Summary
We propose to adopt a new airworthiness directive (AD) for the products listed above. This proposed AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as:
As required by current certification standards, each transport aeroplane has passenger compartment exit signs and emergency lighting strips installed to locate the emergency exits. A number of these strips and signs are not electrically powered, but are self illuminated by means of a hydrogen isotope, known as Tritium. As this isotope decays over time, these signs will [lose] their brightness.
To remain compliant with regulations, Tritium exit signs and lighting strips should be replaced when their brightness has deteriorated below accepted levels. Currently, the Maintenance Review Board (MRB) Maintenance Planning Document does not include an inspection task for signs and strips containing Tritium.
This condition, if not detected and corrected, could result in insufficiently bright exit signs and lighting strips, preventing safe evacuation during an emergency, possibly resulting in injury to occupants. * * * * *
The proposed AD would require actions that are intended to address the unsafe condition described in the MCAI.