By Joanna Plucinska, Gleb Stolyarov and Nailia Bagirova

(Reuters) - A passenger jet operated by Azerbaijan Airlines crashed near the city of Aktau in Kazakhstan on Wednesday, after diverting from an area of southern Russia where Moscow has repeatedly used air defence systems against Ukrainian attack drones. 

At least 38 people were killed while 29 survived.     

Here is what we know so far:

WHAT HAPPENED?

Azerbaijan Airlines flight J2-8243 from Azerbaijan's capital Baku flew hundreds of miles off its scheduled route to Grozny, in Russia's southern Chechnya region, and crashed on the opposite shore of the Caspian Sea around 3 km (1.8 miles) from Aktau in Kazakhstan.

It is not known why the plane veered off hundreds of miles across the Caspian Sea. 

Russia's aviation watchdog said on Friday the plane had decided to reroute from its original destination amid dense fog and a local alert over Ukrainian drones.

WHAT CAUSED THE CRASH?

This is not yet known as an official investigation gets underway.

Four sources with knowledge of the preliminary findings of Azerbaijan's investigation told Reuters on Thursday that Russian air defences had mistakenly shot it down. Pictures of the plane wreckage showed what appeared to be shrapnel damage to the tail section of the plane. 

Kremlin spokesman Dmitry Peskov said on Friday he had nothing to add and did not want to give any assessments until the official investigation made its conclusions.

Russia's aviation watchdog said on Wednesday the emergency may have been caused by a bird strike. Russia has said it is important to wait for the official investigation to finish its work to understand what happened.

On Friday, Azerbaijan Airlines said preliminary results of an investigation showed the plane experienced "external physical and technical interference", without giving details. 

Two passengers on the plane told Reuters that there was at least one loud bang as it approached its original destination Grozny.

INVESTIGATION

Kazakhstan is leading the investigation which will be carried out under international rules known throughout the industry by their legal name "Annex 13", governed by the United Nations aviation body ICAO.

The plane's black box, which contains flight data to help determine the cause of a crash, had been found, Interfax reported on Wednesday.

The governments of passengers and crew on board - Azeri, Kazakh, Russian and Kyrgyz - and Brazil, which is home of the planemaker Embraer will likely be involved. The United States, where the plane's engine was made, may also participate.

Brazil sent three Air Force investigators to Kazakhstan to take part in the probe. Embraer representatives are also on the ground, according to Kazakhstan's president, local media reported.

Under Annex 13 guidelines, a preliminary report will be published within 30 days of the incident and a final report within 12 months.

The final report on the accidental downing of a jet in Iran took over a year to be released by Iran's civil aviation body.  

IS THERE A PRECEDENT FOR THIS KIND OF INCIDENT?

If confirmed, it would be the third major fatal downing of a passenger jet linked to armed conflict since 2014, according to the Flight Safety Foundation's Aviation Safety Network, a global database of accidents and incidents.  

Previous disasters include the shooting down of Ukraine International Airlines Flight PS752 in 2020 by Iran's Revolutionary Guards, killing all 176 people on board.

In 2014, Malaysian Airlines Flight MH17 was shot down over eastern Ukraine by a Russian BUK missile system with the loss of 298 passengers and crew.

IMPACT ON AIRLINES' OPERATIONS

Azerbaijan's civil aviation body said flights from Baku to Russia would be suspended for safety reasons until the release of the final report. Flydubai has suspended flights to two southern Russian airports since the crash. 

(Reporting by Joanna Plucinska in London, Gleb Stolyarov in Tbilisi and Nailia Bagirova in Baku; Editing by Josephine Mason and Ros Russell)