Narrative:

This plane is owned by ten people in a partnership/club. The annual inspection was completed approximately six weeks ago and I had not flown this plane since then (having access to another aircraft as well). During the preflight inspection today; I found that the three inspection plates - two on the bottom of the cabin; one on the bottom of the engine compartment; at the front of the fuselage; were missing. Each plate is round; approximately six inches in diameter and secured by three screws. Two of the open inspection holes had one screw in place; and the third had no screws present. The typical procedure when performing an inspection is to remove two screws; loosen the third; swing the plate out of the way and secure the two remaining screws in their holes until the panel is secured. The annual inspection was owner-assisted. Several of the aircraft's owners removed the inspection panels; seats and cowling. An a&P/ia performed the inspection; necessary repairs and signed the aircraft and engine logs after the inspection having found the aircraft to be in an airworthy condition.the inspection plates; seats; and cowling were reinstalled by one of the owners who had removed them. The missing panels and screws were not located. Between the annual inspection and today; the plane had been flown three times and taxied twice; for a total of approximately three hours of operation. It appears that what most likely happened was that the inspection panels were not properly reinstalled upon completion of the annual inspection; and the screws vibrated loose during aircraft operation; causing the panels to fall from the aircraft. It is not known when; where or during what phase of flight that event occurred. To the best of my knowledge; there were no incidents of damage or injuries caused by the panels departing the aircraft; so it is not likely that the exact time; phase of flight; and pilot involved can be identified. No other anomalies were found.the problem was corrected by installation of the proper inspection panels and screws. The most probable cause for this was due to inadequate maintenance procedures and by inadequate preflight inspections. When reinstalling inspection panels; seats; and cowlings following maintenance; the work should be inspected and verified as secure by someone other than the person doing the work. That will allow a fresh set of eyes to locate any improperly done work or other improper condition. In this case; it is obvious that the person doing the work was either careless or distracted; an independent inspector could have caught this. (I have not been able to determine which one of my partners is responsible. I was not present when the annual was completed.) a thorough preflight inspection should include inspection of the aircraft's belly. In addition to missing or loose inspection plates; other problems such as leaks; loose antennas; or foreign object damage can be detected. The pilots who flew the aircraft with the inspection plates loose or missing could not have performed adequate preflight inspections and not found three open holes in the belly.it is especially necessary to conduct a much more detailed preflight after any maintenance is performed. In summary; people performing maintenance should:-take steps to minimize or remove distractions when performing pre/during/post maintenance actions.-have someone else do a quality assurance check.-always perform a thorough preflight inspection before the first flight of the day; for each new pilot/aircrew and after any maintenance.-be a nitpicky perfectionist.

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Original NASA ASRS Text

Title: A C172 pilot reported finding three inspection plates missing from the bottom of the aircraft six weeks after an annual inspection.

Narrative: This plane is owned by ten people in a partnership/club. The annual inspection was completed approximately six weeks ago and I had not flown this plane since then (having access to another aircraft as well). During the preflight inspection today; I found that the three inspection plates - two on the bottom of the cabin; one on the bottom of the engine compartment; at the front of the fuselage; were missing. Each plate is round; approximately six inches in diameter and secured by three screws. Two of the open inspection holes had one screw in place; and the third had no screws present. The typical procedure when performing an inspection is to remove two screws; loosen the third; swing the plate out of the way and secure the two remaining screws in their holes until the panel is secured. The annual inspection was owner-assisted. Several of the aircraft's owners removed the inspection panels; seats and cowling. An A&P/IA performed the inspection; necessary repairs and signed the aircraft and engine logs after the inspection having found the aircraft to be in an airworthy condition.The inspection plates; seats; and cowling were reinstalled by one of the owners who had removed them. The missing panels and screws were not located. Between the annual inspection and today; the plane had been flown three times and taxied twice; for a total of approximately three hours of operation. It appears that what most likely happened was that the inspection panels were not properly reinstalled upon completion of the annual inspection; and the screws vibrated loose during aircraft operation; causing the panels to fall from the aircraft. It is not known when; where or during what phase of flight that event occurred. To the best of my knowledge; there were no incidents of damage or injuries caused by the panels departing the aircraft; so it is not likely that the exact time; phase of flight; and pilot involved can be identified. No other anomalies were found.The problem was corrected by installation of the proper inspection panels and screws. The most probable cause for this was due to inadequate maintenance procedures and by inadequate preflight inspections. When reinstalling inspection panels; seats; and cowlings following maintenance; the work should be inspected and verified as secure by someone other than the person doing the work. That will allow a fresh set of eyes to locate any improperly done work or other improper condition. In this case; it is obvious that the person doing the work was either careless or distracted; an independent Inspector could have caught this. (I have not been able to determine which one of my partners is responsible. I was not present when the annual was completed.) A thorough preflight inspection should include inspection of the aircraft's belly. In addition to missing or loose inspection plates; other problems such as leaks; loose antennas; or foreign object damage can be detected. The pilots who flew the aircraft with the inspection plates loose or missing could not have performed adequate preflight inspections and not found three open holes in the belly.It is especially necessary to conduct a much more detailed preflight after any maintenance is performed. In summary; people performing maintenance should:-Take steps to minimize or remove distractions when performing pre/during/post maintenance actions.-Have someone else do a quality assurance check.-Always perform a thorough preflight inspection before the first flight of the day; for each new pilot/aircrew and after any maintenance.-Be a nitpicky perfectionist.

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.