Performance Class A (CS-25): Drift-Down and Stabilizing Altitude Data

032-05-02Pablo Asensio Martínez2026-04-011 min

Service Ceiling vs. Net Ceiling

  • Gross Ceiling (OEI): The altitude where the aircraft can maintain a climb gradient of 0% (level flight) with one engine inoperative.
  • Net Ceiling (OEI): The Gross Ceiling minus a safety margin (e.g., 1.1% gradient).
    • This is the altitude used for planning obstacle clearance.
    • Since the penalty is subtracted from the climb capability, the Net Ceiling is lower than the Gross Ceiling.

Drift Down Graph analysis

Drift down charts allow the pilot to determine:

  1. Distance: How far the aircraft can travel while descending from cruise altitude to the stabilizing altitude.
  2. Time: How long the descent will take.
  3. Fuel: Fuel consumed during the maneuver.

Procedure

  1. Enter with Gross Weight at the point of engine failure.
  2. Follow the lines for ISA Deviation (Temperature).
  3. Read the Initial Altitude (Start of drift down) and Final Altitude (Net Ceiling).
  4. Read the Distance travelled.

Obstacle Check: The pilot must verify that at every point along the drift down path, the Net Altitude is at least 1,000 ft (or 2,000 ft in mountains) above the terrain.

Effect of Variables

  • Weight: Heavier aircraft $\rightarrow$ Steering descent $\rightarrow$ Lower Net Ceiling $\rightarrow$ Shorter Drift Down range.
  • Temperature: Higher ISA deviation (Hotter) $\rightarrow$ Lower engine thrust $\rightarrow$ Lower Net Ceiling.
  • Wind: Tailwind increases ground distance covered during drift down; Headwind decreases it.