Safety Recommendations A-06-24 through -26

The National Transportation Safety Board recommends the following to the Federal Aviation Administration:

Require MD Helicopters, Inc. (MDHI), to conduct additional tests to enable the full analysis of all critical load cases for tension-torsion straps installed in the anti-torque fan of MDHI model 500N series, 600N, and MD900 helicopters, including load cases that create regions of transverse shear or compression in the fiber-reinforced areas of the straps. (A-06-24)

Based on existing data and additional data acquired during accomplishment of recommendation A-06-24, take regulatory action as appropriate to require changes in the inspection and replacement of tension-torsion straps installed in anti-torque fans of MD Helicopters, Inc., model 500N series, 600N, and MD900 helicopters. (A-06-25)

During the non-destructive inspections of tension-torsion (T-T) straps installed in anti-torque fans in MD Helicopters, Inc., model MD900 helicopters and any other models requiring x-ray inspections, require that the x-ray film be examined for indications of both progressive fiber fractures and for longitudinal cracks in the T-T straps, and require that any T-T straps in which progressive fiber fractures or longitudinal cracks are found be removed from service. (A-06-26)

FMI: www.ntsb.gov/recs/letters/2006/A06_24_26.pdf