Performance Class A (CS-25): Climb Theory

Take-Off Flight Path

The take-off path extends from the screen height (35 ft) to a height of 1,500 ft above the take-off surface. It is divided into four standardized segments to ensure obstacle clearance.

First Segment

• Starts: At 35 ft height ($V_2$ reached).
• Ends: When the landing gear is fully retracted.
• Configuration: Take-off flaps, Gear Down, Take-off Thrust (TOGA) on remaining engine(s).
• Requirement: Positive climb gradient (Two engines: > 0%).

Second Segment (Most Critical)

• Starts: Gear Retraction complete.
• Ends: Acceleration height (Minimum 400 ft, usually 800-1000 ft).
• Configuration: Take-off flaps, Gear Up, Take-off Thrust ($V_2$ speed).
• Requirement: Steepest climb requirement.
  • Two Engines: 2.4% gradient.
  • Three Engines: 2.7% gradient.
  • Four Engines: 3.0% gradient.

Third Segment (Acceleration)

• Starts: At acceleration height.
• Ends: When flaps are retracted and speed reaches Final Take-off Speed.
• Action: The aircraft levels off (or reduces climb) to accelerate from $V_2$ to clean speed. Flaps are retracted on schedule.
• Requirement: Capability to accelerate.

Fourth Segment (Final Climb)

• Starts: Flaps Up, Clean Speed.
• Ends: 1,500 ft net height.
• Configuration: Clean, Max Continuous Thrust (MCT).
• Requirement:
  • Two Engines: 1.2% gradient.
  • Three Engines: 1.5% gradient.
  • Four Engines: 1.7% gradient.

Net Take-Off Flight Path

For obstacle clearance calculations, the Gross flight path (what the aircraft actually flies) is reduced by a safety margin to create the Net flight path.

• Reduction: 0.8% gradient (Two engines), 0.9% (Three), 1.0% (Four).
• Obstacles: The Net flight path must clear all obstacles by at least 35 ft vertically.