Document ID: chunk:federal_register_of_legislation:F2006B08589:body:0:p2
Version: federal_register_of_legislation:F2006B08589
Segment Type: other
Provision Reference: 
Character Range: 2962–4543

Requirement 1 checks.

               3.    a. If there have been previous reports of HSTA overspeed annunciation, then within 50 flight cycles after 31 March 1995, or

               3. b. Within 50 flight cycles following a reported incident of HSTA overspeed annunciation after 31 March 1995.

           Note: If either the HSTA or the Horizontal Stabilizer Trim Control Unit (HSTCU) was replaced in accordance with Requirements 2 or 3 then the Requirement 1 operational check is only required every 100 hours time in service unless another overspeed annunciation occurs.

 Background: There have been several reported instances of HSTA overspeed conditions.
           Investigation by Canadair has indicated that, in these cases, the no-back device on the HSTA (a design feature to prevent uncommanded movement of the HSTA screw jack when air loads are applied on the horizontal stabilizer) may have slipped (become reversible), resulting in overspeed annunciation. Each time this condition occurred, the HSTA mechanical brake prevented a HSTA runaway. Further in-depth investigation has identified some internal degraded conditions that may exist in the no-back device which could adversely affect the irreversibility, especially at low temperature and under high air loads. The actions required by this Directive are designed to assist in the early detection of defective HSTA or HSTCU components.
           Flight Manual Amendments A/600-1A11/17, A/600-2A12/36, A/600-2B16/22 and A/600-2B16H/24 are complementary to this Directive, providing additional advice to aircrew.