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 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 injuries, and why?