Narrative:

Aircraft X; a eurocopter ec-135 was placed into maintenance for its 800-hour inspections. While complying with the aircraft inspections; the A-2411 datasheet [indicated] a 1600-hour inspection was due. The main rotor hub and the main rotor hub shaft were removed in accordance with ec-135 maintenance manual chapter 62-31-00 (4-3); removal main rotor hub-shaft; with no incident. We then carried out the inspection of the spacer tube. Upon reassembly of main rotor hub-shaft in accordance with ec-135 MM chapter 62-31-00 (4-4); the bolts that attach the hinged support to the bearing block just aft of the mixing unit of this aircraft were installed. While installing the main rotor hub; I was on the lift that was used to assist with the install. Mechanic Y was in the aircraft watching the shaft to make sure that the splines were inserted into the grooves correctly. Lead mechanic X was on top of the aircraft watching the shaft from the top of the aircraft; it was at that point that I believe that the bolts were installed. These two bolts were not torqued or cotter pinned. The aircraft was then moved back into to the hangar and reassembly resumed. This was not noticed at time of reassembly of aircraft for maintenance flight following 800-hour inspections. The aircraft then flew its maintenance flight which lasted about 2-hours total flight time. The aircraft returned to ZZZ to finish up paperwork and to be placed back in service in ZZZ1. The pilot came down to swap aircraft X from aircraft Y; which they were currently in so that the pilot could take aircraft X back to ZZZ1. Aircraft X was [later] placed back into service at the ZZZ1 base. I wanted to make sure my night pilot was good with all the paper and to see if he had any questions over anything that had been completed during the maintenance evolution. He informed me that the day pilot stated that there was a 1 to 1 hop in all axis of flight; I then proceeded to ask him to let me know what he felt about the aircraft after he flew it to see if he could duplicate the 1 to 1 hop in all axis of flight. I arrived to work this morning; upon my arrival aircraft X was just starting to start engines on a patient flight. They completed patient flight without an incident. I walked out to talk to the pilot about 1 to 1 hop in all axis of flight and he said that it was there and seemed to be getting worse. I then stated to him to place aircraft X on a 30-minute maintenance delay and for us to take the aircraft for a flight to see if I could identify the 1 to 1 hop in all axis of flight. Aircraft X was then placed on a 30-minute maintenance delay. Before we got into the aircraft the pilot and I took a look at everything from the hub cap down to the mixing unit. That's when I noticed something was not correct with the hinged support attachment to the bearing block. I then pulled the co-pilot's side transmission cowling and noticed the bolts securing the hinged support to the bearing block on the co-pilot's side were not torqued nor cotter pinned. I then stopped everything took aircraft X out of service and made to notification to lead mechanic X. After speaking with lead mechanic X; I was directed to call the area maintenance manager who advised me to take the other transmission cowling off to inspect the other bolt and to take pictures and send them to him. I removed the other cowling and it was noticed the bolt was installed and the nut had worked its way off the bolt. I did a search for the nut and it was found in between the main transmission and the mixing unit. Once the nut was located I took pictures from every angle that I could see and then sent them to maintenance manager and mr. X. I informed the maintenance manager; mr. X and my lead mechanic of where the nut was located. While informing mr. X of where nut was located; he directed me to call american eurocopter technical support representative; mr. Y who was out to lunch at the time I called. Mr. Y then returned my phone call and I informed him of what was going on and he advised me to send him information stating what had happened and how it was found; along with pictures of the area. He also advised me that he would forward the pictures and statement to the design department for review and that we should have an answer back in the morning to advise us what was needed to place aircraft X back into service.I believe that there is certain action that could have been handled differently. We could have had another mechanic that was not there during the maintenance; come in and inspect everything before that aircraft was placed back into service. The extra set of eyes from someone that was not there at the time of install would have been very beneficial in the aid of identifying issues before the aircraft was placed back into a state to which it was ready to be flown for the post 800-hour flight. I also believe another mechanic could have been on hand to assist with the install of the main rotor hub shaft.

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Original NASA ASRS Text

Title: A Line Mechanic reports finding bolts that attach a hinge support to a bearing block just aft of a mixing unit; on a EC-135 Eurocopter; were not torqued or cotter pinned. Pilot had noted the EC-135 had a 1 to 1 hop in all axis of flight that had been getting worse.

