Starting the descent at the right point is the difference between a calm arrival and a dive with the speed brakes out. A few simple rules get you close every time.
The 3-to-1 rule
Allow 3 NM for every 1,000 ft you need to lose. Descending from FL350 to an airport at sea level means about 35 × 3 = 105 NM.
This gives a path of about 3°, the same angle as most glide slopes. The descent planner does the exact sum for any angle.
Vertical speed
To stay on a 3° path, a rough vertical speed is groundspeed × 5:
| Groundspeed | Vertical speed for 3° |
|---|---|
| 140 kt | about 700 fpm |
| 250 kt | about 1,300 fpm |
| 420 kt | about 2,200 fpm |
On final approach, this is how you check that you are on the glide path even without vertical guidance.
Allow for slowing down
You cannot descend and slow down efficiently at the same time. Many countries apply a 250 kt limit below 10,000 ft, and arrivals often have speed restrictions too. As a rough guide, allow about 1 NM in level flight for every 10 kt you need to lose, or add 5 to 10 NM to your descent distance.
Check as you go
Check your progress every few thousand feet: multiply your remaining altitude (in thousands) by three and compare it with the distance to go.
- More distance than the rule says: you are low. Reduce the descent rate.
- Less distance: you are high. Increase the descent rate, slow down earlier, or use the speed brakes.
Tailwinds stretch the distance you cover while descending. Start a little earlier when the wind is behind you, and a little later into a headwind.
Constraints on the arrival
STARs often have "at or above" and "at or below" altitudes at waypoints. Plan backwards from the lowest constraint near the airport, then check that every earlier constraint can be met. See Reading aeronautical charts.
For flight simulation and training only. Real-world procedures vary by country and operator; always follow the published charts and your local rules.
Keep reading
- Navaids and instrument approaches: VOR, NDB, DME, ILS and RNAV approaches in plain terms, and what decision altitude and minimum descent altitude mean.
- Holding patterns: How a hold is flown, the three entries, leg timing and speed limits.