Airworthiness Directives; Saab AB, Saab Aeronautics (Formerly Known as Saab AB, Saab Aerosystems) Airplanes

摘要

We propose to supersede Airworthiness Directive (AD) 2012-24- 06 for certain Saab AB, Saab Aeronautics (formerly known as Saab AB, Saab Aerosystems) Model 340A (SAAB/SF340A) and SAAB 340B airplanes. AD 2012-24-06 requires replacing the stall warning computer (SWC) with a new SWC, which provides an artificial stall warning in icing conditions, and modifying the airplane for the replacement of the SWC. Since we issued AD 2012-24-06, a determination was made that airplanes with certain modifications were excluded from the AD applicability and are affected by the identified unsafe condition and the SWC required by AD 2012-24-06 contained erroneous logic. This proposed AD would add airplanes to the applicability, and would add requirements to replace the existing SWCs with new, improved SWCs and modify the airplane for the new replacement of the SWC. We are proposing this AD to prevent natural stall events during operation in icing conditions, which could result in loss of control of the airplane.