What happened
The Russian Su-24, an all-weather attack aircraft, was shot down by Turkish F-16s in the Turkey-Syria border area on 24 November 2015.
The plane crashed in the mountainous Jabal Turkmen area of the Syrian province of Latakia, killing the pilot.
A Russian marine involved in a helicopter rescue attempt was killed when the helicopter came under fire.
The navigator in the jet, Capt Konstantin Murakhtin, survived the crash and was taken to Russia's Hmeimim airbase in Latakia by Syrian government forces.
Turkey said planes were warned 10 times during five minutes via an "emergency" channel and asked to change direction.
The Russian defence ministry insisted that the aircraft remained within Syria's borders throughout its mission and did not violate Turkish airspace and received no warnings.
Strained relations
The incident strained relations between Moscow and Ankara, with Mr Putin saying he had been "stabbed in the back".
The Russian leader also accused Mr Erdogan of collaborating with so-called Islamic State.
Russia hit Turkey with a raft of sanctions, banning import of Turkish foodstuffs and stopping Russian package holidays to Turkey.
Mr Erdogan offered to meet Mr Putin in person but Moscow refused and the pair have not spoken to each other since.
---------------------------------------------------
Russia and Turkey were already at a state of alert. Both were already militarizing in preparation for a conflict.
