Regulatory Brief -- FAA issues long-awaited twin Cessna exhaust AD

Preliminary Twin Cessna Exhaust AD Compliance Comparison � January 20, 2000

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.