What a difference two decades makes. 

As Iraq assumes total control over its borders and security following the U.S. withdrawal, the U.S. Air Force must now ask permission in order to fly over Iraqi airspace. 

The change is one the United States is adjusting to, after having virtual free reign over the Iraqi skies for the last two decades -- first in support of no-fly zones following the Persian Gulf War and later in support of the Iraq war

However, it comes as no surprise. 

"As is the case for any sovereign country, U.S. aircraft need permission to transit Iraqi airspace," Maj. Chad Steffey, an Air Force spokesman, told FoxNews.com in an email. 

The United States not only must seek permission but transit through quickly -- according to a statement from U.S. Transportation Command, Iraq requires prior notice of eight business days in order "to coordinate a diplomatic clearance." That clearance is then valid for 24 hours. 

"Once that time expires, coordination of a new clearance is necessary," the statement said, describing the lead time required as similar to that of other nations. 

According to a report in the Air Force Times, one medical evacuation flight was postponed because it used up its allotted time just trying to seek permission. 

The Air Force reportedly is trying to reduce the amount of time it takes to receive the clearance. 

According to an Iraqi government spokesman, Iraq has not yet denied any request by the U.S. to use the airspace. 

"It is normal that the United States needs to ask permission as they ask any other country that they are crossing through, keeping in mind that we have agreed that Iraqi airspace -- as with the land or water -- should not be used for any attack against any other neighbors," Ali al-Dabbagh told the Air Force Times.

However, the Transportation Command statement said the U.S. "has experienced a few limited denials for requests made outside the stated requirements."