Horizon Air

Paragraphs (g)(1), (g)(2), (h) & (k) all state that Service Bulletin MXH-35-240 applies “for all aircraft other than Bombardier airplanes” and Service Bulletin MXH-35-241 applies “for Bombardier airplane”. We feel the language in the proposed rule for Bombardier airplanes is miss leading and incorrect. Service Bulletin MXH-35-240 may in fact apply to Bombardier airplanes if the crew oxygen masks delivered with the airplanes were removed and replace with one of the masks listed in Service Bulletin MXH-35-240. The AD appears to only address the ‘as delivered’ condition with respect to Bombardier airplanes and does not take into account the possibility a different Intertechnique flight crew mask being installed in Bombardier airplanes. We feel the final rule should be change to state both Service Bulletins could apply to Bombardier airplanes. Paragraph (k) states in part “As of the effective date of this AD, no person may install …” We feel this sentence is in conflict with the time limitation in paragraph (g) of “within 24 months after the effective date of this AD…” If the proposed AD is adopted as written and a mask is removed after the effective date to facilitate other maintenance, paragraph (k) as it is currently written forces operator to immediately comply with the requirements of the proposed AD because the technician cannot ‘install’ a mask that is not in compliance with the proposed AD even if the requirement to inspect the mask is not due. The signoff by a technician would reference the AMM task to install the mask. We feel an FAA field inspector could interpret this install as a violation of the proposed AD if the mask is not verified as a mask outside of the affected masks listed in the service bulletin before it is put back into the airplane. The final rule should allow operators to install a mask back into the airplane within the 24 month compliance interval but not ‘replace’ a mask with a mask that does not meet the requirements of the pr