SAIB NM-11-52

FAA Aviation Safety

SPECIAL AIRWORTHINESS

INFORMATION BULLETIN SAIB: NM-11-52 SUBJ: Flight Controls: Stabilizer Control System Date: August 31, 2011 This is information only. Recommendations aren’t mandatory.

Introduction

This Special Airworthiness Information Bulletin advises registered owners and operators of Bombardier, Inc. Model DHC-8-400 series airplanes of erroneous activation of the take-off configuration aural warning, which resulted in aborted take-offs due to the elevator trim being selected to the maximum of the acceptable take-off trim band range.

Background

Several incidents have occurred of erroneous take-off configuration warnings which resulted in aborted take-offs due to the elevator trim being selected to the maximum of the acceptable take-off trim band range. Investigation revealed that if the elevator trim is set at either end of the elevator trim take-off band due to built-in tolerances of the Flight Control Electronic Control Unit (FCECU), the elevator trim indicator system could detect that the trim is out of range and trigger the aural take-off warning, resulting in an increased number of aborted take-offs. Bombardier, Inc. has issued service information to provide operators with guidelines for modifying the FCECU to reduce aborted take-offs by expanding the take-off warning signal range.

At this time, the airworthiness concern is not an unsafe condition that would warrant airworthiness directive (AD) action under Title 14 of the Code of Federal Aviation Regulations (14 CFR) part 39.

Recommendations

The FAA strongly recommends that all owners and operators of the Bom bardier airplanes identified above comply with the actions outlined in Bombardier Inc. Service Bulletin 84-27-54, Revision A, dated February 25, 2011, at the earliest opportunity.

For Further Information Contact

Cesar A. Gomez, Aerospace Engineer, Airframe and Mechanical Systems Branch, ANE-171, FAA, New York Aircraft Certification Office, 1600 Stewart Avenue, Suite 410, Westbury, New York 11590; phone: (516) 228-7318; fax: (516) 794-5531; email: cesar.gomez@faa.gov.

For Related Service Information Contact

Bombardier, Inc., Aerospace Commercial Aircraft, telephone 416-375-4076; fax 416-375-4539;

e-mail syed.rizvi@aero.bombardier.com; Internet http://www.bombardier.com.