A Line Mechanic reports the Stall Warning System Maintenance procedures Operational Checks for their DHC-Q400 aircraft; did not include a CAT-3 Landing Operational Test requirement whenever a Stall Protection Module (SPM) circuit breakers had popped. The SPM circuit breakers were part of their CAT-3 Landing Minimums Manuals.
Synopsis
A Line Mechanic reports the Stall Warning System Maintenance procedures Operational Checks for their DHC-Q400 aircraft; did not include a CAT-3 Landing Operational Test requirement whenever a Stall Protection Module (SPM) circuit breakers had popped. The SPM circuit breakers were part of their CAT-3 Landing Minimums Manuals.
Narrative
I was called out to gate for a DHC-Q400 aircraft returning to gate December 2011 at approximately XA:00 am for Stall System Fail # 1; # 2; Caution illuminated and Stall Protection Module-1 (SPM-1) and SPM-2 circuit breakers popped. I reset the circuit breakers in accordance with General Procedures Manual (GPM) and complied with the Operational Check of Stall Warning System in accordance with Aircraft Maintenance Manual (AMM) Task 27-33-00- 710; operations checks good after test. I was notified the following day from a Lead Technician [there was an issue].The Operational Check of the Stall Warning System in accordance with AMM Task 27-33-00-710 did not reference the Lower Level Minimums (LLM) sensitive components associated with this task. The AMM Task 27-33-00-710 now contains a company [Maintenance Engineering] Supplement with a revision date of December 2011; to comply with a Maintenance Task Card (MTC) # XXX and LLM return to service [requirements]. I verified with Maintenance Control that the aircraft was in compliance and MTC # XXX had been complied with [and noted] in the logbook. Suggest inserting Company [Engineering] Supplements on every AMM Task associated with LLM sensitive components. Should have recognized the relationship of the circuit breakers associated to LLM components with Stick Shaker System.
NASA callback
Reporter stated the lack of adequate information in their manuals about additional tests being required prior to returning a Q400 back to service; started with a pilot trying to do a Stick Shaker Preflight Test that did not respond. Q400 aircraft have a lot of computer glitches and they are often signed-off by just resetting computers and circuit breakers. The standard procedure was to reset the Stall Warning System's Stall Protection Modules (SPM-1) and (SPM-2) circuit breakers and perform an SPM Test. No one was aware the circuit breakers for the SPMs were also associated with the CAT-3 Landing System and part of the Landing Minimums Manual that included the Heads-Up Guidance System (HGS) and required a CAT-3 Check to maintain CAT-3 Landing status; whenever an SPM circuit Breaker had popped. Their manuals have since been crossed-referenced and revised to address that issue.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.