It is too early to draw any conclusions. As the crash happened shortly after take off, investigators will look at a range of possibilities that include a possible bird strike (as happened to US Airways flight 1549, also known as "the miracle on the Hudson" in 2009) or any other kind of "foreign object ingestion" into the engines.
They will also consider whether one of the two CFM56 engines suffered an uncontained failure, such as that which killed a Southwest Airlines passenger on a flight in 2018.
Any plane crash will also be analysed for the possible effects of weather, human interference or pilot error – though there were three highly experienced captains and a first officer on board.At present that seems extremely unlikely. The Max is the successor to the 737-800. But the older jet does not have the “anti-stall software” known as MCAS, which was implicated in the losses of Lion Air and Ethiopian Airlines Boeing 737 Max crashes in which 346 people died.
UIA was created after the collapse of the Soviet Union and Ukraine’s independence, and is the national carrier. But it is struggling financially. One reason is that it cannot use Russian airspace and is excluded from Crimea, the Ukrainian territory currently occupied by Russia. This prohibition reduces its potential route network and extends many journey times.
It is also facing intense competition from budget airlines, in particular Wizz Air and Ryanair.
In response the airline’s business model changed three months ago to exploit the “hub-and-spoke” network. Many of the passengers on the doomed flight would be intending to change planes to destinations in western Europe, including London Gatwick.