Factual error: The call sign used for the AC-130 is "Spooky" which is the AC-130U nickname. The plane in the scene is an AC-130H "Spectre" as evidenced by the "cheeks" on the plane and the logo visible in the shot where the aircraft rolls in. No gunship would fly using the nickname of another type of aircraft as its callsign, too much potential for confusion.
Factual error: When Barricade interrogates Sam, he asks him if he is "Username ladiesman217" and "Where is eBay item 21153". However, it is impossible for an item sold so recently to be that item number. If you sell an item now, it would be over item number 200000000000.
Continuity mistake: In the scene where Sam and Mikaela are looking at Bumblebee's engine, both of Bumblebee's doors are open when Mikaela starts walking away. Sam jumps in the car and pleads with it to start, and the shot changes to side view from passenger side of him trying to start. Here both doors are open as well. But when the shot changes to Bumblebee starting up and Sam jumps out to close the hood, the passenger door is suddenly closed.
Continuity mistake: Before Barricade interrogates Sam, the Decepticon throws Sam on the windshield of a car, and a wheel falls off the car's roof, but then reappears back on the roof in a following shot.
Continuity mistake: The number of the surviving ranger team changes, as Keller announces the base attack a shot is showed of 8 rangers and Mahfouz (the young boy), then as the team is attacked by Scorponok one team member is killed, but seconds later as the team runs down a dune they are still 8 rangers. One runs past the camera quickly while 7 and Mahfouz comes down the dune, later as Epps directs the air support he claims they are only 7 rangers, and as the Huey lands there are only 7 rangers.
Revealing mistake: Near the beginning Shia and Megan Fox are driving in Bumblebee, before it breaks down. There is no road shown in this entire scene, no matter which angle you see. No landscape either. This indicates the scene was probably shot on a soundstage and the car was not moving. It is also obvious there is no wind coming in through the windows.
Continuity mistake: When Sam is on the roof, the streets below appear normal, but when Megatron hits the building and Sam falls, there is destruction on the streets.
Continuity mistake: When one of the Autobots knocks out the power transformer at the Witwicky house the lights all go out, however in following shots the lights in the house have all come back on again.
Revealing mistake: When Optimus Prime is powersliding into the city, right before he transforms, you can see that the truck is actually a CGI replica, because the blue is much lighter than it was a second ago, when he already burst out of the shadow of the alley.
Continuity mistake: When Epps and Lennox spot Starscream thinking he's Air Force, Epps is holding the mic up to his mouth with his right hand and says, "Raptor, Raptor, do you copy?" Next shot, however, the mic is being held up in his left hand.
Character mistake: Sam says that Archibald Witwicky explored the Arctic Circle in 1897. But when Frenzy finds the article, it is dated 1895.
Answer: Because the Decepticons didn't know where Megatron ended up for the last 100 years. Bumblebee arrived on Earth as a scout to check out for any clues, found the glasses on Ebay, signalled the other Autobots, which prompted Blackout and Frenzy to investigate the base in Qatar, which lead to Blackout downloading the base computers and Frenzy hacking the computers aboard the aircraft later leading to the discovery of Megatron's whereabouts.
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