Title: [Industrial Standard] On the differences of airworthiness standards of piston engines in civil aviation (3)

When examining the international cooperation projects, especially the piston engine projects cooperating with Europe, our airworthiness authorities should list the differences of the technical requirements in Table 2 of "On the difference of airworthiness standards of piston engines in civil aviation (2)" as the targets of examination. The differences shown in items 1-10 may result in differences in model design and use restrictions approved during model approval.

1)Structural integrity of rotor

CCAR33-R2 evaluates the structural integrity of the piston engine disk in accordance with that of the turbine engine rotor, determines the critical stage rotor and the test boundary conditions such as the highest speed and temperature, and carries out the 5-minute over-rotation test. CS-E change4 does not require the structural integrity of the piston engine rotor, but rather the non-containment of equipment with high-energy rotors that fails without causing severe high-energy debris, or the acceptable level of design integrity including high-energy parts. That is, for the structural integrity of rotor, CAAC requires a rotor over-rotation test which EASA does not specify, allowing a greater degree of compliance with the results of safety analysis.

2)Failure analysis

CCAR33-R2 does not have specific requirements for failure analysis clause, but those for the relevant safety analysis can be found in some clauses such as concerning control system and instrument connection. CS-E change 4 specifically requires failure analysis of all manual and automatic controls of engines in typical installed conditions, such as engine components and control systems that may affect the function and integrity of the main rotating components, so as to determine that there are no single point faults or double faults that may cause an engine unsafe condition beyond the normal control range of the flight crew. In terms of the requirements for failure analysis, EASA requirements are more comprehensive.

3)Rotor containment

CCAR33-R2 requires that the turbocharger must contain all the debris from the compressor and turbine failure at the highest normal speed. CS-E change 4 only requires blade containment and allows for three stages of hub fracture within normal operating speeds (i.e. the highest allowable rotational speed free from fault in the system), but requires quality control of containment methods, critical part approval life and quality control, rotor integrity testing, clearance analysis and safety analysis between the stationary parts jointly to ensure the safety of the high-energy rotor equipment. The requirements for clearance analysis between stationary parts is not involved in CCAR33-R2, which requires that the maximum displacement due to thermal expansion and contraction or displacement due to failure of stator or rotor parts will not cause any harm to engine. Besides, EASA allows that results of probability analysis such as the above-mentioned probability of a hub fracture event to be used to illustrate that the rotor is unlikely to rupture with hazardous consequences.

The differences between items 11-13 in Table 2 of “On the differences of airworthiness standards of piston engines in civil aviation (2)” do not change the model design itself and the approval manual, nor do they change the use restriction to meet the requirements of different standards. But they will result in another approach to compliance due to different requirements for specific design and test verification.

Some opinions

The US Federal Aviation Administration (FAA) and the European Aeronautics and Security Agency (EASA) established airworthiness bilateral relations more than 70 years ago, and the process of model review is relatively simple based on mutual trust. China and the United States have also established airworthiness bilateral relations on some aviation products, and the standards are basically the same, so there will hardly be many problems about the requirements and review procedures in the airworthiness certification process. However, China and Europe have not yet established a bilateral airworthiness system, and the two standard systems are so different, particularly in terms of aero engine airworthiness requirements, that they will increase the difficulty of cooperation and airworthiness review between China and European countries. Therefore, to investigate and evaluate the differences of airworthiness standards between China, Europe and the United States can help put forward the key points of airworthiness certification, further providing suggestions and guidance for the Civil Aviation Administration of China (CAAC) in the airworthiness certification of international cooperation projects and the applicants in the certification process of international cooperation projects.

The General Office of the State Council this year issued "Guiding Opinions on Promoting the Development of General Aviation Industry," which emphasized the importance of deepening international cooperation and innovative cooperation in the process of promoting industrial transformation. However, it should be pointed out that original equipment manufacturers (OEM) or model certificate (TC) applicants need to be equipped with the integration technology of the whole machine, the core technology of the overall design and the management and control capacity of the suppliers to ensure that the process of product development and verification of compliance with airworthiness regulation is not subject to the partners. Therefore, it is the absolute principle as well as the real goal to consolidate its own foundation and improve the industrial design and manufacturing level. The department of airworthiness certification should pay attention to tracking and studying the development trends of global airworthiness standards in order to gradually improve airworthiness standard system, promote international exchanges and establish regular communication mechanisms with the European and American airworthiness authorities on the formulation and revision of airworthiness standards. As a result, technical cooperation with European and American airworthiness authorities can be activated in technology and research airworthiness certification, comprehensively enhancing our airworthiness certification capacity and meeting the increasing demand for navigation development.

By Gao Yanlei from Engine Certification Center