Narrative:

During routine oil change; I allowed an assistant to remove the engine cowling and drain the engine oil while I performed other maintenance functions. The assistant also removed the safety wire and loosened both the oil sump screen cover and oil filter. At this point I took over the oil change; changing the filter and replenishing the engine oil. The owner of the aircraft informed me at this point that he would likely need the aircraft as soon as possible to fly to a business meeting. At this point; I pulled out the aircraft and performed a run-up and leak check which was good. I did not notice the oil sump drain cover safety wire was removed and made the assumption the screen was checked; reinstalled and secured by my assistant. I then installed the cowling and returned the aircraft to service. The owner decided to not use the aircraft and it was used later in the day for flight training. During this training flight; a loss of oil pressure was noted by the instructor at which time a precautionary landing was made in ZZZ1. Upon landing; a massive oil leak was noted. Local mechanics removed the cowling and found the sump drain cover missing. Lack of communication between myself and my assistant plus the time pressure to get the aircraft returned to service for the owner were contributing factors in this event. I have discussed this matter at length with the assistant and we have agreed to improve our communication and discussed the importance of passing along a complete job status update when turning work over and the dangers of disassembling aircraft components without reassembly or some type of documentation of partial work accomplished. Valuable lessons were learned from this event by both my assistant and myself that we will cary with us in the future. Callback conversation with reporter revealed the following information: reporter stated the cessna-172 lycoming engine oil sump drain cover has a 1 inch nut that secures the cover; which he failed to safety wire. Because of the loss of oil pressure; he recommended the engine be disassembled before further flight. The engine crank journal was found scored; so a complete engine overhaul was initiated.

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Original NASA ASRS Text

Title: AFTER PERFORMING ROUTINE ENGINE OIL AND FILTER CHANGE ON A CESSNA-172; MECHANIC IS INFORMED THE ENG SUMP SCREEN COVER HAD SEPARATED DURING FLT TRAINING; CAUSING OIL PRESSURE LOSS AND PRECAUTIONARY LANDING.

Narrative: DURING ROUTINE OIL CHANGE; I ALLOWED AN ASSISTANT TO REMOVE THE ENG COWLING AND DRAIN THE ENG OIL WHILE I PERFORMED OTHER MAINT FUNCTIONS. THE ASSISTANT ALSO REMOVED THE SAFETY WIRE AND LOOSENED BOTH THE OIL SUMP SCREEN COVER AND OIL FILTER. AT THIS POINT I TOOK OVER THE OIL CHANGE; CHANGING THE FILTER AND REPLENISHING THE ENG OIL. THE OWNER OF THE ACFT INFORMED ME AT THIS POINT THAT HE WOULD LIKELY NEED THE ACFT ASAP TO FLY TO A BUSINESS MEETING. AT THIS POINT; I PULLED OUT THE ACFT AND PERFORMED A RUN-UP AND LEAK CHK WHICH WAS GOOD. I DID NOT NOTICE THE OIL SUMP DRAIN COVER SAFETY WIRE WAS REMOVED AND MADE THE ASSUMPTION THE SCREEN WAS CHKED; REINSTALLED AND SECURED BY MY ASSISTANT. I THEN INSTALLED THE COWLING AND RETURNED THE ACFT TO SVC. THE OWNER DECIDED TO NOT USE THE ACFT AND IT WAS USED LATER IN THE DAY FOR FLT TRAINING. DURING THIS TRAINING FLT; A LOSS OF OIL PRESSURE WAS NOTED BY THE INSTRUCTOR AT WHICH TIME A PRECAUTIONARY LNDG WAS MADE IN ZZZ1. UPON LNDG; A MASSIVE OIL LEAK WAS NOTED. LCL MECHS REMOVED THE COWLING AND FOUND THE SUMP DRAIN COVER MISSING. LACK OF COM BTWN MYSELF AND MY ASSISTANT PLUS THE TIME PRESSURE TO GET THE ACFT RETURNED TO SVC FOR THE OWNER WERE CONTRIBUTING FACTORS IN THIS EVENT. I HAVE DISCUSSED THIS MATTER AT LENGTH WITH THE ASSISTANT AND WE HAVE AGREED TO IMPROVE OUR COM AND DISCUSSED THE IMPORTANCE OF PASSING ALONG A COMPLETE JOB STATUS UPDATE WHEN TURNING WORK OVER AND THE DANGERS OF DISASSEMBLING ACFT COMPONENTS WITHOUT REASSEMBLY OR SOME TYPE OF DOCUMENTATION OF PARTIAL WORK ACCOMPLISHED. VALUABLE LESSONS WERE LEARNED FROM THIS EVENT BY BOTH MY ASSISTANT AND MYSELF THAT WE WILL CARY WITH US IN THE FUTURE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE CESSNA-172 LYCOMING ENGINE OIL SUMP DRAIN COVER HAS A 1 INCH NUT THAT SECURES THE COVER; WHICH HE FAILED TO SAFETY WIRE. BECAUSE OF THE LOSS OF OIL PRESSURE; HE RECOMMENDED THE ENGINE BE DISASSEMBLED BEFORE FURTHER FLIGHT. THE ENGINE CRANK JOURNAL WAS FOUND SCORED; SO A COMPLETE ENGINE OVERHAUL WAS INITIATED.

Data retrieved from NASA's ASRS site as of May 2009 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.