FUEL QUANTITY INDICATOR AND LOW-FUEL LEVEL WARNING
This AMC provides guidance in the case where the fuel quantity indicator and the low-fuel warning device are not fully independent.
AC 29.1305 provides guidance that supports the use of specific instruments that do not meet the principle of independence (integrated avionics, ECAS, etc.). However, it does not provide guidance regarding the independence between the fuel quantity sensor and the fuel low-level sensor.
The fuel quantity sensor and the fuel low-level sensor should be independent. However, it is considered to be acceptable to place them on the same supporting structure providing that the following design precautions are ensured:
(a) They are electrically independent. Each sensor should be connected to the aircraft systems via a dedicated connector and a dedicated harness;
(b) A test capability is provided for each sensor to preclude an associated latent failure; and
(c) It is demonstrated by tests such as equipment qualification tests, slosh and vibration tests as requested in CS 29.965, analysis (such as safety analysis, particular risk analysis, zonal safety analysis, comparison with a fully independent design), or a combination thereof that no common modes can lead to the most severe hazard determined in CS 29.1305(a)(4)(ii).
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