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B-18 Page 2 of 4 D6-27370-866-EGP
Flight Crew Operations Manual Bulletin No. EGP-18 R1, Dated June 8, 2009 (continued)
To help mitigate any possible confusion associated with the B737 cabin altitude
warning system, the FAA issued AD 2006-13-13 which required changes to the
AFM procedures in Section 2 for responding to the intermittent cabin altitude/
configuration warning horn. These AFM changes and associated Flight Crew
Operations Manual (FCOM) Quick Reference Handbook (QRH) non-normal
checklist changes were intended to make it easier for flight crews to determine
whether the intermittent horn was sounding for cabin altitude or for takeoff
configuration.
The FAA believed, however, that additional interim action was necessary until
such time as the new warning lights could be fully implemented in the B737
fleet.
In mid-2008, the FAA determined that the most practical interim solution was to
issue AD 2008-23-07. This AD requires flight crews to brief cabin altitude
warning indications and procedures as part of the takeoff briefing before engine
start on the first flight of the day or following a flight crew member change. This
briefing is required in any B737 in which the CABIN ALTITUDE and
TAKEOFF CONFIG lights are not installed, or are installed but not activated.
Following further discussions, the FAA has agreed that a need exists for crews to
recognize the difference between an intermittent warning horn sounding in flight
below 10,000 feet MSL, as opposed to sounding at or above 10,000 feet MSL. In
flight below 10,000 feet MSL, the intermittent warning horn is associated with an
inflight failure of the Air-Ground Sensor switch. At or above 10,000 feet MSL,
sounding of the intermittent warning horn requires the crew to immediately don
oxygen masks and set regulators to 100%.
The FAA has therefore approved an Alternative Method of Compliance (AMOC)
to the Non-Normal Procedures mandated by AD 2006-13-13 and to the Takeoff
Briefing mandated by AD 2008-23-07. The AMOC was approved by FAA
Approval Letter 130S-09-134a dated April 28, 2009.
AD 2006-13-13
The current WARNING HORN – CABIN ALTITUDE OR CONFIGURATION
Non-Normal Procedure in the AFM will be revised as follows:
1. The title will be changed to WARNING HORN OR WARNING LIGHT –
CABIN ALTITUDE OR TAKEOFF CONFIGURATION.
2. The condition statement and the procedure will include reference to the
CABIN ALTITUDE and TAKEOFF CONFIG lights.
3. The requirement to don oxygen masks, establish crew communications and do
the CABIN ALTITUDE or Rapid Depressurization checklist will only apply if
the intermittent warning horn sounds or a CABIN ALTITUDE light illuminates
in flight at an airplane flight altitude above 10,000 feet MSL.
4. Reference to the steady horn in the condition statement will be deleted. The
corresponding step in the procedure will be deleted.
September 24, 2015
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