and use boards
as necessary. The idle-with-boards configuration gives the maximum altitude loss for distance over the
When descending through 5,000 ft AGL, call platform and comply with the minute to live rule. When
practical, retract the speed brakes.
Descent Comparison, no wind, 2,000 # FUEL: T-45A (all figures are approximate)
FUEL FLOW (pph)
DME TO LOSE 1 K
500 (idle), BDS