# SDR 2026FA0000290

- Type: Service difficulty report (as reported; unverified)
- Difficulty date: April 23, 2026
- Submitted: April 24, 2026
- Operation: General aviation
- Aircraft: N9520
- Make and model: Cessna 172R
- Registry model: [Cessna 172R](https://openairdocs.org/model/cessna-172r) (OpenAirDocs)
- Aircraft serial: 17280385
- Engine: Lyc IO360L2A
- Engine time: 4,021 hours
- System (JASC): [8530 · Reciprocating Engine Cylinder Section](https://openairdocs.org/jasc/8530)
- Part: Button
- Part number: SL12892
- Part serial: 250923000028574
- Condition: Melted
- Location: Cylinders
- Part time: 38 hours
- Stage of operation: IN
- How discovered: V
- Nature of condition: M, J
- Precautionary procedure: K
- FAA source: FAA Service Difficulty Reporting System (https://sdrs.faa.gov/)
- Page: https://openairdocs.org/sdr/2026FA0000290

## Discrepancy

UPON INSPECTION AFTER MAJOR ENGINE OVERHAUL, IT WAS DISCOVERED THAT THE ROCKER SHAFT THRUST BUTTONS HAD EITHER PARTIALLY OR COMPLETELY MELTED. A COMPLETE ENGINE TEARDOWN INSPECTION WAS THEN PERFORMED, ONLY ONE CYLINDER HAD BOTH THRUST BUTTONS COMPLETELY INTACT. MELTED PLASTIC DEBRIS WAS DISCOVERED IN THE ROCKER COVERS, OIL SUMP SCREEN, OIL GALLERIES, AND OIL PUMP. THEN ENGINE HAS ONLY 37.8 HOURS SMOH, THIS FAILURE POSES A SEVERE RISK TO FLIGHT SAFETY. INFORMATION THAT WE RECEIVED STATED THAT FAULTY THRUST BUTTONS WILL FLOAT IN WATER AND GOOD PARTS WILL SINK. WE PERFORMED THIS TEST ON EVERY LOT NUMBER IN OUR INVENTORY AND FOUND SEVERAL LOT NUMBER BATCHES THAT FLOAT. WE THEN CONTACTED ANY CUSTOMERS WITH THE SUSPECT LOT NUMBER THRUST BUTTONS INSTALLED IN THEIR ENGINES TO INFORM THEM OF OUR FINDINGS AND TO REMOVE THE PARTS FROM SERVICE. SUSPECT LOT NUMBERS IN OUR INVENTORY WERE QUARANTINED.

---
OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.