TIMELINE: U.S. helicopter crashes in Iraq

(Reuters) - Two U.S. military personnel were killed when their helicopter came down under enemy fire north of Baghdad, the U.S. military said on Tuesday.

At least nine helicopters have come down in 2007, killing 30 people, mainly American soldiers.

Following is a list of major incidents in Iraq involving helicopters this year.

January 20, 2007 - U.S. Black Hawk shot down northeast of Baghdad, killing all 12 aboard.

January 23 - Blackwater security contractors in two helicopters attacked in Baghdad. One shot down, killing all four aboard. A fifth contractor is shot dead aboard the second helicopter.

January 28 - U.S. Apache shot down north of Najaf, killing two crew.

January 31 - A Blackwater helicopter makes hard landing south of Baghdad after being brought down by ground fire.

February 2 - U.S. Apache shot down northwest of Baghdad, killing two crew.

February 7 - A U.S. Sea Knight is shot down by a missile northwest of Baghdad, killing seven U.S. military personnel aboard. The U.S. said a sophisticated piece of weaponry was used. The Islamic State in Iraq claims responsibility.

February 11 - U.S. military says a second Black Hawk helicopter has been shot down since January 20 but gives no date for the incident. It says there were no injuries and the helicopter returned to service.

February 21 - Insurgents shoot down a Black Hawk U.S. military helicopter with nine people on board north of Baghdad but no one is killed in the eighth downing of a helicopter.

May 28 - A U.S. helicopter comes down under enemy fire in Diyala province, north of Baghdad killing two U.S. military personnel. Six more died when a column of vehicles heading to the crash site was ambushed.

NOTES: Details of some U.S. military helicopters:

Apache - Two crew; missile-firing main attack helicopter.

Black Hawk - At least three crew; frontline helicopter, carries 11 combat troops into action; also medical evacuation.

Chinook - Two crew; can carry up to 55 passengers or cargo; twin-engine, tandem-rotor, heavy-lift transport helicopter. The twin-rotor Sea Knight, the Marine version of the Chinook, can carry up to 25 passengers and four crew.