25.1309-1A is an Advisory Circular (AC) that describes various acceptable means for showing compliance with the requirements of 25.1309(b), (c), and (d) of the Federal Aviation Regulations (FAR). These means are intended to provide guidance for the experienced engineering and operational judgment that must form the basis for compliance findings. They are not mandatory. Other means may be used if they show compliance with this section of the FAR.

Section 25.1309(b) provides general requirements for a logical and acceptable inverse relationship between the probability and the severity of each failure condition, and section 25.1309(d) requires that compliance be shown primarily by an analysis. Section 25.1309(c) provides general requirements for system monitoring, failure warning, and capability for appropriate corrective action by the crew. Because section 25.1309(b) and (c) is a regulation of general applicability, it may not be used to replace or alter any allowed design practices or specific requirements of Part 25, and each requirement of  25.l309(b) and (c) applies only if other applicable sections of Part 25 do not provide a specific system requirement that has a similar purpose. While section 25.1309(b) and (c) does not apply to the performance, flight characteristic and structural loads and strength requirements of Subparts B and C, it does apply to any system on which compliance with any of those requirements is based.

For example, it does not apply to an airplane's inherent stall characteristics or their evaluation, but it does apply to a stall warning system used to enable compliance with 25.207. The Part 25 airworthiness standards are based on the fail-safe design concept that has evolved over the years. A brief description is provided in Paragraph 5. Section 25.1309(b) and (c) sets forth certain objective safety requirements based on this design concept. Many systems, equipment, and their installations have been successfully evaluated with regards to the applicable requirements of Part 25, including 25.1309(b), (c), and (d), without using structured means for safety assessments. However, in recent years there has been an increase in the degree of system complexity and integration, and in the number of safety-critical functions performed by systems. Difficulties had been experienced in assessing the hazards that could result from failures of such systems or adverse interactions among them. These difficulties led to the use of structured means for showing compliance with 25.1309(b). For this and other reasons, there is a need in guidance on acceptable means of compliance with 25.1309(b), (c), and (d).

ALD System Certification process (TC-Type certification for aviation) is awarded by aviation regulating bodies to aerospace manufacturers after it has been established that the particular design of a civil aircraft, engine, or propeller has met the regulating bodies' current prevailing airworthiness requirements for the safe conduct of flights under all normally conceivable conditions, Aircraft produced under a type certified design are issued a standard Airworthiness Certificate. A Type Certificate (TC) is a design approval issued by the Civil Aviation Authority (CAA) of a given country (such as the US FAA and EU EASA) when the applicant demonstrates that a product complies with the applicable regulations. The TC normally includes the type design, the operating limitations, the Type Certificate Data Sheet (TCDS), the applicable regulations, and other conditions or limitations prescribed by the CAA. Since the TC is a foundation for other approvals, including production and airworthiness approvals, ALD Services will guide and support you through the entire certification process.

Continue FAR/CS 25.1309

ALD certification process compliance with FAR/CS 25.1309