Of course, using the aircraft’s VNAV function will give you a precise Descent Point at your requested Descent Rate – but if it’s not available then the following will help.
Disclaimer: While the procedures described here closely replicate those in real life, they must only be used for home flight simulator purposes!
In simple terms:
- Descent Point (DP) = 3 x your required altitude loss (in 1000s of feet)
- Descent Rate (DR) = 5 x your Ground Speed (GS)
For example: If you cruise at FL290 and want descend with a GS of 350kt to a level of 3000ft (ignoring pressure setting differences between FL and AMSL) then…
DP = (29000 – 3000 = 26) x 3 = 78nm
DR = 350 x 5 = 1750fpm
For easier mental math, DR can also be calculated by halving GS then multiplying by 10.
- Descent: 90nm/FL300, 60nm/FL200, 45nm/FL150, 30nm/FL100 (slowing for 250KIAS)
- Approach: 10nm/3000ft, 5nm/1500ft, 3nm/1000ft, 2nm/600ft, 1nm/300ft (all heights AGL)
If your range isn’t to the threshold add 1nm to the approach ranges to compensate.
- Head/Tailwind (50KT) = DP +/- 10nm (tailwind = +10nm)
- Heavy Aircraft (MLW) = DP + 10nm
- Light Aircraft = DP – 10nm
- Final approach in direction of descent (e.g. ILS) = DP + 10nm
- Final approach reciprocal to direction of descent = DP – 10nm
- Start to configure flaps no later than 20nm from destination
- If high fly at max IAS (more drag)
- If low fly slower than 280KT down to 250KT (improve ‘glide’)
Hope it helps,