Department of Homeland Security (search) Secretary Michael Chertoff has launched a review of last week's incident in Washington, D.C., in which a Cessna airplane flew into restricted airspace, forcing an evacuation of the White House and U.S. Capitol.

An official at DHS confirmed to FOX News on Wednesday that the "fairly routine" postmortem review will examine what role the Homeland Security Department plays and whether improvements can be made to determine the appropriate response to future potential threats.

North American Aerospace Air Defense (search), which operates in part out of the Pentagon, coordinated with air and homeland security officials at the National Capital Region Command Center (search), a combined security and law enforcement effort. The undertaking consists of officials from the Defense Department, Federal Aviation Administration, Transportation Security Administration, Customs and Border Control, Secret Service, U.S. Capitol Police and others.

Shortly after the plane entered the Air Defense Identification Zone (search) on May 11, NCRCC sprang into action. Secret Service raised the alert level at the White House to red, signifying that the plane was about three miles from the White House and four miles from the Capitol, which ultimately led to the evacuation of those federal buildings as well as the Supreme Court.

The review seeks to find out whether the mass evacuations of key buildings should have been called. One aviation source points to the size of the aircraft involved — a Cessna 150.

The source told FOX News that the plane model that flew over Washington is one of the smallest private aircraft around. The source said that with two people in the plane, "you'd be lucky to get a set of golf clubs on board," and suggested that with such a small payload, even if it had been packed with explosives the damage was unlikely to be significant.

Furthermore, the source said the F-16 and Blackhawk pilots who escorted the errant plane to Frederick, Md., where the Cessna pilot and his passenger were questioned and released, reported that they observed no hostile intent. The Cessna was tracked early on and identified as a plane from Pennsylvania. The source said nothing about the case fit the terrorist profile.

"It's a fair question for Secretary Chertoff to ask, given the size and the speed, [whether] that plane may have been incapable of generating a lot of damage," the source said.

A security source also told FOX News that questions are being asked whether it was wise to evacuate because thousands of people were left exposed on the sidewalk. In a different scenario, for instance, if a terrorist had been at the wheel and the plane had been carrying chemical or biological agents, the evacuation would have created a better opportunity to exact damages.

FOX News has also obtained the text message about the incident, sent by DHS to local officials. A source close to D.C. Mayor Anthony Williams (search) said the mayor was not officially notified of the suspected threat until 12:23 p.m. — three minutes after the incident was declared over and the Secret Service security alert level returned to its usual yellow status.

The text message appears to reference the wall-to-wall coverage on television and radio news stations.

"You are probably following along the news — we had an unauthorized aircraft in NCR airspace. WH (White House), Capitol, Supreme Court were evacuated. Air assets scrambled and launched. As of 12:20, all clear has been given. Evacuation of facilities over," the text message read.

A source close to the mayor told FOX News that Williams met with Chertoff on Tuesday to discuss the incident and the communication problems, including D.C. emergency services' not being notified in a timely manner.

FOX News' Catherine Herridge contributed to this report.