Flight Descent Planning
Also known as Vertical Navigation , flight descent planning allows you to determine when to start a descent , or what rate-ofdescent to use , so you can also use flight descent planning procedures to monitor and back up ATC altitude guidance and control , and to confidently comply with complex altitude clearances .
Climb Planning
The procedures on this page are also applicable for climb planning ( i . e ., when to initiate a climb in response to an ATC crossing altitude restriction clearance ) – just change Descent / Descend to Climb , and change Altitude to be Lost to Altitude to be Gained .
Calculating the Distance Required for Descent
The general formula used for calculating the distance required for descent is ‘ 3 times the height ’, where the ‘ height ’ used is in multiples of thousands of feet . A more accurate figure is obtained using : ( 3 x height ) + ( 1nm per 10kts of speed loss ) + ( 1nm per 10kts of Tailwind Component ) The ‘ speed loss ’ in the above formula is the difference between the maximum speed used during the descent and the minimum zero flap speed . For an average case of a maximum speed used during the descent of 300 knots and a minimum zero flap speed of 210 knots , this would therefore give a correction of 9 nm . Add to this occasions where a tailwind of 50 knots – 100 knots exists during the descent and it can be seen that corrections in the region of 15 nm – 20 nm may be required in order to give an accurate distance calculation rather than the general use of the ‘ 3 times the height ’ rule . Even without a tailwind , corrections in the region of 7 nm – 10 nm are required for the speed loss . Should the aircraft be above the ideal descent profile during the initial stages of descent ( e . g . at 30,000 feet ) then there should generally be sufficient time to take the appropriate action ( e . g . using speed-brake ) to recover and regain the ideal descent profile . However , in the later stages of descent it becomes much more difficult to recover from being high on the profile due to there being less distance and time available to accomplish this . It is therefore important to understand that flight crews must use the expanded formula during the later stages of descent as the
distance required to reduce speed and the increased distance required due to a tailwind are a reality and cannot therefore be ignored . As an example , should the aircraft be at 15nm from touchdown at 5,000 feet and a speed of 250 knots , it may be thought , using the ‘ 3 times the height ’ rule , that the aircraft is perfectly on profile . However , it may prove difficult or impossible in such a case to reduce the speed to that required for landing whilst maintaining , or attempting to regain , the required final approach profile ( even more so if a tailwind exists ). This may therefore mean that either the speed reduction should be commenced earlier in order to arrive at 15nm at 5,000 feet but this time already at the minimum zero flap speed or slower , or that , if possible , the aircraft should be at 4,000 feet at 15nm and a speed of 230 knots so that the aircraft can then be flown on a very shallow descent path in order to facilitate the speed reduction and will then arrive on the ideal final approach profile at 11nm at 3,600 feet at the correct speed with the initial stages of flap deployed . When the aircraft is above the ideal descent profile the speed-brake is often used to increase the descent rate and descent angle in