Narrative:

Mechanic 'a' and I volunteered to help with an engine change on a crj-900 aircraft. When we arrived; we were tasked with getting the bad engine ready for removal from the crj-900; while local maintenance removed the cannibalized (robbed) engine off of another -900. We worked by ourselves most of the time; and I prepped the forward engine mount for removal by cutting the safety wire and loosening the retainer bolts from the pylon side of the engine mount/yoke. While in the hanger; I took several pictures of the hanger and the crj-900 engine change process for my own use.after reviewing the pictures [two days later]; I noticed that the engine mount yoke was still installed on the pylon with the engine removed. I loosened up the hardware of the yoke to remove it from the pylon; not the engine. This is the exact opposite procedure that I am familiar with while changing a crj-200 engine. After figuring out I loosened the hardware from the wrong side of the yoke; we contacted the local maintenance to determine if the hardware was retorqued and safetied. We could not get in touch with anyone that I knew. So we called maintenance control to ground the aircraft until it could be determined if the hardware was torqued and safetied. It was later determined that the hardware was indeed torqued and safetied.I figured out the yoke was loosened at the wrong point myself while reviewing pictures of the road trip once I was back at home. I noticed the yoke still installed on the pylon instead of the engine as I am accustomed to on a crj-200 engine change.we had access to the crj-900 engine change task card which clearly showed where to disconnect the engine mount yoke. We had fallen behind schedule while removing the pylon panels due to many screws that needed to be drilled out. We worked as fast as possible to remove the lines and plugs from the engine/pylon area. When it came time to remove the hardware from the engine mounts in preparation for the removal; I simply assumed that the sequence and location of the components was the same as that of a -200 removal due to the familiarity of the components. When we finally did remove the engine I was not in a position to see what hardware was actually removed. At that point in the shift; I had been up for 20 hours and we were getting ready to head to our hotel. I made no notice of what had actually been disconnected from the engine and pylon. This event occurred simply because I assumed the engine removal procedure was the same as a crj-200 due to the similarity of the hardware.once the problem was noted; we asked maintenance control to ground the aircraft until the yoke to pylon attach point could be verified torqued and safetied; which it was found to be. Simply reviewing the task card would have avoided this situation.

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Original NASA ASRS Text

Title: Three Mechanics reported a left engine change on a CRJ-900 aircraft. One of the Mechanic's assumed the disconnect procedures for the CRJ-900's were the same as those on the CRJ-200; but they were not. Incorrect procedures were used.

Narrative: Mechanic 'A' and I volunteered to help with an engine change on a CRJ-900 aircraft. When we arrived; we were tasked with getting the bad engine ready for removal from the CRJ-900; while Local Maintenance removed the cannibalized (robbed) engine off of another -900. We worked by ourselves most of the time; and I prepped the forward engine mount for removal by cutting the safety wire and loosening the retainer bolts from the pylon side of the engine mount/yoke. While in the hanger; I took several pictures of the hanger and the CRJ-900 engine change process for my own use.After reviewing the pictures [two days later]; I noticed that the engine mount yoke was still installed on the pylon with the engine removed. I loosened up the hardware of the yoke to remove it from the pylon; not the engine. This is the exact opposite procedure that I am familiar with while changing a CRJ-200 engine. After figuring out I loosened the hardware from the wrong side of the yoke; we contacted the Local Maintenance to determine if the hardware was retorqued and safetied. We could not get in touch with anyone that I knew. So we called Maintenance Control to ground the aircraft until it could be determined if the hardware was torqued and safetied. It was later determined that the hardware was indeed torqued and safetied.I figured out the yoke was loosened at the wrong point myself while reviewing pictures of the road trip once I was back at home. I noticed the yoke still installed on the pylon instead of the engine as I am accustomed to on a CRJ-200 engine change.We had access to the CRJ-900 Engine Change Task Card which clearly showed where to disconnect the engine mount yoke. We had fallen behind schedule while removing the pylon panels due to many screws that needed to be drilled out. We worked as fast as possible to remove the lines and plugs from the engine/pylon area. When it came time to remove the hardware from the engine mounts in preparation for the removal; I simply assumed that the sequence and location of the components was the same as that of a -200 removal due to the familiarity of the components. When we finally did remove the engine I was not in a position to see what hardware was actually removed. At that point in the shift; I had been up for 20 hours and we were getting ready to head to our hotel. I made no notice of what had actually been disconnected from the engine and pylon. This event occurred simply because I assumed the engine removal procedure was the same as a CRJ-200 due to the similarity of the hardware.Once the problem was noted; we asked Maintenance Control to ground the aircraft until the yoke to pylon attach point could be verified torqued and safetied; which it was found to be. Simply reviewing the Task Card would have avoided this situation.

Data retrieved from NASA's ASRS site as of April 2012 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.