Los Angeles (CNN) A day after a Delta Air Lines plane dumped jet fuel over several Los Angeles schools , federal authorities said the pilots of Delta Flight 89 did not ask for approval to release the fuel as part of their emergency landing.

Air crews will typically notify air traffic control of an emergency and indicate they need to dump fuel, the Federal Aviation Administration said. Air traffic controllers direct the plane to the appropriate fuel-dumping area.

"A review of yesterday's air traffic control communications shows the Delta Flight 89 crew did not tell air traffic control that they needed to dump fuel," the FAA said in a statement.

Delta spokesman Adrian Gee said the airline didn't have comment because the investigation is ongoing.

According to the audio of the conversation between a Delta pilot and an air traffic controller, posted on the website LiveATC.net , the pilot said the flight would return to Los Angeles International Airport because one engine had compressor stalls.

Pilot: "We've got it back under control. We're going to come back to LAX. We're not critical. We're going to slow to 280 knots, and uh, why don't you point us downwind at 8,000 feet (unintelligible) and we'll turn back to LA."

Tower: "OK, so you don't need to hold or dump fuel or anything like that?"

Pilot: "Uh, negative."

The FAA also said the fuel dumping procedure did not occur at the optimal altitude that would have allowed the fuel to atomize properly.

Fire crews treated 60 people after the fuel fell over five elementary schools and one high school Tuesday, said inspector Sean Ferguson of the Los Angeles County Fire Department.

Children at six schools were affected by the fuel dump.

Did this have to happen?

The Boeing 777-200 was headed to Shanghai, China, Delta said. It had 181 people on board, according to radio traffic.

"The aircraft landed safely after a release of fuel, which was required as part of normal procedure to reach a safe landing weight," the airline said.

There are maximum takeoff and landing weights for aircraft, so for a plane with full fuel tanks to land, it must dump the fuel to avoid potentially crashing upon landing, said CNN aviation safety analyst David Soucie.

After hearing the transmissions between the tower and the pilot, Soucie said, "The situation is a failure to communicate." The air traffic controller should have asked the question about holding or dumping fuel without using the word "don't," and he should have repeated the questions, Soucie said.

The pilot said the engine was under control so he could have taken the plane over the Pacific Ocean to dump fuel or burn it off, Soucie, a former FAA safety inspector, said.

Soucie said the pilots might have forgotten to dump the fuel until the final approach while doing a pre-landing checklist and discovered the weight of the plane was too heavy. And rather than go around the airport again to drop elsewhere, they might have decided to dump it over land.

According to the FAA, which is investigating Tuesday's incident, there are special fuel-dumping procedures for aircraft operating into and out of major US airports.

"These procedures call for fuel to be dumped over designated unpopulated areas, typically at higher altitudes so the fuel atomizes and disperses before it reaches the ground," according to the FAA.

Had the plane been at 8,000 feet when the dump occurred, the fuel would never have hit the schools because it would be atomized after leaving the wings, Soucie said.

It is "very rare (fuel is dumped) at a lower altitude where it reaches the ground," he said.

Fuel has evaporated

Those doused by the jet fuel were decontaminated with soap and water and did not need to be hospitalized, said Sgt. Rudy Perez of the Los Angeles School Police Department.

Officials said Wednesday it was safe for children to return to the schools affected by the jet fuel.

The children changed from their clothes and wore gowns.

Park Avenue Elementary fifth grader Justin Guiti said the fuel sprayed all over him and got into his eye.

"Drops of water were coming down. I thought it was a rainbow, and I looked up and it was gasoline," he said.

Miguel Cervantes, a sixth grader, said his skin itched afterward.

"I thought it was smoke, but when it went down, I felt it and it smelled like gas," he said.

The affected schools had normal schedules Wednesday. All the jet fuel has since evaporated, the fire department said.

"With the monitoring devices that we have, there are no explosive limits that are being detected at all, as well as solid or liquid products remaining," Los Angeles County Fire Department Battalion Chief Jason Robertson said.