Testing for Certification of CVMTM Sensors on the 737NG Aft Pressure Bulkhead

Boeing has invested in the development of health monitoring sensors over the years and is currently working multiple projects to implement such technology as viable inspection methods. In 2016, Boeing added Comparative Vacuum Monitoring (CVMTM) sensors as an alternative inspection method on the 737NG Center Wing Box fittings utilizing an economic service bulletin. In 2018, Boeing partnered with Anodyne Electronics Manufacturing (AEM) Corp and Delta TechOps to pursue using CVM sensors on the web of the 737NG Aft Pressure Bulkhead as an alternative inspection to Service Bulletin (SB) 737-53A1248. This is a safety bulletin due to reported in-service cracks on the 737 classic models and is mandated by the FAA with an Advisory Directive (AD). In 2022, Boeing launched the certification project. This paper will cover some of the testing that went into the certification of CVM sensors for this targeted application. Boeing has received FAA approval for their method of compliance issue paper and certification plan. Boeing has completed all tests and demonstrated that the CVM sensors are as effective as low frequency eddy current (LFEC) inspections for this application. Service Bulletin (SB) 737-53-1418 is being developed to allow operators to use CVM for this application. Boeing is currently finalizing the certification documents for submission to the FAA. CVM sensors were installed at the critical location - the web to “Y” chord attachment between stringers 5 to 7 on the left side and stringers 5 to 9 on the right side. The proposed CVM option will demonstrate equivalency to LFEC and utilize the same inspection interval. The CVM system is expected to reduce the inspection time from 24 hours to 15 minutes by eliminating the access removals (aft galley, insulation blankets) or tailcone entry, needed to allow inspector admission to conduct the traditional nondestructive inspection.