What does the runway controller do to prevent take off?

The correct answer indicates that firing a red cartridge is the method used by a runway controller to prevent takeoff. This action serves as a highly visible and immediate signal to pilots that they must abort their takeoff. The red cartridge produces a loud noise and a noticeable flash, ensuring it captures the attention of anyone involved in aircraft operations on or near the runway. This method is particularly effective in ensuring safety in critical situations where immediate attention is necessary.

Other methods, while also part of the communication arsenal for runway controllers, do not provide the same level of immediacy or visibility. For instance, a warning siren or flashing red lamp are more passive forms of signaling and may not be as effective in all scenarios. A warning banner, while noticeable, may not have the same urgency or immediacy as the rapid and stark signal produced by firing a red cartridge. Therefore, the use of a red cartridge showcases the importance of swift, decisive action in maintaining safe runway operations.