Narrative:

[As the] maintenance manager; I was troubleshooting a smoke in the cabin issue after the hawker-800 plane got back from a trip. The smoke was reported at the beginning of the trip so the APU was MEL'd. It came back and I found that the APU would not rotate when starter was engaged. Removed APU starter/generator and found that it rotated; so I determined the APU was seized. I went and worked on another airplane to give myself a rest from the [physical] positions you are in; doing this job. I left the generator on my tool box. I came back later and found my box and the generator gone so I assumed that it got installed by another mechanic. I did not verify that it was installed; I just assumed. I went in and signed-off the paper and the aircraft was released.we sent the aircraft to a third party maintenance vendor in ZZZ1 to have the APU removed and the seized turbine repaired. They repaired the APU and reinstalled it into airplane. The APU generator was found to be uninstalled during the logbook paperwork release. The far part 135 maintenance guy found on the work card that there was no 'off' serial number (south/north) [for the starter generator and called the maintenance vendor. Maintenance called me and told me the generator was not installed when it arrived at the vendor. I told maintenance that it was and it is a mistake by them. I was then out in my workshop getting items ready for calibration and spotted a generator on a work shelf. Wrote down serial number (south/north) and consulted the continuous airworthiness maintenance program (camp). It was the serial number that should have been on the APU when it got to the third party vendor. I called quality control (qc) and told them that they were correct and I had the generator that was not reinstalled as I had stated in the log entry/corrective action on the work order. As far as me being a mechanic; I need to remember to never assume that something was completed. I need to always verify the condition of the planes I work on; to ensure they are safe and in the condition they are reported to be in. I need to document tasks better and I will from now on hang a streamer and a red tag stating; 'do not remove until maintenance is complete' on the side of the aircraft. This tag will be close to the area worked; if it is a single job; and it will list that task. I need to finish the task at hand before I go to another task.

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Original NASA ASRS Text

Title: A Maintenance Manager reports he signed off the Maintenance Release for a Hawker-800 aircraft after assuming; and without verifying; that a Starter/Generator unit he had previously removed had been reinstalled on the aircraft's APU.

Narrative: [As the] Maintenance Manager; I was troubleshooting a smoke in the cabin issue after the Hawker-800 plane got back from a trip. The smoke was reported at the beginning of the trip so the APU was MEL'd. It came back and I found that the APU would not rotate when starter was engaged. Removed APU Starter/Generator and found that it rotated; so I determined the APU was seized. I went and worked on another airplane to give myself a rest from the [physical] positions you are in; doing this job. I left the generator on my tool box. I came back later and found my box and the generator gone so I assumed that it got installed by another Mechanic. I did not verify that it was installed; I just assumed. I went in and signed-off the paper and the aircraft was released.We sent the aircraft to a third party Maintenance Vendor in ZZZ1 to have the APU removed and the seized turbine repaired. They repaired the APU and reinstalled it into airplane. The APU generator was found to be uninstalled during the Logbook paperwork release. The FAR Part 135 Maintenance guy found on the Work Card that there was no 'Off' Serial Number (S/N) [for the Starter Generator and called the Maintenance Vendor. Maintenance called me and told me the generator was not installed when it arrived at the Vendor. I told Maintenance that it was and it is a mistake by them. I was then out in my workshop getting items ready for calibration and spotted a generator on a work shelf. Wrote down Serial Number (S/N) and consulted the Continuous Airworthiness Maintenance Program (CAMP). It was the Serial Number that should have been on the APU when it got to the third party Vendor. I called Quality Control (QC) and told them that they were correct and I had the generator that was not reinstalled as I had stated in the Log Entry/Corrective Action on the Work Order. As far as me being a Mechanic; I need to remember to never assume that something was completed. I need to always verify the condition of the planes I work on; to ensure they are safe and in the condition they are reported to be in. I need to document tasks better and I will from now on hang a streamer and a red tag stating; 'Do Not Remove Until Maintenance Is Complete' on the side of the aircraft. This tag will be close to the area worked; if it is a single job; and it will list that task. I need to finish the task at hand before I go to another task.

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.