Operators may recall the original AD 2016-13-09 where a determination was made that certain maintenance tasks for the Horizontal Stabilizer Trim Actuator (HSTA) were inadequate. The AD was originally issued to detect and correct premature wear and cracking of the HSTA, which could result in the failure of the HSTA and consequent loss of control of the aircraft.

While Bombardier worked with suppliers in an attempt to build-up a rotable pool, currently there is a limited quantity of HSTAs to support the restoration or to complete the special detailed inspection tasks.

Due to the CMR task 27-42-01-110** introduction, there is an expected increase in the rate of HSTA removals and shipments to the supplier between 2022 and 2027, with an anticipated peak in late 2024 and early 2025.  Put simply, there is a shortage of overhauled HSTAs available to meet immediate high demand.

The good news for operators is that as of July 15, 2024, an AMOC for this issue was approved. Operators now have an additional 2 years to comply with the overhaul of the HSTA.

As per FAA guidance, Bombardier applied for and received approval of a global AMOC (Ref 1.11) against Airworthiness Directive 2016-13-09 (Ref 1.7) for all Challenger 604/605/650 aircraft models, to allow US-registered operators to comply with paragraph (g) of the FAA AD 2016-13-09 by revising the maintenance program to incorporate the following CMR tasks at the intervals published in the applicable TLMC/AWL revisions identified in Table 1 of TCCA AD CF-2024-16:

CMR Task 27-42-01-109* (Restoration [Overhaul] of the Horizontal Stabilizer Trim Actuator, Part No. 604-92305-7 and Subs [Vendor Part No. 8454-3 and Subs]); and

CMR Task 27-42-01-111* (Detailed Inspection of the Horizontal Trim Actuator [HSTA] Secondary Load Path Indicator, Part No. 604-92305-7 and Subs [Vendor Part No. 8454-3 and Subs]); and

CMR Task 27-42-01-110** (Special Detailed Inspection of the Horizontal Stabilizer Trim Actuator [HSTA], p/n: 604−92305−7 and Subs). NOTE: The interval can take credit for the phase-in in Note 2 of TCCA AD CF-2024-16.