FAA-2026-8803: proposed borescope inspections of the CFM56 HPT front seal

Item	Detail
Status	Proposed rule (NPRM), not yet in force
Docket	FAA-2026-8803
Project identifier	AD-2026-00385-E
Citation	91 FR 58042
Comments due	October 29, 2026
Engines on US-registered aircraft	39, by the FAA's estimate

Why the FAA proposed it

The manufacturer reported multiple cases of honeycomb separating from the surface of HPT inner stationary seals. Its investigation found that the affected seals may not have gone through the correct braze repair process.

Missing honeycomb can make the HPT forward outer seal vibrate, and that vibration can start cracks in the seal teeth that spread radially. Left unaddressed, the FAA says this could result in uncontained part release and damage to the engine and the airplane.

Which engines it covers

CFM56-5B, CFM56-5C and CFM56-7B engines with HPT inner stationary seal part number 1808M56G01 and a serial number listed in Table 3 of the matching CFM service bulletin:

Engine	Service bulletin listing the affected seals
CFM56-5B	CFM56-5B S/B 72-1125, Revision 02
CFM56-5C	CFM56-5C S/B 72-0811, Revision 02
CFM56-7B	CFM56-7B S/B 72-1093, Revision 02

The proposal lists the individual engine models in its applicability table. An engine without an affected seal isn't covered.

What it would require

1. Repetitive borescope inspections of the rotating air HPT front seal for cracks and other damage, following CFM S/B 72-1129 Revision 01 (-5B), 72-0813 Revision 01 (-5C) or 72-1096 Revision 01 (-7B).
2. If any crack is found, replacement of the rotating air HPT front seal before further flight.
3. At the next engine shop visit, removal and replacement of the affected HPT inner stationary seal, and an inspection of the removed seal for honeycomb separation.
4. If separation is found, replacement before further flight of the rotating air HPT front seal, the HPT rotor blades and the No. 3 ball bearing.

Completing steps 3 and 4 ends the repetitive inspections.

When the inspections would be due

Counted from the date the final AD takes effect:

Group	Engines	First BSI within	Then at intervals not exceeding
1	CFM56-5B listed in Table 1 of S/B 72-1129 R01	400 flight cycles	800 flight cycles
2	CFM56-5B listed in Table 2 of S/B 72-1129 R01	300 flight cycles	800 flight cycles
3	CFM56-5C listed in Table 1 of S/B 72-0813 R01	125 flight cycles	250 flight cycles
4	CFM56-7B listed in Table 1 of S/B 72-1096 R01	400 flight cycles	800 flight cycles
5	CFM56-7B listed in Table 2 of S/B 72-1096 R01	300 flight cycles	800 flight cycles

The groups also depend on the HPT front seal part number installed; the proposal's definitions give the exact criteria.

Credit for earlier work: an initial BSI already done using the July 2025 Revision 00 bulletins can count as the first inspection, and seal work done under earlier bulletin revisions can count toward steps 3 and 4.

What it would cost

The FAA's estimates, at $85 per work-hour:

Action	Labor	Parts	Per engine
BSI of the rotating air HPT front seal	8 hours, $680	$0	$680
Replace the HPT inner stationary seal	8 hours, $680	$173,700	$174,380
Inspect the removed seal	8 hours, $680	$0	$680
If needed: replace the rotating air HPT front seal	8 hours, $680	$601,400	$602,080
If needed: replace the HPT rotor blade set	8 hours, $680	$2,019,320	$2,020,000
If needed: replace the No. 3 ball bearing	8 hours, $680	$70,460	$71,140

Across 39 US engines, that puts one round of inspections at $26,520 and the seal replacements at $6,800,820. Real costs depend on access, travel, findings and your contracts.

What to do now

• Check whether any of your engines have HPT inner stationary seal P/N 1808M56G01 with a serial number in the bulletin tables.
• Get the referenced CFM service bulletins through CFM fleet support.
• If you've already done the BSI using the Revision 00 bulletins, keep those records.
• Plan inspection capacity: Group 3 engines would need their first check within 125 cycles of the effective date.
• Comment through the docket by October 29, 2026, and watch for the final rule, which can change thresholds, intervals and costs.

To comment, use regulations.gov and start with "Docket No. FAA-2026-8803; Project Identifier AD-2026-00385-E".

Where AirCheck fits

AirCheck records each borescope finding with its images, measurement and the manual reference it was checked against, and your inspector signs the report. Need an inspection team? Tell us the engine and where it is.

This page summarizes a proposed rule for planning. It isn't legal or compliance advice; work to the final AD and the current CFM service bulletins.