Narrative:

I was notified by my supervisor that an aircraft was coming in from ZZZ with a broken tamper seal on the forward lavatory O2 mask door. Our initial thought was that we needed to replace the broken seal. We later discovered that a seal is not required and that the tsa in ZZZ had put it on. I questioned maintenance control and they were aware of it and allowed the plane to fly with this seal in place. We took a lengthy delay investigating this and in the end we removed the seal; opened the O2 door and verified that the masks were packed correctly and re-closed the door. Today; another aircraft had the same issue; however; this time we did not know about it ahead of time. Apparently a fleet service supervisor told one of our technicians about the tape this time and I was notified just before push time. This time the seal was not broken so the forward lavatory O2 mask door was disabled. Again we removed the seal and inspected the mask installation. I can't believe the airline or the FAA would allow undocumented maintenance on one of our aircraft; resulting in a disabled emergency O2 system. Supplemental info from acn 825075: after departure; ZZZ flight attendant; upon using the forward lavatory; discovered an adhesive security seal with company logo on it and a seal number applied to the forward lavatory emergency oxygen mask drop down door in the lavatory ceiling which effectively rendered the emergency oxygen mask inoperative in the forward lavatory. Flight attendant conferred with 'a' flight attendant who was also unaware of the seal on the drop down door. They cut the seal with a fingernail to permit the drop down door to function inflight. A flight attendant remembered that 5 minutes prior to departure door closing at ZZZ; a tsa official boarded the aircraft showing his credentials as authority to board and entered the forward lavatory then exited the aircraft. Immediately thereafter; a company csa boarded the aircraft and entered the forward lavatory explaining to the 'a' flight attendant that she needed to record a seal number. The 'a' flight attendant saw no seal present at that moment (did not look at the ceiling) and assumed the seal had been on the forward lavatory access panel under the sink and had been removed. If it is necessary to seal the emergency oxygen drop down doors in the lavatories or in the cabin; the crews must be informed so that these can be preflight inspected.

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Original NASA ASRS Text

Title: A B737 Mechanic and Captain report placement of a security seal on a lavatory oxygen mask door; which will render the emergency oxygen system in the lavatory inoperative.

Narrative: I was notified by my supervisor that an aircraft was coming in from ZZZ with a broken tamper seal on the forward lavatory O2 mask door. Our initial thought was that we needed to replace the broken seal. We later discovered that a seal is not required and that the TSA in ZZZ had put it on. I questioned Maintenance Control and they were aware of it and allowed the plane to fly with this seal in place. We took a lengthy delay investigating this and in the end we removed the seal; opened the O2 door and verified that the masks were packed correctly and re-closed the door. Today; another aircraft had the same issue; however; this time we did not know about it ahead of time. Apparently a Fleet Service Supervisor told one of our Technicians about the tape this time and I was notified just before push time. This time the seal was not broken so the forward lavatory O2 mask door was disabled. Again we removed the seal and inspected the mask installation. I can't believe the Airline or the FAA would allow undocumented maintenance on one of our aircraft; resulting in a disabled emergency O2 system. Supplemental info from ACN 825075: After departure; ZZZ Flight Attendant; upon using the forward lavatory; discovered an adhesive security seal with company logo on it and a seal number applied to the forward lavatory emergency oxygen mask drop down door in the lavatory ceiling which effectively rendered the emergency oxygen mask inoperative in the forward lavatory. Flight Attendant conferred with 'A' Flight Attendant who was also unaware of the seal on the drop down door. They cut the seal with a fingernail to permit the drop down door to function inflight. A Flight Attendant remembered that 5 minutes prior to departure door closing at ZZZ; a TSA official boarded the aircraft showing his credentials as authority to board and entered the forward lavatory then exited the aircraft. Immediately thereafter; a company CSA boarded the aircraft and entered the forward lavatory explaining to the 'A' Flight Attendant that she needed to record a seal number. The 'A' Flight Attendant saw no seal present at that moment (did not look at the ceiling) and assumed the seal had been on the forward lavatory access panel under the sink and had been removed. If it is necessary to seal the emergency oxygen drop down doors in the lavatories or in the cabin; the crews must be informed so that these can be preflight inspected.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.