CE-680A Maintenance Technician reported non-compliance with SOPs affecting landing gear extend/retract system made during previous maintenance visit.

Narrative

Person B and I were assigned to Aircraft X under [our] Work Card. The crew noted two issues in their single discrepancy. Issue 1: GEAR DISAGREE L R N; all 3 gears would not extend. Issue 2: When attempting to use the Emergency Gear Extension System; it was inoperative due to the pull knob being stuck. We inspected the Emergency Gear Extension Pneumatic Bottle and Control Cable. We found that the bottle control arm was improperly safetied; an unsuitable safety wire was used; and the Use Copper Wire p/n: MS20995CY15 or equivalent' Placard was improperly installed into a position that impeded the operation of the control cable. We took pictures and notified maintenance control and maintenance control supervisors of our findings. Had the crew not been able to get the landing gears extended by pulling the Emergency Release Handles/Cables; the aircraft would've suffered a full gear up landing. The GEAR DISAGREE L R N was caused by the failure of the Landing Gear Control Handle Assembly which the extend command was not being sent to the Landing Gear Control PCB (Printed Circuit Board). Per a history search; the Pneumatic Bottle was last serviced on day 0 under [the] Work Card.Suggestions: A special placard is installed with the Emergency Gear Extension Pneumatic Bottle to ensure a specific safety wire is used. Technicians must adhere to this placard. CE680A MM 32-34-35 Figure 401 : Sheet 1 : Detail A depicts the proper routing of the safety wire for the control arm. This Figure must be referenced when installing the control arm safety wire. And the placard must be installed onto the bottle in a way that does not impede the control cable operation."