Performance Class A (CS-25): Take-off Data Application
Regulated Take-Off Weight (RTOW)
The maximum weight for take-off is the lowest of:
- Field Limit: Defined by runway length (TODR, ASDR) and slope.
- Obstacle Limit: Defined by the net flight path clearing obstacles.
- Tyre Speed Limit: Maximum ground speed for tyres.
- Brake Energy Limit: Maximum energy brakes can absorb during RTO.
- Structural Limit: Maximum Take-Off Mass (MTOM) defined by the manufacturer.
- Climb Limit: Ability to meet the 2.4% WAT (Weight, Altitude, Temperature) climb gradient in the 2nd segment.
Line-Up Allowance
Performance calculations assume the take-off starts at the beginning of the runway. However, aircraft need space to line up.
- Adjustment: A "Line-Up Allowance" (LUA) distance must be subtracted from the TORA/ASDA to account for the runway length consumed during line-up.
- Values: vary by aircraft size and line-up angle (90° vs 180° turn). E.g., 90° entry might use less runway than a 180° turn on the runway.
Simplified Take-Off Analysis
Charts usually provide corrections for:
- Wind: Headwind increases RTOW, Tailwind decreases it significantly.
- Pressure Altitude: Higher altitude $\rightarrow$ lower engine thrust $\rightarrow$ lower RTOW.
- Temperature: Higher temperature $\rightarrow$ lower thrust $\rightarrow$ lower RTOW.
- Slope: Downslope assists acceleration (higher RTOW), upslope hinders.
- Runway Surface: Wet/Contaminated reduces screen height to 15 ft (for wet) and degrades stopping performance.
V-Speed Determination
Once the actual Take-Of Weight (TOW) is known (and confirmed $\le$ RTOW), the V-speeds ($V_1, V_R, V_2$) are extracted from the tables/FMS based on:
- Actual Weight.
- Flap Setting.
- Pressure Altitude & Temperature.
- Runway Condition (Wet runway often requires a lower $V_1$ to improve stopping capability).