Performance Class A (CS-25): Approach and Landing Theory
Climb Requirements
Approach Climb (OEI)
During an approach (one engine inoperative), if a Go-Around is initiated:
- Configuration: Approach Flaps, Gear Up, OEI, Take-off Thrust.
- Gradient Requirement:
- Two Engines: 2.1%.
- Three Engines: 2.3%.
- Four Engines: 2.4%.
Landing Climb (AEO)
Also known as "Balked Landing" (Go-Around from very low altitude/touchdown).
- Configuration: Landing Flaps, Gear Down, AEO, Take-off Thrust.
- Gradient Requirement: 3.2% (for all aircraft types).
- This ensures the aircraft can climb away safely even in full landing configuration.
Landing Distance Required (LDR)
The horizontal distance from a screen height of 50 ft to a complete stop.
Operational Factors (Dispatch)
At the planning stage (Dispatch), the aircraft must be able to land within a fraction of the available runway density (LDA).
- Dry Runway: LDR $\le 60\%$ of LDA (or LDA $\ge 1.67 \times$ LDR).
- Wet Runway: LDR $\le 60\%$ of LDA, then multiply the required distance by 1.15.
- Result: LDA $\ge 1.92 \times$ LDR Dry.
In-Flight Calculation
Once in flight, for the actual landing, the "In-Flight" or "Advisory" landing distance is used (often called ALD or OLD). This removes the large 1.67 safety factor but adds a smaller operational margin (e.g., +15%).
Factors Affecting LDR
- Mass: Higher mass $\rightarrow$ higher $V_{REF}$ $\rightarrow$ longer distance. ($Distance \propto Mass^2$).
- Altitude: Higher density altitude $\rightarrow$ higher TAS for same IAS $\rightarrow$ longer distance.
- Wind: Tailwind increases distance significantly.
- Slope: Downslope increases distance.
- Surface: Water/Ice/Snow reduces braking action, increasing distance.