Descent

[Bubblehead]

A jet passenger aircraft flying at 32,000 feet, at what distance from its destination will the aircraft start its descent? Is the descent a steady shallow descent, or is it done in stages in altitude?

[Splinter562]

Modern airliners typically use an idle thrust descent profile. The distance varies from aircraft to aircraft or even for the same aircraft under different conditions. From an aircraft performance standpoint, a straight-shot descent is the best option. However, the stages of the descent are dictated by ATC flows and traffic conditions.

For a simple estimate, you can use either a 3:1 or 4:1 rule (I've heard both.) Count on needing 3 to 4 miles for every 1,000 ft of descent.

For a real-world example problem for a 737-200:
Pressure Altitude: 34,000 ft MSL
Initial Approach Fix Altitude: 6,000 ft MSL
No Wind
Gross Weight: 80,000 lbs

Distance Required: 60 NM

[C]

All depends on where you are. A rough rule of thumb is treble your altitude, so if you're cruising at FL330, then roughly 100miles (33x3), or 15000ft, 45 miles (15x3). As Splinter says though it all depends where you are. For example going into a major  international airport in busy airspace you may get several step descents, starting at a couple of hundred miles out. If you're in the middle of nowhere, then you can often expect a continual descent.