Officials at the Birmingham-Shuttlesworth International Airport removed the panel a day after a sign fell on Luke Bresette, of Overland Park, Kan., killing him.
His mother was severely injured and two of his siblings were also hospitalized. The children were being treated at Children's of Alabama. Their mother, Heather Bresette, was taken to University Hospital, where spokeswoman Nicole Wyatt said she is in critical condition.
Firefighters estimated the panel, which displayed arrival and departure times, weighed 300 to 400 pounds. It was located in a recently renovated terminal that includes two concourses.
The airport completed the first phase of a more than $201 million modernization effort and opened newly renovated concourses about a week ago.
Mayor William Bell said he talked with the boy's father - who was not injured - and is pressing officials to explain how the sign toppled over.
"I cannot come close to understanding his heartache. But I will get answers. I'm calling on the airport authority to thoroughly investigate this horrible incident. I want a full report on my desk as quickly as possible," he told AL.com.
Airport officials met Saturday, but would not elaborate on other safety measures being taken.
"President and CEO Al Denson and the staff are continuing to work with officials to investigate. This includes discussions with contractors and subcontractors responsible for the modernization," Chairwoman of the Airport Authority Board of Directors Gaynell Hendricks said in a statement. The contractors and subcontractors were not identified.
Airport spokeswoman Toni Herrera-Bast said officials aren't sure how the sign fell. The airport continued operating while rescue workers tended to the family.