Travelling west continuously to outrun the sun wouldn't be possible for an airliner jet. After a few hours, the sun would catch up (the plane going about 1/2 the speed of the sun, depending on the latitude). The better option would have been to fly to the winter hemisphere and get below the arctic or antarctic circle - which would give them - depending on the time of year - a day to 6 months of night, after which they could plan a route through the night side to the other hemisphere.
The aircraft is being loaded when the hijacker storms the plane and they immediately start departing. This wouldn't be possible as the aircraft would still be connected to ground services, cargo doors would be open, luggage loading, service carts fore & aft, etc.
Also the engines would not be running as a member of the flight crew is doing a walk around.
When Sylvie powers down the airplane's engines, all of the electronics on the plane would have switched off. Unless the battery power was engaged or the APU switched on.
At about 15:50 the pilot and Terenzio make a plan to head to Moscow. Departing from Brussels, this puts them 1390 miles to the East, the wrong direction. A few minutes later, they make a plan to head to Keflavik, 1330 miles West, the correct direction.
On the Equator, the terminator (line between night and day) moves at 1667 km/h (or Mach 1.3, while a Boeing 737 (which normally serves the Brussels-Moscow route) has a top speed of 946 km/h. But at higher latitudes the terminator moves more slowly, a point mentioned in dialogue. To stay ahead of sunrise they must keep above 55.4° latitude; Iceland, Moscow, and most of Alaska, Sweden and Scotland, for example, are north of that line.
At approximately 30:00, Sylvie says that the closest airport from Keflavik International Airport is in Northern Scotland. This is false. Even with the requirement of a 1500m runway, as stated by Mathieu, at least Reykjavik Airport, Húsavik Airport, Egilsstaðir Airport, Akureyri Airport, all in Iceland, and Vágar Airport in the Faroe Islands are closer. Egilsstaðir even functions as Keflavik's diversion airport.
The sporting event with dead bodies that is shown on TV at Brussels airport is apparently in Melbourne according to the TV news ticker. If the deadly phenomenon hit Australia before Europe's sunrise, then how did it hit Canada before the westbound travelers arrived? If Canada was hit first, the European public would have been well aware of the phenomenon hours before sunrise in Australia.
Twice the aircraft is seen from above, during the flight, but the same piece of land is shown below it.
The plane needs to avoid the sun, to do this at the equator, you'd have to fly 1.050 mph & 996 mph at latitude in Belgium. Commercial airliners can fly .85 of the speed of sound ~580 mph. It isn't possible for the plane to travel this fast and doesn't include landing, fueling.
In the opening minutes the NATO guy ,Terenzio's ,urgency is all wrong. Just before they depart the airport , a girl passenger was talking to friend in New York on phone who then died from the sun . If the sun had burnt New York then Brussels would have not long gone into nightfall (depending on the season of the year) and not be close to morning like Terenzio said. This would explain why they can fly west to Iceland and back east to Scotland in 5.5 hrs and still be dark.