Summary
We propose to adopt a new airworthiness directive (AD) for certain The Boeing Company Model 777-200 and -300 series airplanes. This proposed AD was prompted by reports of unreliable performance of the water and fuel scavenge system; failure of the fuel scavenge function can cause trapped fuel, resulting in unavailable fuel reserves. This proposed AD would require incorporating operating limitations, or modifying the water and fuel scavenge systems in the fuel tanks and certain electrical panels. We are proposing this AD to address the unsafe condition on these products.