Climb, Cruise, and Descent Performance
This domain tests whether you can plan the vertical profile: how fast and how steeply the aircraft climbs, how efficiently it cruises, and where the descent should begin.
Climb
- Climb gradient % = 100 × (Thrust − Drag) ÷ Weight. Rate of climb = excess power ÷ weight.
- Gradient matters for obstacle clearance; rate matters for time to altitude.
- V_X gives maximum angle, V_Y maximum rate. A cruise climb trades gradient for speed, cooling and visibility.
Cruise
- Specific range = TAS ÷ fuel flow, in nm per kg or per lb.
- Maximum range occurs near L/D_max, corrected for wind. Long-range cruise gives about 99% of maximum range for roughly a 1% speed penalty.
- Choose altitude using temperature, wind, mass, turbulence and the tropopause; step-climb as fuel burns off.
Descent
- The 3:1 rule: distance in nm = height in ft ÷ 1,000 × 3. A 3° path is about 318 ft/nm.
- Required rate (fpm) = ground speed (kt) × gradient (ft/nm) ÷ 60.
Worked example
FL350 to 4,000 ft is 31,000 ft. The 3:1 rule gives 93 nm. At 420 kt ground speed that is 7 nm/min, so the descent takes 13.3 min and requires about 31,000 ÷ 13.3 = 2,330 fpm.
Traps
- Using TAS instead of ground speed in descent planning.
- Forgetting the deceleration segments and the level-off.
- Ignoring wind when computing top of descent.
- Assuming the 3:1 rule works for every required gradient.