Overview
On 28 February 2018 at 15:04 UTC, a Smartlynx Airlines Estonia Airbus A320-214, registered ES-SAN, was conducting training flights near Tallinn Airport. The aircraft had taken off at 10:02 UTC with a crew of two (captain and safety pilot), four students, and one ECAA inspector. After several successful ILS approaches and touch-and-go cycles, the aircraft experienced an abnormal event following a successful touchdown.
Sequence of Events
After touchdown, the aircraft did not respond as expected to sidestick inputs when reaching rotation speed. It briefly lifted off, then lost altitude and struck the ground near the end of the runway. The engines impacted the runway, and the landing gear doors were damaged. The aircraft then climbed to 1590 feet above ground level and pitched down again. The pilots stabilized the flight path using manual pitch trim and engine thrust, performed a U-turn back toward the runway, and declared an emergency. The aircraft was cleared for an emergency landing. During the approach, both engines lost power. The aircraft landed 150 meters before the runway threshold, causing tire bursts and a veer off the runway, finally stopping 15 meters to the left of the runway.
Injuries and Damage
The safety pilot and one student suffered minor impact trauma. The aircraft sustained severe damage to the landing gear doors, landing gears, both engine nacelles, engines, and fuselage, resulting in a hull loss. No other damage occurred.
Causal Factors
The investigation identified a combination of factors as the cause of the accident: (1) an intermittent malfunction of the Trimmable Horizontal Stabilizer Actuator (THSA) override mechanism, which led to loss of pitch control by both Elevator Aileron Computers (ELACs); this malfunction was due to the use of an inappropriate lubricating oil. (2) A design flaw in the Spoiler Elevator Computers (SECs) that allowed a single event—temporary dedecompression of the left landing gear—to cause loss of pitch control by both SECs.
Contributory Factors
The absence of ground spoilers arming for landing during touch-and-go training may have contributed to the temporary dedecompression of the left landing gear. Additionally, the aircraft maintenance documentation did not require any test of the override mechanism during regular maintenance checks, which could have allowed the wrong oil to remain unnoticed.
Conclusions
The Estonian Safety Investigation Bureau conducted the investigation in accordance with ICAO Annex 13 and EU Regulation 996/2010. The determined cause was a combination of the THSA override mechanism malfunction and the SEC design flaw.