Airworthiness Directives; Bombardier Inc. Model Otter DHC-3 Airplanes

The FAA is revising Airworthiness Directive (AD) 2004-05-01, which applies to certain Bombardier Inc. (formerly deHavilland Inc.) Model Otter DHC-3 airplanes that have turbine engines installed per one of three supplemental type certificates (STC). AD 2004-05-01 currently prohibits you from operating any affected airplane with these engine and propeller configurations unless a new STC for an elevator servo-tab with a redundant control linkage is installed. The FAA has since evaluated concerns, comments, and technical information related to all three STC configurations. Based on that evaluation, we have determined that further evaluation is necessary for the STCs owned by Texas Turbines Conversions, Inc., and Canada Turbine Conversions, Inc. Therefore, we are removing reference to these STCs from the AD, and the AD will only apply to those Bombardier Inc. airplanes that incorporate STC No. SA3777NM (A.M. Luton installation of Pratt and Whitney PT6A-34/ -135 engine). After further evaluation, we may initiate rulemaking action regarding airplanes with the Texas Turbines Conversions, Inc., and Canada Turbine Conversions, Inc., STC configurations.