Auxiliary take-off boosters igniting.
Close-up of the rockets!
SE <<FWOOOOSH>>
UrsusArctos: For military nerds out there, the Eva transporter looks like a scaled-up Northrop XB-49, a jet-powered flying wing from the late 1940s/early 1950s. Rocket-assisted takeoff (RATO) was used during the turbojet era, but it fell out of service because modern turbofan engines generate their maximum thrust at sea level.
Additional Commentary
ath: Wait, wasn't Northrop's aircraft called YB-49? If I remember correctly, the 'Y' prefix designates a prototype of an aircraft intended for production, while the 'X' prefix is reserved for purely experimental aircrafts. That said, the distinction can be a little fuzzy at times (compare YF-22/YF-23 to X-32/X-35, for example).
The Evangelion Encyclopedia seems to be confused on this point. It notes the resemblance to a real aircraft they call "XB-49" but seems surprisingly sure that the official designation of this aircraft in the Evangelion universe is "YB-49". Does any official source confirm this?