| NPRM | AOPA Comment | Final Rule |
| Removal of Exhaust System for detailed inspection and material determination. Different compliance schedules for stainless steel and Inconel systems. | Inconel is not necessarily the material of choice. Stainless steel and Inconel systems should be held to the same compliance schedules. Material determination is not necessary. | Identical compliance schedules for Inconel and stainless steel exhaust systems, no material determination requirements. |
| Inspection of exhaust system, within next 2 years, by one of three FAA specified exhaust repair stations | Mandatory exhaust system inspections by one of three FAA designated repair stations cannot be accomplished in the proposed two-year compliance period. | Exhaust systems can be inspected and/or repaired by any FAA-approved exhaust repair station. |
| Removal of slip joints for replacement at 500 hours/TIS | Repetitive removal of the slip joints may damage or otherwise impair exhaust system integrity. | Inspect slip joints for freedom of movement. Removal of slip joints required only at 2500 hour/TIS intervals. |
| Pressure tests to determine exhaust system integrity required only for stainless steel or mixed exhaust systems. | Repetitive visual inspections and pressure tests are currently providing an adequate level of safety. Pressure tests should be used for all exhaust systems regardless of the material they're made of. | Pressure test and visually inspect the exhaust system upon the accumulation of 5 years since installing a new or overhauled exhaust system or within the next 100 hours/TIS, whichever occurs later. |
| Compliance schedule not in concert with regularly scheduled aircraft maintenance. | AD compliance actions should be coordinated with regularly scheduled aircraft maintenance. | Compliance times synchronized with regularly scheduled aircraft maintenance such as annual inspections and engine overhaul. |
| Minimum acceptable wall thickness of exhaust system components of 0.25in. | Proposed minimum exhaust system component wall thickness is unneeded and inappropriate. | No requirement to inspect for minimum wall thickness. |
| Visual Inspection within the next 100 hours/TIS for Inconel or 50 hours/TIS for stainless steel systems | Inconel is not necessarily the material of choice. Stainless steel and Inconel systems should be held to the same compliance schedules. Material determination is not necessary. | Visual Inspection of Inconel and stainless steel systems required within the next 50 hours TIS or next 30 days whichever occurs later. |