1 Strength
1.1 Compliance with CS 25.1309(b) in relation to leakage in ducts and components will be achieved if it is shown that no hazardous effect will result from any single burst or excessive leakage.
1.2 Each element (ducting and components) of a system, the failure of which is likely to endanger the aeroplane or its occupants, should satisfy the most critical conditions of Table 1. TABLE 1
| Conditions 1 | Conditions 2 |
|---|
| 1·5 P1 at T1 | 3·0 P1 at T1 |
| 1·33 P2 at T2 | 2·66 P2 at T2 |
| 1·0 P3 at T3 | 2·0 P3 at T3 |
| – | 1·0 P4 at T4 |
P1 = the most critical value of pressure encountered during normal functioning. T1 = the combination of internal and external temperatures which can be encountered in association with pressure P1. P2 = the most critical value of pressure corresponding to a probability of occurrence ‘reasonably probable’. T2 = the combination of internal and external temperatures which can be encountered in association with pressure P2. P3 = the most critical value of pressure corresponding to a probability of occurrence ‘remote’. T3 = the combination of internal and external temperatures which can be encountered in association with pressure P3. P4 = the most critical value of pressure corresponding to a probability of occurrence ‘extremely remote’. T4 = the combination of internal and external temperatures which can be encountered in association with pressure P4.
1.3 After being subjected to the conditions given in column 1 of Table 1, and on normal operating conditions being restored, the element should operate normally and there should be no detrimental permanent distortion.
1.4 The element should be capable of withstanding the conditions given in column 2 of Table 1 without bursting or excessive leakage. On normal operating conditions being restored, correct functioning of the element is not required.
1.5 The element should be capable of withstanding, simultaneously with the loads resulting from the temperatures and pressures given in the Table, the loads resulting from – a. Any distortion between each element of the system and its supporting structures. b. Environmental conditions such as vibration, acceleration and deformation.
1.6 The system should be designed to have sufficient strength to withstand the handling likely to occur in operation (including maintenance operations). 2 Tests
2.1 Static tests. Each element examined under 1.2 should be static-tested to show that it can withstand the most severe conditions derived from consideration of the temperatures and pressures given in the Table. In addition, when necessary, sub-systems should be tested to the most severe conditions of 1.2 and 1.5. The test facility should be as representative as possible of the aircraft installation in respect of these conditions.
2.2 Endurance tests. When failures can result in hazardous conditions, elements and/or sub-systems should be fatigue-tested under representative operating conditions that simulate complete flights to establish their lives.