Aviation Investigation Report A98H0003
4.2.3 IFEN Supplemental Type Certificate Process
Based on information highlighted by this accident, the FAA has initiated many positive changes to its type certification process. However, there is one area that the Board feels requires additional consideration.
The purpose of FAR 25.1309 is to confirm that a system's design does not adversely affect the original aircraft type certificate. This investigation identified a deficiency with the provisions of FAR 25.1309, which allowed the IFEN STC ST00236LA-D system-to-aircraft integration design to be approved without confirmation that it was compliant with the aircraft's original type certificate. The Board is aware that there were other STC designs, certified in accordance with FAR 25.1309, in which the system-to-aircraft integration design introduced latent unsafe conditions with the potential to adversely impact the operation of the aircraft during emergency procedures. In some instances, the STC process allowed the intended function of certain checklist procedures during abnormal or emergency situations, to be altered without issuing an Airplane Flight Manual (AFM) supplement to advise the pilots. Although FAR 25.1309 applies to all aircraft systems, it would appear that STC designs that have been typically viewed as "non-essential, non-required"and that can be approved based on a qualitative assessment, are especially susceptible to improper integration.
The Board believes that, as currently written, FAR 25.1309 can be interpreted to allow STC approval of system-to-aircraft integration designs that are not compliant with the original type certification. Therefore, the Board recommends that:
Regulatory authorities require that every system installed through the STC process, undergo a level of quantitative analysis to ensure that it is properly integrated with aircraft type-certified procedures, such as emergency load-shedding.
Assessment/Reassessment Rating: Satisfactory in Part
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