Narrative: Aircraft X; a Eurocopter EC-135 was placed into Maintenance for its 800-Hour inspections. While complying with the aircraft inspections; the A-2411 Datasheet [indicated] a 1600-Hour inspection was due. The main rotor hub and the main rotor hub shaft were removed in accordance with EC-135 Maintenance Manual Chapter 62-31-00 (4-3); Removal Main Rotor Hub-Shaft; with no incident. We then carried out the inspection of the spacer tube. Upon reassembly of main rotor hub-shaft in accordance with EC-135 MM Chapter 62-31-00 (4-4); the bolts that attach the hinged support to the bearing block just aft of the mixing unit of this aircraft were installed. While installing the main rotor hub; I was on the lift that was used to assist with the install. Mechanic Y was in the aircraft watching the shaft to make sure that the splines were inserted into the grooves correctly. Lead Mechanic X was on top of the aircraft watching the shaft from the top of the aircraft; it was at that point that I believe that the bolts were installed. These two bolts were not torqued or cotter pinned. The aircraft was then moved back into to the hangar and reassembly resumed. This was not noticed at time of reassembly of aircraft for maintenance flight following 800-Hour inspections. The aircraft then flew its maintenance flight which lasted about 2-hours total flight time. The aircraft returned to ZZZ to finish up paperwork and to be placed back in service in ZZZ1. The pilot came down to swap Aircraft X from Aircraft Y; which they were currently in so that the pilot could take Aircraft X back to ZZZ1. Aircraft X was [later] placed back into service at the ZZZ1 Base. I wanted to make sure my night pilot was good with all the paper and to see if he had any questions over anything that had been completed during the maintenance evolution. He informed me that the day pilot stated that there was a 1 to 1 hop in all axis of flight; I then proceeded to ask him to let me know what he felt about the aircraft after he flew it to see if he could duplicate the 1 to 1 hop in all axis of flight. I arrived to work this morning; upon my arrival Aircraft X was just starting to start engines on a patient flight. They completed patient flight without an incident. I walked out to talk to the pilot about 1 to 1 hop in all axis of flight and he said that it was there and seemed to be getting worse. I then stated to him to place Aircraft X on a 30-minute maintenance delay and for us to take the aircraft for a flight to see if I could identify the 1 to 1 hop in all axis of flight. Aircraft X was then placed on a 30-minute maintenance delay. Before we got into the aircraft the pilot and I took a look at everything from the hub cap down to the mixing unit. That's when I noticed something was not correct with the hinged support attachment to the bearing block. I then pulled the Co-Pilot's side transmission cowling and noticed the bolts securing the hinged support to the bearing block on the Co-Pilot's side were not torqued nor cotter pinned. I then stopped everything took Aircraft X out of service and made to notification to Lead Mechanic X. After speaking with Lead Mechanic X; I was directed to call the Area Maintenance Manager who advised me to take the other transmission cowling off to inspect the other bolt and to take pictures and send them to him. I removed the other cowling and it was noticed the bolt was installed and the nut had worked its way off the bolt. I did a search for the nut and it was found in between the main transmission and the mixing unit. Once the nut was located I took pictures from every angle that I could see and then sent them to Maintenance Manager and Mr. X. I informed the Maintenance Manager; Mr. X and my Lead Mechanic of where the nut was located. While informing Mr. X of where nut was located; he directed me to call American Eurocopter Technical Support Representative; Mr. Y who was out to lunch at the time I called. Mr. Y then returned my phone call and I informed him of what was going on and he advised me to send him information stating what had happened and how it was found; along with pictures of the area. He also advised me that he would forward the pictures and statement to the design department for review and that we should have an answer back in the morning to advise us what was needed to place Aircraft X back into service.I believe that there is certain action that could have been handled differently. We could have had another Mechanic that was not there during the maintenance; come in and inspect everything before that aircraft was placed back into service. The extra set of eyes from someone that was not there at the time of install would have been very beneficial in the aid of identifying issues before the aircraft was placed back into a state to which it was ready to be flown for the post 800-Hour flight. I also believe another Mechanic could have been on hand to assist with the install of the main rotor hub shaft.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.