Narrative:

The bell 206L aircraft had been in an far 135-heavy maintenance facility where it had the transmission replaced. It was released as airworthy and after approximately 50-hours flight time; the flight crew heard an unusual noise and the pilot made a precautionary landing.the base mechanic was dispatched to the aircraft where he performed a visual inspection and couldn't find any obvious source of the noise. The pilot and mechanic flew the aircraft back to base; the noise was not present for the flight back. While the mechanic was investigating a transmission oil leak back at the [maintenance] base; he discovered the bolts attaching the main drive shaft to the transmission were loose.I believe a contributing factor was failure by the installing mechanic to complete the installation of the fasteners [bolts] before moving to a different step of the job. I believe human factors involved in this incident are fatigue; complacency; and the pressure by management to maintain a high tempo of production at their heavy maintenance facilities.the company's 135-heavy maintenance was restructured just over a year ago. The 135-heavy maintenance of approximately 118 aircraft had been divided between X number of heavy maintenance bases; but now down to four. The scope of work now is more what you would expect at a 145-repair facility; which the company has; but the [remaining] 145-repair facilities can't keep up with company needs. Work at this facility is being performed 14-hours a day using split shifts; and 365 days a year using two crews of four mechanics; each crew working seven days 'on'; seven days 'off' hitches. At this facility; there are only seven mechanics instead of the full crew of eight. Out of the seven mechanics; four are housed in living quarters in the hangar during their hitch. This facility is also used for 'after' hours parts support for 25 of the company's field bases. This facility is located on a regional airport approximately 100 yards from the runway and with a four lane highway approximately 30 yards on the other side and directly on a tarmac for a flight school and business jets. So it is difficult to get proper rest. This along with the increased work load and high production tempo leads to a chronic; low to mid level of constant fatigue.I think a corrective action might be to put in place a quality assurance (Q/a) department whose sole job is to 'buy off' on flight safety critical maintenance procedures before the maintenance can even proceed. And also move the living quarters offsite. The current procedure in place is the mechanic performing an install; prints out the install procedures from the maintenance manual (M/M) and initials each step. If he has to stop the job for any reason he puts a red mark after the last step he completes. The mechanic that resumes the job whether it is another mechanic or himself has to go back and verify [that] the three steps before the red line have been completed; before he can proceed. The maintenance records do not require the initials or signature of another mechanic on a flight safety critical step of a job before proceeding. The suggested practice is to get someone else to look the job over; but is not required to be documented in any way.I was not the installing mechanic; but I initialed one block of an approved aircraft inspection program (aaip) checklist for the main drive shaft area. Since the inspection form block doesn't require a date; I cannot prove I performed a visual inspection of the drive shaft before it was known the aircraft needed the transmission replaced; so I am self disclosing.

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Original NASA ASRS Text

Title: Four Aircraft Maintenance Technician (AMT) reports about working conditions at an FAR 135 repair facility that included fatigue; complacency; the lack of an Inspection Department and the lack of adequate maintenance procedures that eventually led to one of their pilot's performing a precautionary landing of a Bell 206L helicopter.

Narrative: The Bell 206L aircraft had been in an FAR 135-Heavy Maintenance facility where it had the transmission replaced. It was released as airworthy and after approximately 50-hours flight time; the flight crew heard an unusual noise and the pilot made a precautionary landing.The Base Mechanic was dispatched to the aircraft where he performed a visual inspection and couldn't find any obvious source of the noise. The pilot and Mechanic flew the aircraft back to base; the noise was not present for the flight back. While the Mechanic was investigating a transmission oil leak back at the [Maintenance] Base; he discovered the bolts attaching the Main Drive Shaft to the transmission were loose.I believe a contributing factor was failure by the installing Mechanic to complete the installation of the fasteners [bolts] before moving to a different step of the job. I believe human factors involved in this incident are fatigue; complacency; and the pressure by Management to maintain a high tempo of production at their Heavy Maintenance facilities.The company's 135-Heavy Maintenance was restructured just over a year ago. The 135-Heavy Maintenance of approximately 118 aircraft had been divided between X number of Heavy Maintenance bases; but now down to four. The scope of work now is more what you would expect at a 145-repair facility; which the company has; but the [remaining] 145-repair facilities can't keep up with company needs. Work at this facility is being performed 14-hours a day using split shifts; and 365 days a year using two crews of four mechanics; each crew working seven days 'on'; seven days 'off' hitches. At this facility; there are only seven mechanics instead of the full crew of eight. Out of the seven mechanics; four are housed in living quarters in the hangar during their hitch. This facility is also used for 'after' hours parts support for 25 of the company's field bases. This facility is located on a regional airport approximately 100 yards from the runway and with a four lane highway approximately 30 yards on the other side and directly on a tarmac for a flight school and business jets. So it is difficult to get proper rest. This along with the increased work load and high production tempo leads to a chronic; low to mid level of constant fatigue.I think a corrective action might be to put in place a Quality Assurance (Q/A) Department whose sole job is to 'Buy Off' on Flight Safety Critical maintenance procedures before the maintenance can even proceed. And also move the living quarters offsite. The current procedure in place is the mechanic performing an install; prints out the install procedures from the Maintenance Manual (M/M) and initials each step. If he has to stop the job for any reason he puts a red mark after the last step he completes. The mechanic that resumes the job whether it is another mechanic or himself has to go back and verify [that] the three steps before the red line have been completed; before he can proceed. The Maintenance Records do not require the initials or signature of another mechanic on a Flight Safety Critical step of a job before proceeding. The suggested practice is to get someone else to look the job over; but is not required to be documented in any way.I was not the installing mechanic; but I initialed one block of an Approved Aircraft Inspection Program (AAIP) Checklist for the Main Drive Shaft area. Since the inspection form block doesn't require a date; I cannot prove I performed a visual inspection of the drive shaft before it was known the aircraft needed the transmission replaced; so I am self disclosing.

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.