getting to grips with aircraft performance 如何掌握飞机性能 1(37)

On a wet or contaminated runway, the screen height (height at the end of the TOD) is 15 feet. The net takeoff flight path starts at 35 feet at the end of the TOD. So, the gross flight path starts at 15 feet while the net flight path starts at 35 feet at the end of the TOD (see Figure C28).
“IEM-OPS 1.495 When taking off on a wet or a contaminated runway and an engine failure occurs at V1, this implies that the aeroplane can initially be as much as 20 ft below the net takeoff flight path, and therefore may clear close-in obstacles by only 15 ft”.

While the net flight path clears the obstacles by 35 feet all along the takeoff flight path, the gross flight path can initially be at less than 35 feet above close-in obstacles.
5.5.4.4. Takeoff Weight
The TOD and ASD requirements differ between wet and contaminated runways on one side, and dry runways on the other side.
Indeed, on wet and contaminated runways, the screen height is measured at 15 feet rather than 35 feet on dry runways. Moreover, the use of reverse thrust is allowed for ASD determination on wet and contaminated runways, whereas it is forbidden to take it into account for the ASD determination on dry runways.
Therefore, it is possible to obtain shorter TODs and ASDs on wet and contaminated runways than on dry runways for the same takeoff conditions. Thus, it is possible to obtain higher takeoff weights on surfaces covered with water, slush, or snow than on dry runways. This is why the regulation indicates that:

“JAR-OPS 1.490 (b)(5) On a wet or contaminated runway, the takeoff mass must not exceed that permitted for a takeoff on a dry runway under the same conditions”.
6. MAXIMUM TAKEOFF WEIGHT DETERMINATION
6.1. Speed Optimization Process
Airbus recommends that the MTOW on a given runway and given conditions be computed by optimizing both the V1/VR ratio and the V2/VS ratio.
The performance software provided by Airbus automatically carries out this optimized computation, whose aim is to achieve the highest possible MTOW. This optimization process is described in Appendix 2 of this manual.

6.2. Regulatory Takeoff Weight Chart (RTOW Chart)
To determine the regulatory takeoff weight for repetitive takeoff planning, it is mandatory to provide pilots with data, which enable quick calculations of the Maximum Allowed Takeoff Weight and its associated speeds. This can be done via ground or onboard computerized systems, such as the LPC (Less Paper Cockpit: see Appendix 3), or through paper documents.
These paper documents are referred to as “Regulatory TakeOff Weight” charts (RTOW). The charts must be generated for each runway heading, and can be produced for different takeoff conditions at the convenience of the applicant (temperature, wind, QNH, flap setting, runway status, inoperative items).
　
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