Caravan 208B
Maintenance Airframe; Maintenance Powerplant; Maintenance Inspection Authority
Situational Awareness
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Aircraft; Human Factors
A Cessna 208B type aircraft was in the Maintenance hangar undergoing troubleshooting for faulty fuel flow indications. The indicator proper did not fix the issue; so we had discussed re indexing the transmitter to obtain a smoother reading. The work performed required us to open the RH upper cowl.  Having re indexed the transmitter; performed a successful run and leak check; the mechanic performing the work then applied safety wire to the transmitter per the [manual]. This is a [inspection] item; and I performed the visual post maintenance inspection on the transmitter. I closed the cowl; but do not recall latching it. The airplane was then released for a check flight. An hour or so later a pilot arrived to perform the check flight. Being aware that the flight was for the transmitter maintenance; he took off. Upon take off; the RH cowl door came open and remained open for the rest of the flight.  An emergency was not declared; and the pilot landed safely. I came back up to the hangar to inspect the plane and speak with the pilot.  The pilot then informed me he had performed a satisfactory preflight; and had checked the cowls secure. The damage to the aircraft is negligible; with small amounts of paint exchanged. No damage to the RH upper cowl was noted. The aircraft was returned to service.I was informed by telephone after the pilot had returned from the check flight. The pilot had reported it to the lead night shift mechanic; who then reported it to me.  The event occurred most likely due to distractions on my part. As [the] inspector; I was the last person to visually inspect the aircraft out of maintenance.  I did not verify the latches locked on the cowl after inspecting the work performed.  The aircraft was brought into the hangar and [maintenance control] informed.  I then sought out the pilot to get the details of the flight.  The aircraft was then inspected visually for damage.  Only slight; negligible damage was noted; and the aircraft was then released for service.  I was focused on too many tasks to properly carry out the duty of [the] inspector.  I had become distracted by other tasks on hand; and should have delegated the [inspector] to another mechanic.
After performing maintenance on this airplane; the Maintenance personal neglected to properly latch the Right Hand upper cowl.