AD 2026-17-10: What Shops Signing Off Lycoming O-235, O-540, and IO-540 Engines Need to Know

If you're about to sign off a return-to-service on a Lycoming O-235, O-540, or IO-540 this month, read paragraph (g)(2) before you pick up the pen. AD 2026-17-10 doesn't just target a defective batch of piston pins — it reverses the burden of proof onto whoever is certifying the aircraft, and it did so without warning: the FAA invoked "good cause" under APA § 553(b) and (d) to make the rule effective immediately, taking public comment only after the fact. Absent an FAA Form 8130-3 showing the pin was made outside a suspect four-year window, the engine is unsafe by default.

What You're Actually Dealing With

Lycoming brought this to the FAA after multiple reports of metal particulates showing up during oil changes, plus two in-flight failures with no precursor symptoms.

The root cause is on the supply side: a pin vendor changed its honing and tooling process and began shipping thin-wall pins (P/N LW-13445) with microcracks and inclusions in the base-metal bore. Any pin manufactured between January 7, 2021, and December 15, 2025, is suspect regardless of total time or time since overhaul. A pin failure can wreak havoc in the engine: debris circulates rapidly, taking out bearings and cylinders and clogging oil passages en route, leading to oil starvation and an in-flight shutdown without warning.

The Paperwork Problem You're Now Certifying Against

Paragraph (c) and the definition in (g)(2) are the ones to read twice before you touch a logbook entry. The AD defines an "affected piston pin" as any P/N LW-13445 with an 8130-3 dated in the suspect window, or any pin where the production date can't be determined, or the 8130-3 no longer exists.

The AD makes the burden shift explicit: an affected piston pin includes any LW-13445 where the production date on the Form 8130-3 cannot be determined, or where the Form 8130-3 is not available. That's the regulatory basis for treating missing paperwork as an unsafe condition.

That last clause is the catch: you're not clearing a pin by showing it isn't affected — you're stuck proving a negative with a document the owner may have legally discarded years ago. If you can't produce it, you must treat the pin as affected. Don't sign off "inspected, no discrepancies noted" on the strength of a narrative logbook entry alone.

One detail worth knowing before you write the pin off as unprovable: paragraph (c) accepts an 8130-3 from the OEM for production, dated outside the suspect window. The definition points specifically to Lycoming's own production paperwork, not just whatever the owner has on file. If the original tag is missing, it's worth contacting Lycoming to see whether they can supply the 8130-3 from their production records before you assume the pin is a lost cause.

Lesson for Your Shop

14 CFR § 91.417(b)(1) sets a floor, not a ceiling. The one-year/superseded rule is the minimum retention period, not a recommendation, and an 8130-3 is a bad candidate for minimum retention. It can't be reconstructed once it's gone; it's the only document that proves where and when a part was made. Treat parts-conformity paperwork — 8130-3s, material certs, life-limited part records — as permanent records kept for the life of the part or the aircraft and transferred at sale. It costs nothing to keep, and as this AD shows, it can save an owner from a presumptive-unsafe finding years later.

Field Notes

1. Applicability & Scope

• Affected Models: Lycoming O-235, O-540, and IO-540 engines with serial numbers listed in Table 2 or Table 3 of Lycoming MSB 667A.
• Suspect Part: Thin-wall Piston Pin P/N LW-13445 (manufactured between Jan 7, 2021, and Dec 15, 2025).
• Inventory Control: Quarantine unused LW-13445 stock from the suspect date range immediately; only a "part eligible for installation" under (g)(1) may go into any engine.

2. Inspection & Replacement Thresholds

• Initial Oil/Screen Inspection: Within 5 hours TIS, unless already done in the last 10. This 5-hour inspection requirement does not appear in MSB 667A — it is stricter than the manufacturer's guidance.
• Table 3 High-Time Exception: Over 150 hours TIS on suspect pins, inspect before further flight.
• If Metal Debris Is Found: Replace the pin before further flight. No deferrals.
• If Oil Is Clean (Table 2 Engines): Defer to the next cylinder pull or overhaul, per SI 1009BE.
• If Oil Is Clean (Table 3, fewer than 150 hrs TIS): Replace within 25 hours TIS, or before 150 total hours on the pin.

3. Shop Floor & Sign-off Prerequisites

• Chase the Paperwork First: Pull original 8130-3s or logbook cylinder-work entries since 2021. No proof means the pin defaults to "affected," unless Lycoming can supply the 8130-3.
• Full Filter Cut (MSB 480): Cut the element open and check both screens. Partial checks don't satisfy the AD.
• SFP Sequencing: No SFP for the initial-inspection flight. An SFP is only available afterward, to ferry for pin replacement.
• Warranty Support: Check SSP-875 / MSB 667A allowances for parts, freight, and labor before billing owners out-of-pocket.

Industry Pushback: Why Operators & Maintenance Shops Are Calling Foul

The docket contains real technical pushback worth citing if you're filing comments or fielding owner questions, including a formal Global AMOC proposal filed on behalf of the Comanche Owners Community:

• The labor number is unrealistic. The FAA's economic analysis assumes 2 work-hours per engine for pin replacement, oil change, and screen inspections combined. That doesn't match reality: replacing pins on a 4- or 6-cylinder engine requires pulling every cylinder, reassembling, re-torquing, and performing test runs. Real shop estimates for a full top-end R&R run 20 to 30 labor hours per engine.
• It penalizes compliant recordkeeping. 14 CFR § 91.417(b)(1) lets Part 91 owners discard routine maintenance records and parts tags once superseded or after one year. This AD treats that same lawful record disposal as grounds to presume an engine is unsafe, even where § 43.9 logbook entries show unbroken maintenance history.
• Scope has gaps you may already be hitting. Some listed models, such as the Robinson Helicopter O-540-F1B5 and IO-540-AE1A5, spec heavy-wall pins (P/N LW-14078) in their parts catalogs and cannot legally carry the affected LW-13445 pin. Flag that before inspecting an engine that structurally cannot have the suspect part. Check the Engine Parts Catalog (PC) alongside MSB 667A before logging non-applicability. Separately, pre-2021 engines with no cylinder work since original assembly may be technically included based on missing paperwork.

As of this writing, the FAA hasn't responded to any of these comments; the docket stays open through October 13, 2026, so whether the agency amends the rule in response is still an open question.

Why There Was No Advance Comment Period

The FAA's stated rationale: microcracks aren't detectable before failure, and compliance windows this tight — "before further flight" or within 25 hours TIS — don't fit the standard rulemaking timeline. Comments remain open through October 13, 2026, useful context if an owner asks why they're seeing this AD with zero advance notice.

Why It Matters

The FAA estimates this AD affects 957 engines installed on airplanes of U.S. registry, at an official cost of $2,370 per engine based on 2 labor hours, which is how the agency gets to that $2.27 million fleet-wide figure. Realistic shop time runs into the thousands of dollars and up to 30 hours per aircraft — build that into your scheduling and owner conversations now.

Between the compressed timeline, the reversed burden of proof, and a paperwork standard that conflicts with Part 91 retention rules, this is an AD worth commenting on directly. The docket remains open through October 13, 2026.

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