Aircraft
Certification Service Washington, DC U.S. Department of Transportation Federal Aviation Administration
NM-07-52
September 24, 2007
This is information only. Recommendations
aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) informs you - a
manufacturer of smoke detectors, a manufacturer of commercial
airplanes, or a registered owner or operator of a transport category
airplane - that lavatory ionization fire/smoke detectors installed in
airplanes may provide a false warning (“false warn”) if the cabin is
over-pressurized.
Background
The FAA received a report of a “false warn” of an ionization smoke
detector installed in a lavatory. The “false warn” occurred during an
approach to an airport and after landing. The airworthiness provisions
do not require that lavatory smoke detectors meet the provisions in
Technical Standard Order (TSO) TSO-C1d, which applies to cargo
compartment smoke detectors. The TSO requires that tests be conducted
to ensure that no “false warn” occurs when subjected to sudden cabin
pressure decrease or increase.
During this event, the cabin air pressure was over-pressurized and, for
a portion of the event, the cabin pressure was greater than sea-level
pressure. Both during approach and after landing, the detector did
“false warn.” Even though flight attendants confirmed that there was no
smoke in the lavatory, this false warning added confusion, which
resulted in the crew initiating an emergency evacuation while the cabin
was over-pressurized. The root cause of the “false warn” was the
overpressurization event, which was due to debris lodged in the cabin
air pressure regulator valves. This prevented normal control of the
cabin pressure. Appropriate maintenance actions should prevent cabin
over-pressure problems. This SAIB provides awareness to the crew of
lavatory smoke detector sensitivity.
Recommendations
The FAA would like crew members to be aware that in the event the cabin
is over-pressurized, airplane lavatory ionization smoke detectors could
“false warn.” In such cases, good crew management and communications
between flight deck crew and cabin attendants is needed to ensure that
correct action is taken. Airlines should incorporate this note in their
Flight Crew Operations Manuals (FCOM) and Flight Attendant Manuals
(FAM) / Cabin Crew Manuals (CCM).
For Further Information Contact
Stephen Happenny, Aerospace Engineer, Transport Standards Staff,
1601 Lind Avenue SW., Renton, Washington 98057-3356; telephone (425)
227-2147; fax (425)-227-1320. E-mail: Stephen.happenny@faa.gov