## 5 Aircraft Performance Regulations
### Contaminated Runway Regulations  
Recommendations for the effect of contaminants on runways is presented in the Aeroplane Performance Manual [87], based on the European Union Aviation Safety Agency (EASA) aircraft braking performance models [88]. These models provide levels of assumed surface friction coefficient available to the aircraft tire during landing on contaminated runways for different anti-skid braking systems (Table 5). RWYCC 0 corresponds to minimal or non-existent braking action; hence, no wheel braking coefficient in those conditions is applicable. The wheel braking coefficients presented in Table 5 correspond to the pilot report of runway braking action in Table 4. These values, however, are not related to particular aircraft models or aircraft and landing parameters. Figure 15: ICAO standards and regulations in regard to aircraft braking performance. Braking coefficients for RWYCC 5 are presented in Figure 16. Equations from [88] and [87] are presented graphically for simplicity and comparison. The assumed braking coefficient also depends on the tire pressure [88]. To determine the braking coefficient for a specific RWYCC and aircraft ground speed, the maximum braking coefficient is multiplied by the efficiency number of the anti-skid system, which can be defined during the anti-braking system tests. According to EASA, there are two methods for the evaluation of the anti-skid system efficiency value: the torque method and the wheel-slip method [88]. Both of these methods should be performed on a wet smooth runway, with worn tires, and the highest reasonable landing tire pressure, at different speeds and under different brake energy conditions. The approximate efficiency values for different types of anti-skid systems according to ICAO are presented in Table 6.  
The on-off systems are the simplest types of anti-skid systems. For these systems, the brake is applied, and the pressure then releases when the wheel is locked. After the wheel \begin{table}
\begin{tabular}{c c} \hline \hline
**Type of Anti-Skid System** & **Efficiency Value** \\ \hline On-off & 0.30 \\ Quasi-modulating & 0.50 \\ Fully modulating & 0.80 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Efficiency values of anti-skid systems [87]. Figure 16: Maximum braking coefficient for RWYCC 5 [88]. \begin{table}
\begin{tabular}{c c} \hline \hline
**RWYCC** & **Wheel Braking Coefficient** \\ \hline
6 & 90 per cent of certified value \\
5 & According to Figure 16 for a smooth (ungrooved and not textured) wet runway \\
4 & 0.20 \\
3 & 0.16 \\  & 50 per cent of the value obtained for RWYCC 5 for speeds \\
2 & below 85 per cent of the aquaplaning speed and 0.05 for speeds above 85 per cent of the aquaplaning speed \\
1 & 0.07 \\
0 & Not applicable \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Wheel braking coefficients for RWYCC numbers [88]. accelerates back to synchronous speed, the full pressure is applied again [89]. This cycle is repeated throughout the stop, or until the wheel ceases to skid with the applied brake pressure. Quasi-modulating systems are an improvement of on-off systems and regulate the brake pressure continuously, as a function of wheel speed [89]. Typically, brake pressure is released when the wheel deceleration rate exceeds a preselected value. Brake pressure is reapplied at a lower level after a length of time, appropriate to the severity of the skid. Brake pressure is then gradually increased until another incipient skid condition is sensed. In general, the corrective actions taken by these systems to exit the skid condition are based on a pre-programmed sequence, rather than the wheel speed time history. Fully modulating systems are a further refinement of the quasi-modulating systems [89]. The major difference between these two types of anti-skid systems is in the implementation of the skid control logic. During a skid, corrective action is based on the sensed wheel speed signal rather than a preprogrammed response.