Narrative:

Three mechanics; one bell-407 trained; were installing the main rotor head for scheduled FAA approved aircraft inspection program (aaip) inspections. During lowering the rotor head onto the mast; binding occurred once it was about halfway engaged. The rotor head was raised; checked for master-spline alignment and verified by all of us. We lowered the rotor head again and had the same result. We raised the head again and inspected the splines on the mast and rotor. We repositioned the hoist to ensure proper alignment and reviewed the maintenance manual (M/M) to ensure we hadn't missed any steps. I noted that last year; during the same inspection; the rotor was very difficult to remove and reinstall. It was also noted to me by the previous mechanic that maintained this aircraft; that the rotor head was very hard to remove and reinstall. We then consulted another experienced bell-407 mechanic and were told that these [rotor] heads can be very hard to go on. I then noted that last year; there were four mechanics; two of which weighed considerably more than any of us; were applying all their weight to the rotor head while shaking and got it to move into position. We then lowered the rotor onto the mast again and insured proper master-spline engagement. We shook the head and applied our weight in an attempt to get it to go on. We then used ratchet straps; around the transmission legs and rotor top-plate; careful to avoid any other parts; to apply firm; even pressure on the rotor head. With the pressure applied; we then used 2-lb (pound) rubber mallets to hit the top of the head. Movement of the rotor going on was observed; so we continued and the head went on very quickly. Tooling damage from one of the rubber mallets was observed on the rotor head top plate. We consulted the maintenance manual (M/M) and found to be within limits. We then continued the installation in accordance with the bell 407 M/M and no other issues were encountered. The next day; after a call of concern from a maintenance manager; the installation procedure was reviewed again. It was found in a note; that if restriction is encountered while lowering the main rotor hub assembly on the mast; the rotor through bolts may be loosened and re-torqued once the rotor is in position. This particular aircraft is the only one I have had the experience of removing; or installing; a main rotor; in which case the use of 'force' seemed normal. I am mechanic at a one-man base and was new to the bell-407 when placed there. I never had the privilege of working under other skilled bell-407 mechanics. My bell-407 school was a one week course; at another helicopter base; with all classroom training and no practical hands-on. A mechanic has the ability to read the maintenance manual (M/M) and follow procedures; but in a case like the above; you don't really know what is 'normal versus excessive.' this work was also being performed away from the aircraft base and my home; so there was pressure to get the job done so that I could get back home to my family. I feel that my experience was limited; to be performing this heavy maintenance without the presence of a more experienced bell-407 mechanic.

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Original NASA ASRS Text

Title: An Aircraft Maintenance Technician (AMT) with limited experience on Bell helicopters describes his efforts to re-install a Main Rotor Hub Assembly onto the mast of a BHT-407 rotorcraft.

Narrative: Three mechanics; one Bell-407 trained; were installing the Main Rotor Head for scheduled FAA Approved Aircraft Inspection Program (AAIP) inspections. During lowering the rotor head onto the mast; binding occurred once it was about halfway engaged. The Rotor Head was raised; checked for master-spline alignment and verified by all of us. We lowered the rotor head again and had the same result. We raised the head again and inspected the splines on the mast and rotor. We repositioned the hoist to ensure proper alignment and reviewed the Maintenance Manual (M/M) to ensure we hadn't missed any steps. I noted that last year; during the same inspection; the rotor was very difficult to remove and reinstall. It was also noted to me by the previous Mechanic that maintained this aircraft; that the rotor head was very hard to remove and reinstall. We then consulted another experienced Bell-407 Mechanic and were told that these [rotor] heads can be very hard to go on. I then noted that last year; there were four mechanics; two of which weighed considerably more than any of us; were applying all their weight to the rotor head while shaking and got it to move into position. We then lowered the rotor onto the mast again and insured proper master-spline engagement. We shook the head and applied our weight in an attempt to get it to go on. We then used ratchet straps; around the transmission legs and rotor top-plate; careful to avoid any other parts; to apply firm; even pressure on the rotor head. With the pressure applied; we then used 2-lb (pound) rubber mallets to hit the top of the head. Movement of the rotor going on was observed; so we continued and the head went on very quickly. Tooling damage from one of the rubber mallets was observed on the rotor head top plate. We consulted the Maintenance Manual (M/M) and found to be within limits. We then continued the installation IAW the Bell 407 M/M and no other issues were encountered. The next day; after a call of concern from a Maintenance Manager; the installation procedure was reviewed again. It was found in a note; that if restriction is encountered while lowering the Main Rotor Hub Assembly on the mast; the rotor through bolts may be loosened and re-torqued once the rotor is in position. This particular aircraft is the only one I have had the experience of removing; or installing; a Main Rotor; in which case the use of 'force' seemed normal. I am Mechanic at a one-man Base and was new to the Bell-407 when placed there. I never had the privilege of working under other skilled Bell-407 mechanics. My Bell-407 school was a one week course; at another helicopter base; with all classroom training and no practical hands-on. A Mechanic has the ability to read the Maintenance Manual (M/M) and follow procedures; but in a case like the above; you don't really know what is 'normal versus excessive.' This work was also being performed away from the aircraft base and my home; so there was pressure to get the job done so that I could get back home to my family. I feel that my experience was limited; to be performing this heavy maintenance without the presence of a more experienced Bell-407 Mechanic.

Data retrieved from NASA's ASRS site 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.