# Performance Class A (CS-25): Climb Theory

> The four segments of the take-off flight path with one engine inoperative.

- **Subject:** 032 — Performance
- **Section:** 032-04 — CS-25-Applicable Operational Requirements Performance Class A – Theory
- **Topic code:** 032-04-02
- **Last reviewed:** 2026-04-01
- **Author:** Pablo Asensio Martínez
- **HTML version:** https://pilotsyllabus.com/en/performance/cs-25-applicable-operational-requirements-performance-class-a-theory/climb/

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## 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.

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Free study notes from pilotsyllabus.com. Not a substitute for training at an approved ATO.