Date: 202110
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Night
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Engine Borescope Plug
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Powerplant; Maintenance Airframe
Human factors: Troubleshooting; Human-Machine Interface; Communication Breakdown; Situational Awareness
Second reporter function: Technician
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
When detected: Routine Inspection
Result: General Maintenance Action
Contributing factors: Aircraft; Procedure
Primary problem: Procedure

Narrative: This happened in an overnight at ZZZ on Aircraft X during a borescope inspection on #2 ENG where second shift began the job card and removed the borescope ports. Technician Y and I came in on 3rd shift and after inspections cleared the engine heat level to borescope it around XA00 on DATE 2; we finished the borescope inspection. We installed all the borescope and igniters which we found bagged and tagged which made it easy to see; but we missed 1 that wasn't bagged and easy to see nearly eye level because it wasn't bagged or tagged.The event occurred because we ourselves did not remove the plugs. We made the mistake of paying attention to the ports that were bagged and removed and failed to verify exactly what ports were removed by the previous shift. The missing plug was nearly eye level @ the 10 O'clock position; but since it was not clearly bagged or tagged we failed to install it. I was unfamiliar with the Job Card and made the mistake of assuming only the bagged hardware was removed.I think the best suggestion I can make would be to put in Job Card to attach streamers that could be easily seen on the hardware or near the plug holes while doing the borescope inspection. Had we seen the hardware or plug hole clearly bagged or streamed this would have never happened. I also think that a better overlap between shifts would also have never allowed something like this to happen. If we had a better overlap between shifts at the aircraft things like this would be greatly reduced.


Second narrative: We were issued Aircraft X on third shift on DATE 1 borescope # 2 engine inspection was started by second shift. We received the job card and borescope ports were already removed. Inspection said engine was hot and entered with device around XA00 DATE 2. All the plugs were in bags and were put back from where they came from except 1. One plug was missed and not seen; no bag around the open port was seen; no tape; no bag; this port was missed. Every port open had a bagThis incident happened because we didn't remove any of the plugs ourselves; we put back the hardware that were in bags but the mistake we made was not to verify what plugs were removed by second shift. The plug missing was not bagged taped or marked; this plug was not installed. I was unfamiliar with the job card and made the mistake of assuming only the plugs in the bags were removedI think tape should be used or blank plugs with streamers to put in or on the engine case. Streamers that are long and easy to see. More effective turnovers with what was done and where parts are. This would have never happened if better communication was used.


Synopsis: Technicians reported an engine borescope plug was left uninstalled and was discovered post maintenance.