The room they were inside was an air friction endurance testing area. When fighters travelled above the speed of sound, they received a huge amount of air friction. The surface temperature would reach a few hundred degrees. That facility was used to see if the craft could endure that friction. As they could not create air moving at the speed of sound, the room artificially created a special type of strong wind by using a large amount of iron sand to increase the friction like a file.
Hamazura was protected by the cockpit model.
Mugino did not have that protection.
A tremendous noise split the air as the 100 meter square room was filled with explosive wind that created friction of a few hundred degrees. Mugino could move at high speed like a rocket engine, but she couldn’t escape when the entire area was filled up like that. She was knocked back as if she had been hit by a giant fly swatter and she struck the other wall.

[…]

A huge beam of light shot across and blew the tractor to the side. Before Hamazura could think about what that beam of light had been, the electromagnetic catapult shot the plane into the sloped tunnel leading to the surface. The passenger plane Hamazura and Takitsubo were aboard shot into the night sky as if it had been a paper airplane thrown by a giant hand.
Hamazura made sure not to touch the controls.
The autopilot program slowly leveled out the aircraft. As long as they didn’t run into any turbulence, they should be fine.
(Mugino…)
That beam of light had most likely been her. He didn’t know what she had fired that beam for, but he had a feeling he would meet her again somewhere.

Toaru Majutsu no Index vol.19 ch.4 pt.4