While performing an engine overhaul on a customer's single-engine aircraft, an A&P mechanic employed by an FAA-certified aircraft repair station is distracted by a telephone call. Returning to the nearly-completed task, the mechanic replaces the engine cowling without first securing the oil sump drain plug with safety wire as required by the maintenance manual. The shop foreman, who holds FAA Inspection Authorization, signs off the overhaul and approves the aircraft for return to service without noticing the oversight. The owner-pilot picks up the aircraft and conducts a preflight inspection meticulously following the instructions in the aircraft operator's manual. The manual does not mention the oil sump drain plug, which is not easily visible. The owner-pilot takes off for an engine break-in flight. While in flight, the drain plug vibrates loose, the engine oil is lost overboard, and the engine seizes. The pilot makes an emergency landing in what looks like the most suitable spot within gliding range, a plowed field, where the aircraft overturns. The aircraft is substantially damaged, and the pilot is seriously injured.

Who is potentially legally liable for these damages and personal injuries, and why?