Airstrike

An airstrike is a term used to describe a military strike (single, limited attack on an enemy position) conducted by combat aircraft using ordnance such as missiles, machine guns, and bombs. Airstrikes are usually coordinated by friendly ground units on (confirmed or suspected) enemy ground positions.

In game
In Call of Duty 4: Modern Warfare multiplayer, players who achieve a five-kill streak (killing five enemy players consecutively without dying) are given the ability to call in an airstrike. Airstrikes cannot be called in while another airstrike is in progress, regardless if the the Airstrike were called by their teammates or their enemies. Airstrikes will not damage or destroy helicopters. When the player calls in an airstrike, they must select the target area. The aircraft will fly in from the direction of the current spawn area of the players team and deploy explosives in a line, although the bombs will damage enemies outside the line of attack. In multiplayer airstrikes are delivered by 3 F-15E Strike Eagles for the Marines/SAS or by 3 MiG-29 'Fulcrums' for the OpFor/Spetsnatz, though in the SAS mission Heat, airstrikes are delivered by USMC AV-8 Harrier jump jets. Airstrikes are capable of penetrating thin material such as metal sheets and drywall. Airstrikes are also non-stackable; a player's airstrike option will be replaced by a helicopter support option if the player gets 2 more kills without dying and without using the airstrike option.

Multiplayer Tactics
On maps with mostly indoor areas or many buildings, airstrikes are best used on the most exposed and open areas of the map. It is recommended that, in cases where the enemy positions are known, that players lead the targets, as the air strikes take a while to arrive and thus could miss a target that was in the center of the reticule during the aiming stage. On maps where there is little cover, like Bog and Shipment, airstrikes can kill many enemies.

When your UAV is activated and pinpointing your enemies' location(s), call in an airstrike at or near that location so you can catch most of them in the attack.

It is helpful when playing Search and Destroy to save your airstrike until you change back to the defense side. That way, you can quickly call in an airstrike when the round starts and catch the enemy off-guard.

Keep in mind that when the enemy calls in an airstrike, there is NO voice warning of an inbound strike. This means that if you hear jets but no message of any kind try to find some overhead cover, especially when you are surrounded by friendlies.

If you look around the area after an airstrike, you can find cluster bomb casings, presumably belonging to CBU-87 Cluster Bombs.

Glitches
It is possible to cause a glitch in the multiplayer game where multiple airstrikes are called in simultaneously. This happens when two or more players use airstrikes at the exact same instant, although the timing must be so precise that it rarely occurs. It is also possible to be in the middle of an airstrike and not be hit by the first two bombings, and then sometimes be instantly killed by the third. Players inside buildings may also be killed by airstrikes, seemingly "magically," even if there is no hole in the roof or door to the outside nearby. This usually happens with players standing near outside walls in buildings.

An airstrike can also glitch and fly along the ground and bomb underneath the map, specifically on the Countdown map, this happens when you call it in on one of the empty missile silos. The game reads this as the floor of the map and so the planes fly at the height of the actual map, the bombs doing no damage.