Comment from Air China Engineering Division

The Air China Engineering Division submits the following comments regarding the Notice of Proposed Rulemaking (NPRM) for the above-referenced Airworthiness Directive (AD). While we acknowledge the safety hazard identified by the FAA, we consider that the proposed compliance method — replacement of affected main fuel pumps at the next engine shop visit — may fail to adequately resolve the unsafe condition in a timely manner. Our concerns stem from two key operational and technical considerations: 1. Operational Bypass Risk Resulting from Line Replaceable Unit Rotation The main fuel pump is a high-utilization Line Replaceable Unit (LRU) in fleet daily operations. The proposed compliance requirement of "replacement at the next engine shop visit" creates a critical operational loophole. Operators may remove serviceable but AD-affected main fuel pumps from engines prior to scheduled shop visits, fit engines with unserviceable, repair-required pumps for shop dispatch, and reinstall the original affected pumps on other in-service engines. This LRU rotation practice allows affected fuel pumps to remain in active fleet service indefinitely, directly circumventing the safety mitigation intent of the proposed AD. Notably, the current proposal contains no preventive safeguards against such operational workarounds, potentially delaying hazard remediation by thousands of flight cycles. 2. Unsubstantiated Reliability Assumption for Components Pending Shop Visits The proposed AD presumes that all affected main fuel pumps can operate reliably without failure until the next scheduled engine shop visit. For GEnx engines, the typical interval between engine shop visits exceeds 3,000 flight cycles. Given the low cycles since overhaul (CSO) of the main fuel pumps involved in the relevant unsafe event, there is insufficient technical basis to validate that these affected units can sustain extended safe operation without definitive time or cycle limitations. Recommended Modifications to the Proposed AD To eliminate the identified unsafe condition in a timely and definitive manner, Air China respectfully requests the FAA to amend the proposed AD to incorporate the following mandatory provisions: 1. Mandatory Flight Cycle Limit: Establish a maximum allowable flight cycle limit for all AD-affected main fuel pumps, effective either from the AD’s issuance date or based on their respective cycles since overhaul (CSO). All affected pumps shall be removed from active service immediately upon reaching the prescribed limit, regardless of the engine’s scheduled shop visit timeline. 2. Accelerated Replacement Support Requirement: Require the manufacturer to provide sufficient inventory of eligible replacement parts to support accelerated fleet-wide replacement, ensuring that safety-critical components are not kept in service due to spare parts shortages.