Dead Air

Dead Air is the third campaign in Left 4 Dead. The Survivors must make their way through Newburg to a runway in hope of catching a plane from Metro International Airport to get away from the Infected.

Below are walkthrough videos showing what to do on the 5 levels:

The Greenhouse

The Crane

The Construction Site

The Terminal

Runway Finale

Official description
Guide your team of Survivors out of the downtown core of Newburg's business district, through derelict office floors and still-inhabited cubicles, and out onto the runway of Metro International Airport, where the only thing standing between you and the last plane out of the city is a murderous army of the undead.

Graffiti
There are several instances on the rooftops where one may find writing, such as "help need food" or "S.O.S." There are also numerous writings about how a bomb will be dropped on the airport. Their predictions look to have come true when the Survivors enter the ruined facility. This is also mentioned in random dialogue by Survivors. Near the end of Runway Finale, sometimes the Survivors may state the airport was bombed to prevent the Infection from spreading. Also, near the sky way in The Terminal, Francis may say, "What idiot bombed the airport?"

However, it has been noted that the debris of a plane can be seen scattered through out the airport, leading to another scenario: That a plane crashed mid flight, and the bomb has yet to be dropped.

Players may also notice one of the later safe rooms with the writing "WE ARE THE REAL MONSTERS" on the wall, along with various other messages below it telling the writer that they are a moron, telling them that the Infected are the monsters, and somebody even tells them that he wishes that they are dead now. Beneath all of this, written in small letters, is a sentence that states "I miss the internet." Also in one sentence, it claims that the Infected were created by the military, and that there is a rumor that the government is giving a cure to the rich, followed by a claim that the virus was made by aliens, along with a writing saying "What if this was first contact?" followed by "What if your a moron?".

Several times throughout the campaign, the phrase "God is dead" can be seen. This was a statement originally made by the German philosopher Friedrich Nietzsche, and has heavily been quoted since. Occasionally, the Survivors may respond to the writings, saying things such as, "Oh, no! The zombies killed God!"

In the safe room of The Crane, there is some graffiti on the wall that states "This is our punishment." Right under this is the sentence "It's just Dead Air." - a reference to the title of the campaign.