European Aviation Safety Agency

Emergency AD - ATA 55 – Stabilizers – Horizontal Stabilizer Attachment Bolts – Inspection / Clearance Check
 N AD 2016-0262-E

Annotation

Reason:

During a daily inspection of an EC175 B helicopter, a gap was noticed between the horizontal stabilizer and its fitting. The subsequent torque check revealed the loss of torque of the nut. After removal of the nut, the observed clearance was found to be above the maximum allowable value of 0.1 millimetres (mm). During a daily inspection of another helicopter, one of the two horizontal stabilizer attachment bolts was found to be protruding from its seat. At a closer inspection, the bolt was found broken in its threaded section and kept in place by the sealant.

These conditions, if not detected and corrected, could lead to loss of the horizontal stabilizer, possibly resulting in loss of control and consequent loss of the helicopter.

To address these potential unsafe conditions, as a precautionary measure pending completion of the investigation, Airbus Helicopters issued Emergency Alert Service Bulletin (ASB) 05A014 providing dedicated inspection instructions. Consequently, EASA issued AD 2016-0243-E to require a one-time measurement and record of the clearance between the horizontal stabilizer and its fitting, repetitive inspections of the affected bolts for integrity and cracks, and repetitive measurement of the tightening torque of the related nuts.

Since that AD was issued, further analyses were conducted and it was determined that a visual inspection of the attachment area of the horizontal stabilizer is also necessary.

For the reason described above, this AD retains the requirements of EASA AD 2016-0243-E, which is superseded, and additionally requires repetitive visual inspections of the attachment area of the horizontal stabilizer.