Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain McDonnell Douglas Model DC-9-81 (MD-81), DC-9-82 (MD-82), DC-9-83 (MD-83), DC-9-87 (MD-87), and Model MD-88 airplanes. This proposal would require replacement of certain freeze protection ribbon heaters in the lavatory water supply system, and flushing, cleaning, and sterilizing the potable water system; disconnecting, coiling, and stowing the wiring of the freeze protection ribbon heater; or removal of freeze protection heaters. This action is necessary to prevent failure of freeze protection ribbon heaters, which could result in the charring, scorching, smoking, and shorting out of freeze protection ribbon heaters in the lavatory water supply system. This condition, if not corrected, could also result in electrical arcing of freeze protection ribbon heaters, leading to fire and damage to water lines and components under the lavatory sink. This action is intended to addressthe identified unsafe condition.