FAA Orders Jet Engine Honeycomb Inspections for Cracks
Published Date: 9/14/2026
Proposed Rule
Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain CFM International, S.A. (CFM) Model CFM56-5B, CFM56-5C, and CFM56-7B engines with a certain high-pressure turbine (HPT) inner stationary seal installed. This proposed AD was prompted by multiple reports of honeycomb separation from the surface of HPT inner stationary seals. This proposed AD would require initial and repetitive borescope inspections (BSIs) of the rotating air HPT front seal for cracks and, depending on the results, replacement with a part eligible for installation. This proposed AD would also require removal and replacement of the affected HPT inner stationary seal. This proposed AD would also require inspection of the affected HPT inner stationary seal for honeycomb separation and, depending on the results of the inspection, removal and replacement of the rotating air HPT front seal, HPT rotor blades, and No. 3 ball bearing. The FAA is proposing this AD to address the unsafe condition on these products.
Analyzed Economic Effects
3 provisions identified: 0 benefits, 3 costs, 0 mixed.
Mandatory seal replacement at shop visit
At the next engine shop visit after the AD becomes effective, you must remove and replace the affected HPT inner stationary seal (P/N 1808M56G01). The FAA estimates replacement per engine costs at $680 labor plus $173,700 parts = $174,380, and estimates 39 U.S.-registered engines would total $6,800,820.
Large on-condition replacement costs if damage found
If cracks or honeycomb separation are found, you must replace components before further flight. The NPRM lists on-condition estimated costs per engine: rotating air HPT front seal about $602,080 total, HPT rotor blades (set) about $2,020,000 total, and No. 3 ball bearing about $71,140 total.
Mandatory repetitive borescope inspections
If you operate airplanes with the listed CFM56-5B/5C/7B engines, you must perform initial and repeating borescope inspections (BSIs) of the rotating air HPT front seal. The NPRM sets specific intervals by group: Group 1 — within 400 flight cycles (FCs) then every 800 FCs; Group 2 — within 300 FCs then every 800 FCs; Group 3 — within 125 FCs then every 250 FCs; Group 4 — within 400 FCs then every 800 FCs; Group 5 — within 300 FCs then every 800 FCs.
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