Eurocopter AS 350/355/EC130 - Astar/Twinstar/Ecureuil
Situational Awareness; Time Pressure; Workload
Deviation / Discrepancy - Procedural Published Material / Policy
Incorrect / Not Installed / Unavailable Part; Procedure
During a complete teardown of an Arriel 2B1 to replace the MO1 Module due to being out of tolerance after inspected in accordance with a Service Bulletin (SB). The tooling used to remove and replace the MO5 Module required that three bolts be removed from the casings that the tool may be fitted to the MO5 Module. Upon rebuild of the engine I had gone over several times to make sure canon plugs were in the correct spots (they can be installed in the wrong place). Making also certain that all fittings where torqued down. The missing bolts while the MO5 Module is installed are hidden under the exhaust. Even with repeated checks these bolts were overlooked. Though that lack of these bolts would not have caused a severe failure; the fact that they were missing is not acceptable.I suggest that each person involved in the project; at each step to complete the task look over and ensure procedures are being followed and all work is checked. Checklists made to ensure that each items is accounted for. We are having a safety meeting with 3 mechanics as of today and will have another meeting when we have all mechanics available so that we all can make it clear on how serious of an issue this is.
When replacing an MO1 Module on an Arriel 2B1 Helicopter Engine; three bolts are removed from the MO5 Module casing to accommodate the tooling. These bolts were left off when the engine was installed.