The Houston Fire Department shared images of the destruction caused by a helicopter crash in the city's Second Ward Sunday night.
CNN  — 

Lighting on a Houston radio tower reportedly failed just days before it was hit by a helicopter on Sunday, killing four people in a fiery explosion that toppled the tower and left debris scattered through the neighborhood.

Operating as an air tour flight, the helicopter was flying at an altitude of 600 feet when it slammed into the 1,000-foot-high tower just before 8 p.m. Sunday, according to open-source data and investigating officials.

The tower’s lights were “unserviceable” until the end of the month, according to a Federal Aviation Administration notice to pilots published last Thursday.

Towers higher than 200 feet above ground level “should normally be marked and/or lighted,” and any tower lighting outage “should be corrected as soon as possible,” according to FAA guidance published in 2020.

Towers and guy wires pose a unique hazard to helicopters, which typically fly at low altitudes and can be especially difficult for pilots to spot at night. Video of the crash shows at least one flashing light at the very top of the tower but the rest of the tower does not appear to be illuminated.

The crash ignited a large explosion near Engelke Street and North Ennis Street that could be heard at a fire station nearly half a mile from the site, Houston Mayor John Whitmire said during a late-night news conference.

The crash killed all four people, including a child, on board the privately owned Robinson R44 helicopter, according to Houston Police Chief Noe Diaz and federal officials. The pilot and three passengers were killed, according to the FAA.

NTSB investigators are planning to assess and recover the helicopter at the crash site.

While the cause of the crash remains unclear, National Transportation Safety Board officials are expected at the crash site Monday to examine and recover the aircraft, the agency told CNN. Law enforcement officials are looking for debris across the area and the Houston Police Department’s vehicular crimes division is making a three-dimensional scan over a 4-acre area to share with the NTSB and the FAA, Lt. Jonathan French said in a news conference Monday.

Additional investigators from NTSB will arrive at the scene Monday evening, where they will continue to work for at least another day, said Brian Rutt, an air safety investigator with NTSB.

The aircraft departed Ellington Airport, which is about 17 miles south of the crash site. Rutt said the helicopter did not have a flight data recorder, which is not required.

The flight was categorized as “sight seeing” and the helicopter is registered to Porter Equipment Holdings LLC of Magnolia, Texas, according to the FAA. CNN is reaching out to the company for comment.

Surveillance video from a nearby home obtained by CNN shows what appears to be the helicopter flying toward the tower, then exploding on collision, lighting up the sky.

Witness video shows fire personnel urging onlookers to clear the area where a fire was burning and warning them of a nearby gas tank.

“This is a tragic event tonight. It’s a tragic loss of life,” Diaz said.

Officials advised residents who see human remains around the crash site to leave the area alone and report it to authorities.

The mayor said the city is “fortunate” the explosion was not more severe because there is a gas tank in the area.

Lawrence Gurule was watching a football game on Sunday night when he heard a noise that “sounded like a bomb.”

“I ran outside and looked up and I could see smoke. The tower was gone,” he said.

Manuel Arciniega was nearby when the crash occurred, he told CNN affiliate KPRC. “My buddy behind me told me to look up in the sky, and I just saw the cell tower crumbling down. They said a helicopter hit it.”

“It will be a large investigation because of the expanse of the accident,” Diaz said. If residents find helicopter parts in the area, they should avoid touching them and notify fire or police officials, he added.

CNN’s Lauren Mascarenhas, Rosa Flores and Sara Weisfeldt contributed to this report.