First you need to decide which is most important in the descent. Altitude constraints or Speed. In the real world ATC or the approach path (STAR) profile will dictate which of these you fly!
If altitude is the constraint then use OPEN DES in the Airbus or FLCH in the Boeing. This will achieve the desired altitude as quickly as possible with the pilot controlling the speed.
If speed is the constraint then use DES (managed path) in the Airbus or VNAV PTH in the Boeing. This will set a vertical path allowing for speed constraint profiles.
As above calculate you distance to the next altitude constrain, divide by 3 and it will give you a top of descent (TOD) for a THREE DEGREE APPROXIMATION SLOPE!. This may or may not be enough at altitude so plan accordingly.
‘Normal’ descent speed will be in the region of M0.79 (Airbus) M0.80 (Boeing) with a conversion to IAS (indicated airspeed) of 280Kts above 10,000’.
Platform height for ILS 3000’, Airfield Alt 1000’, Aircraft level 34,000’ gives you a difference to platform of 30,000’ which will give you a TOD of 100nm. Remember you MUST factor in deceleration! To slow from 280kt’s to 180kts will take at least 10mn so chuck it on! Now you have a TOD of 110nm TO THE ILS INTERCEPT POINT AT PLATFORM HEIGHT.
Select an initial V/S of 1500-2000 fpm and aim to descend to 10,000’ with about 10 miles to spare on your descent profile (10000-4000=6000 which is 18mn from ILS intercept point + 5m for decel to 250kts + 5m for ILS speed decel = 28nm from FAP is your level aiming point). Use the 5 miles to slow from 280kt’s to 250kt’s, reduce the V/S to approx 1500’ fpm and descend to the platform altitude on an intercept heading, again giving yourself a level segment to control the speed. Arm the ILS and reduce to 180kt’s taking either F1 for Airbus or F5 for Boeing using your second 5nm decel block.
Once on the localiser and glide slope at approx 10 miles, 3000’ AAL (Above Airfield Level) start reducing to 160kts for the intercept.
Intercept the glide slope, 2000’ AAL take the gear and final approach speed (Vapp) (dependent upon weight obviously but around 145kts for a heavy 777 isn’t far off and 130kts for a 320 series is also reasonable) then take final flap as the speed comes back, select approx 700-800 fpm for a 3 degree glide slope and fly to land.
The above procedure is a nice ‘by the numbers’ approach. In the real world we will adjust decent points and v/s on the go to fly a CDA (constant descent approach) with the aim being to keep the engines at idle for the entire approach. However, if you nail the basics you can embellish in the future.
Have fun!
