The pilots of a Delta Air Lines flight did not notify authorities before dumping fuel on a populated part of Los Angeles, including several elementary schools, when it made an emergency landing at the city's airport, the Federal Aviation Administration said Wednesday.

Dozens of people were treated for skin irritation, but no serious injuries were immediately reported.

Flight 89, a Boeing 777, was en route to Shanghai from Los Angeles International Airport when it turned back because of an engine problem, the airline said.

The FAA said the crew of the flight did not tell air traffic control that they needed to dump fuel before returning to LAX and that it's investigating the issue.

Airplanes routinely dump fuel to reach a safe landing weight in the case of an emergency but this is usually done at higher altitudes and in more sparsely populated areas. After notifying air traffic controllers, the crew will be directed to an "appropriate fuel-dumping area," the FAA said.

"In this emergency situation, the fuel-dumping procedure did not occur at an optimal altitude that would have allowed the fuel to atomize properly," the FAA said in a statement.

Delta said that it sent crews to help local schools clean surfaces contaminated with fuel and that it shares "concerns regarding reported minor injuries to adults and children at a school in the area."