Date: 201206
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Light: Night
Aircraft: B717 (Formerly MD-95)
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Air Conditioning Compressor
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Confusion; Communication Breakdown; Distraction; Fatigue; Situational Awareness; Time Pressure; Workload
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
Result: General None Reported / Taken
Contributing factors: Human Factors; Weather
Primary problem: Human Factors

Narrative: I; Mechanic X; was assigned to Aircraft X; a B717; on the Routine Overnight (RON) Line with Mechanic Y (performing Water Purification) and Mechanic Z (performing Service Check). Aircraft X was set to arrive in the morning with a departure time eight and a half hours later. I was assigned to perform a non-regular task of an Air Cycle Machine (ACM) Change and expected to finish within set time limitations. Upon receiving my assignment from the Lead Mechanic; I began to read through the Task Card and obtain all my necessary documentation; tooling and other items I would need to accomplish the ACM change. As soon as Aircraft X arrived to the gate; we all jumped on to perform our Scheduled Maintenance Tasks as quickly as possible; given that we only had a very limited window to accomplish all of our tasks.I pulled all my necessary Circuit Breakers; per the Task Card; and began to remove the right-hand ACM. Once removed; I replaced the ACM with the Serviceable ACM provided. Upon completion of the installation of the ACM; it now being 90-minutes before departure; I noticed that there was a damaged clamp on the Coalescer housing. By this time I was forced to turn the remainder of the task over to the next shift because I needed to return to the hangar in order clean-up and punch out within thirty minutes; which I did not make and ended up punching out forty-five minutes later. I returned to work again the following night to find that the mechanics I turned to the task over to realized that the wrong ACM was replaced. I inadvertently replaced the right side ACM when the left side ACM was scheduled to be replaced. I believe that this error occurred for multiple reasons. When we were assigned our aircraft by our Lead Mechanic; we were not assigned to specific tasks. I offered to take the heavier work load of the ACM replacement. Once I; and Mechanic Y and Z decided how to split the workload amongst ourselves; I immediately looked on the front page of the Task Card to determine which ACM I needed to replace. This is not a normal task that is performed on a regular basis; so the Task Card read a little different than others. The first item I noticed was the very left corner of the Task Card; where I now see it states 'R/R'. When first seeing this area of the Task Card; I mistakenly identified it as the location of which ACM to change and being that it had an 'R'; I concluded that the right ACM needed replaced; so I never re-read that portion of the card because I'd determined that I got all the information I needed from that area.Another big reason I believe this mistake occurred was because the lack of communication between the Lead Mechanic and myself. An ACM change is a fairly heavy workload and special consideration should be taken on heavier work assignments. There was no special consideration or instruction provided by my Lead nor my Manager outside of the regular; 'how much longer' or 'are you almost done'. Those were the extent of the communications between us throughout the night. If more attention and consideration is given to heavier assignments; i.e. verifying that the mechanic understands the job and has the proper tooling and equipment to perform the job; then perhaps mistakes like this may not occur. Lastly; I believe that environmental situations and fatigue was another big factor in this mistake. I was coming on the job on 'my' Monday and little rest throughout the day before due to my home and family obligations. I was awake very early the morning of the event and by the time I was performing the ACM change; I had been actively awake for 15 hours. Then; once performing the Task; the lack of ventilation made it excessively hot in the location where the ACM is located; especially since the compartment where the ACM is located is the same compartment as the APU; which was running just prior to the aircraft's arrival and [continues to] dissipates heat in excess of 600-degrees for a good period even after shutdown.But I did not have time to wait for the compartment to cool down because the flight was due out in the morning and; again; the aircraft did not arrive until late at night; so I had approximately seven hours to complete a very time consuming task. I believe better planning and communication with heavier work loads should take a bit more priority and more assertiveness from the high Management and Leads. Better planning; so to allow more ground time for the aircraft for time consuming tasks; allows for a not only more time and less stress of time constraints; but it also would allow more time for cooling off the work area and allow more time to setup a better ventilated area. Also; the Task Card is generic to the task to be performed. It provides instruction for both Left and Right ACM replacements and never instructs you on where to look to find and verify that you are performing the replacement on the correct ACM. It does; however; have a Location section on the Task Card so you can know which one to replace; but it never instructs you to look there and verify Part Number's (P/N's); Serial Number's (S/N's) or locations; it simply begins removal [instructions] of the ACM for either side; excessive heat.




Synopsis: A Line Mechanic inadvertently replaced the right side Air Cycle Machine (ACM) when the left side ACM was scheduled to be replaced on a B717 aircraft while trying to meet a morning departure schedule.