Model 414; STC SA2680SW (400 Horsepower Engine Conversion)

Model 414; STC SA2680SW (400 Horsepower Engine Conversion)

The FAA Small Airplane Directorate, Continued Operational Safety (ACE-113) located in Kansas City, Missouri, provided the following article. (The article is published as it was received from ACE-113.)

STC SA2680SW modifies the Cessna 414 airplane by the installation of larger engines and different propellers. The STC replaces the factory installed 310 horsepower TCM TSIO 520-() engines and three-bladed propellers with 400 horsepower Textron-Lycoming IO 720-() engines, that are turbo-normalized, and four-bladed Hartzell propellers. The installation includes an overboost safety protection system designed to limit manifold pressure of the turbo-normalized system to that of sea level at all altitudes up to the system critical altitude.

If the safety protection system is not properly installed and functioning, a manifold overboost condition can occur creating excessive manifold pressures to be generated that may exceed the design specifications and may lead to failure of engine cylinder assemblies, crankshaft, and/or engine crankcase.

Operators should have a properly FAA-certified mechanic inspect any Cessna 414 with STC SA2680SW installed for proper installation and operation of the engine overboost redundant safety protection system. Aircraft may be returned to service after inspection has determined installation is in an airworthy condition.

System components include:
   Turbocharger    Garrett Model TE0659
    Garrett P/N 406610-27

   Pressure Relief Valve (31 in. Hg)    Garrett P/N 470944-16 (old p/n)
    Garrett P/N 470944-25 (new p/n)

   Variable Absolute Pressure Controller    Garrett P/N 470836-1

   Wastegate Valve     Garrett P/N 481036-1

Garrett-Airesearch Aerospace is now Kelly Aerospace, Montgomery, Alabama.
Flightcrews should be advised that less than cautious operation of throttles could result in an overboost condition on engines that do not have a properly functioning overboost protection system.

Monitoring of manifold pressure indicators during throttle advances will provide an indication of a system that is not operating properly per design specifications (reference STC SA2680SW Aircraft Flight Manual supplement for manifold pressure limits). Manual limiting of manifold pressure by throttle position can prevent an overboost condition in the event of inadequate overboost protection.

Flight crews should report any overboost condition immediately and have a properly FAA certified mechanic resolve all defective conditions before further flight.

The FAA is preparing a Special Airworthiness Information Bulletin (SAIB) to notify owner/operators of Cessna 414 aircraft with STC SA2680SW installed of this safety condition.

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