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.

Step Heights:

  • 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.

Variables:

  • 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

Corrections:

  • If high fly at max IAS (more drag)
  • If low fly slower than 280KT down to 250KT (improve ‘glide’)

Credit to ‘Jetguy, 411A and PPGMD’ on Airliners.net for the above info. I’ve put all of the above information into PDF format which can be downloaded from the Download page.

Hope it helps,

Chris