Donald Neuhaus

The FCU is subject to Fuel System Limitations (FSL) as defined in FAA AC 25.981-1B. FSLs are a means of identifying certain design configuration items related to fuel tank ignition source prevention features and Lightning /HIRF protection that require periodic inspection. An Equivalent Level of Safety (ELS) for Continued Airworthiness of the FCUs has previously been developed. The ELS requires a 10,000 FH interval “Safe-Life” test which includes a physical inspection of the FCU electrical components identified as having latent failure modes, and discovery of any overheating, charring, debris, or other suspicious conditions on the interior or exterior of the FCU. While returned units are routinely subjected to normal functional tests, the “Safe- Life” test and inspection contains additional electrical testing (i.e. tank short circuit protection testing) and physical inspections above and beyond the normal functional tests performed on returned units. Only if an FCU was (1) returned under a previous agreement to perform this 10,000 FH Safe Life Test, or (2) with an explicit request to perform this specific testing, can we be sure that both the additional testing and inspection have been performed and the FCU marked IAW the Service Bulletin.