What happened
On May 7, 2017, an Airbus A321-211 operated by Small Planet Airlines was performing a departure from Heraklion Airport (LGIR) in Greece. During the climb phase, the flight crew identified low oil pressure in engine number one, although all other engine parameters remained within normal operating ranges.
In response to the pressure drop, the crew leveled off the aircraft at 6,000 ft and notified Air Traffic Control of their intention to return to the departure airport. After verifying the landing weight, the crew executed a standard approach and landed safely at Heraklion.
The investigation
Following the landing, ground maintenance personnel at Heraklion (MRO Aerocandia) inspected the aircraft and identified an oil leak. The investigation established that the leak originated from a loosened drain plug located on the oil filter housing of engine number one.
The investigation further traced the maintenance history of the aircraft, finding that the most recent oil filter service for both engines had been performed by a maintenance organization on March 22, 2017. This organization was notified of the incident and conducted its own internal inquiry, which confirmed the findings regarding the faulty plug security.