It’s the second day of investigation into Wednesday’s Ukraine International Airlines plane crash, which killed all 176 people on board when the Boeing 737 plunged to the ground just after takeoff from Tehran.
Questions on what caused the tragic incident loom large. Here are some of them:
Why did the plane crash?
There have been conflicting reasons given for the tragedy, and Ukrainian authorities have signaled that an answer will only be provided after a full investigation has been made.
By Thursday, the Iranian Civil Aviation Organization released a preliminary report that said the plane was on fire before it crashed, citing witnesses. It added that the aircraft changed direction after a problem and turned back toward the airport.
Now, Ukraine says multiple possible theories are being discussed with Iranian investigators: including the plane being hit by an anti-aircraft missile, a collision, technical failure or a terrorist act.
Is it linked to Boeing’s ongoing technical problems?
The plane is a Boeing 737-800, a predecessor to the company’s 737 Max, which has been grounded since March after its involvement in two fatal crashes that killed 346 people.
But the 800 version of the jet, also known as a 737 Next Generation or NG, has had its own problems.
All of this could add to the crisis Boeing has been grappling with over the different jet, the 737 Max, but there has been no indication yet that this is a manufacturing issue.
What will happen to the black box?
A plane’s so-called “black boxes” – the flight data and cockpit voice recorders – can provide crucial evidence about what happened before a crash.
Iran’s Civil Aviation Organization head, Ali Abedzadeh, said it would not hand the flight data recorders to Boeing or the United States after they were found on Wednesday.
What is unclear is whether that decision was to do with hostilities between Tehran and Washington, which escalated after a US strike that killed Iran’s top commander, Qasem Soleimani, on Iraqi soil last week.
The move was not necessarily against protocol, former US FAA chief of staff Michael Goldfarb told CNN Wednesday.
Under international rules, Iran would be the lead investigator of the crash and Ukraine should participate as the state of registry and state of operator of the aircraft.
But the US – where the Boeing jet was designed and manufactured – is not required to be involved in investigations right off the bat, Goldfarb said.
But Goldfarb added there was no way the Iranians could refuse to work with Boeing and do justice to the investigation.
“They have to work with Boeing. Boeing has all the data, owns all the drawings and designs, they have the engineers, they know the plane.”
This does not mean there has been no global cooperation. Canada and Sweden were invited to join the investigation on Thursday by Iranian and Ukrainian experts.