INDICATING/RECORDING SYSTEM, Erroneous Illumination of Cabin Altitude Warning Lights in High Altitude Landing Mode

FAA Aviation Safety SPECIAL AIRWORTHINESS INFORMATION BULLETIN SUBJ: INDICATING/RECORDING SYSTEM, Erroneous Illumination of Cabin Altitude Warning Lights in High Altitude Landing Mode SAIB: 2025-08 Date: September 8, 2025 This is information only. Recommendations aren’t mandatory.

Introduction

This Special Airworthiness Information Bulletin (SAIB) advises owners and operators of The Boeing Company Model 737-700 and 737-800 series airplanes with the serial numbers listed in Table 1 of erroneous illumination of cabin altitude warning lights in high altitude landing mode and recommended actions.

Table 1 – Affected Airplane Serial Numbers 29268 33079 33500 34809 29971 33080 33542 35212 30462 33361 33986 35224 32575 33434 33987 35238 32777 33474 34260 36090 32916 33476 34477 36106 32970 33477 34807 36714 33010 33499 34808 36852

At this time, the airworthiness concern is not an unsafe condition that would warrant airworthiness directive (AD) action under Title 14 of the Code of Federal Regulations (14 CFR) part 39.

Background

The FAA published AD 2013-02-05, Amendment 39-17326 (78 FR 6202, January 30, 2013) (AD 2013-02-05), and AD 2015-21-11, Amendment 39-18304 (80 FR 65927, October 28, 2015) (AD 2015-21-11). These ADs require changes to improve reliability of the cabin altitude warning system (CAWS) by adding a redundant cabin altitude pressure switch and replacing the aural warning module (AWM) with a new or reworked module with redundant inputs. AD 2013-02-05 requires installing two warning level indicator lights on both P1-3 and P3-1 instrument panels in the flight compartment, and, as applicable, replacing the existing P5-16 and P5-10 panels, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-31A1332, Revision 3, dated March 28, 2012. AD 2015-21-11 requires modifying the instrument panels, installing light assemblies, modifying the wire bundles, and installing a new circuit breaker, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-31A1332, Revision 3, dated March 28, 2012; or as of September 15, 2015, Boeing Alert Service Bulletin 737-31A1332, Revision 4, dated October 31, 2013. Both AD 2013-02-05 and AD 2015-21-11 also provide credit for actions performed before the effective dates of those ADs using Boeing Alert Service Bulletin 737-31A1332, Revision 1, dated June 24, 2010; or Boeing Alert Service Bulletin 737-31A1332, Revision 2, dated August 18, 2011.

Boeing Alert Service Bulletin 737-31A1332, Revision 1, dated June 24, 2010; Boeing Alert Service Bulletin 737-31A1332, Revision 2, dated August 18, 2011; and Boeing Alert Service Bulletin 737-31A1332, Revision 3, dated March 28, 2012; contain incorrect wiring and/or omission or deletion of wire W2508-0032-22 to pin 9 of the P5-16 cabin altitude module. When operating in high altitude mode, this invalid wiring configuration will result in the CAWS lights illuminating erroneously when cabin altitude exceeds 10,000 feet rather than the high elevation limit. To correct the error in these service bulletins, Boeing published Boeing Alert Service Bulletin 737-31A1332, Revision 4, dated October 31, 2013; and Boeing Alert Service Bulletin 737-31A1332, Revision 5, dated October 31, 2017; which add the W2508-0032-22 wire.

Recommendations

The FAA recommends that all owners and operators of the affected airplanes accomplish steps 34 and 35 of the Work Instructions for Groups 8 through 21, 30 through 36, and 40 (airplanes with the high altitude landing configuration of the cabin altitude warning system) of Boeing Alert Service Bulletin 737-31A1332, Revision 5, dated October 31, 2017, at the earliest opportunity, unless the functional test of the cabin altitude warning system has already been accomplished using steps 30 and 31 of the Work Instructions for Groups 8 through 21, and 30 through 33 (airplanes with the high altitude landing configuration of the cabin altitude warning system) of Boeing Alert Service Bulletin 737-31A1332, Revision 4, dated October 31, 2013.

For Further Information Contact

Nicole Tsang, Aviation Safety Engineer, 2200 South 216th Street, Des Moines, WA 98198; phone: 206-231-3959; email: [email protected].

For Related Service Information Contact

Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; phone: 562-797-1717; website: myboeingfleet.com.