CRJ-900 aircraft inspector reported after inspecting the work of the avionics technicians they gave the ok to close the floorboard. The aircraft experienced several caution warnings on take-off due to the AHRS computer not being secured in the rack.

Narrative

On take off; Aircraft X experienced wind shear; pitch; roll; and stall caution warnings that were traced back to the AHRS Computer being unsecured in its rack. Discovered in ZZZ; made aware by Person A after he was contacted by ZZZ.Cause: My understanding is an avionics tech from Company X released the locking lugs from the AHRS computer to allow for slack in the harness to facilitate installation of two splices and diodes in that wiring harness. Company X was two Interior installers short that day and two of the three Avionics techs were required to fill in as interior installers to maintain the schedule. Inspection of the aft avionics bay is required twice during the WiFi Mod. First; the main harness that is routed aft through most of the aft avionics bay along the upper LH corner of the bay. This routes it directly over the top of the AHRS computer which is located most of the way aft and on the LH side and is not readily visible. This inspection step is accomplished before the wire splicing which is the next Inspection step. This step is an inspection of the area of the harness that is disturbed for splicing and installation of the diodes which is located on the opposite side of the aft avionics bay at the bottom; underneath the floorboard. the Inspector lifts up the unsecured floorboard to gain visual access of the modification and then gives the ok" to close the floorboard. It is dark in there and a flashlight is used and with the floorboard lifted up; the AHRS computer cannot be seen and since the releasing of the AHRS computer is not in the procedure; it is not typically looked at. It was discussed among ZZZ maintenance as to how it happened and how it was overlooked and how could it be prevented in the future.Suggestions: Because the wiring harness does tend to be difficult to splice without slack allowed; the releasing of the AHRS computer should be a step added to the procedures that will cover the inspection requirements that will ensure that the AHRS computer will be properly secured at the time of release."