AD 2021-07-17 Airworthiness Directives; The Boeing Company Airplanes

Models named: 737-900ER series. Read the applicability below — it usually turns on serial or part numbers too.

This AD applies to all The Boeing Company Model 737-900ER series airplanes, certificated in any category.

Comply with this AD within the compliance times specified, unless already done.

Within 24 months after the date of issuance of the original airworthiness certificate or the date of issuance of the original export certificate of airworthiness or 12 months after the effective date of this AD, whichever is later: Do the actions required by paragraph (g)(1) or (2) of this AD. (1) Determine airplane exposure to runway deicing fluids containing potassium formate or potassium acetate by reviewing airport data on the types of components in the deicing fluid used at airports that support airplane operations. (i) If the airplane has not been exposed: Repeat the requirements specified in paragraph (g)(1) of this AD thereafter at intervals not to exceed 24 months. (ii) If the airplane has been exposed: Within 90 days after that determination is made, do the inspection required by paragraph (g)(2) of this AD. Repeat the inspection thereafter at intervals not to exceed 24 months. (2) Do a detailed inspection of the electrical connectors, including the contacts and backshells of the line replaceable unit (LRU) in the wheel well of the MLG, for corrosion in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-24A1148, Revision 2, dated September 14, 2020. Perform applicable corrective actions at the applicable times, as specified in paragraphs (g)(2)(i) through (iii) of this AD, in accordance with the Accomplishment Instructions of Boeing Alert Service Bulletin 737-24A1148, Revision 2, dated September 14, 2020. Repeat the inspection thereafter at intervals not to exceed 24 months. For the purposes of this AD, a detailed inspection is defined as an intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required. (i) If the total backshell surface area corrosion is 10 percent or less, clean the backshell(s) before further flight. (ii) If the total backshell surface area corrosion is greater than 10 percent but less than 20 percent, replace the connectors and backshells within 30 days after the detailed inspection. (iii) If the total backshell surface area corrosion is 20 percent or more, replace the connectors and backshells before further flight.

This AD was prompted by reports of significant corrosion of electrical connectors located in the main landing gear (MLG) wheel well. The FAA is issuing this AD to address corrosion and subsequent moisture ingress that may lead to electrical shorting of the connectors and incorrect functioning of critical systems necessary for safe flight and landing.

None.