• A sightseeing helicopter crashed into a radio tower in Houston on October 20, killing the pilot and three passengers.
• The NTSB said in a preliminary report that transmission between the helicopter pilot and air traffic stopped suddenly moments before the fatal crash.
• The tower’s top and middle lights were flashing as the helicopter headed toward the tower, according to the report

The pilot of a helicopter that crashed into a radio tower in Houston on October 20killing all four people on board, was in contact with air traffic control moments before tragedy struck, officials said.

According to a preliminary National Transportation Safety Board (NTSB) report obtained by PEOPLE and issued nearly two weeks after the incident, the pilot of the Robinson R44 helicopter, later identified as Samantha Grandbouchewas talking to the air traffic controller and asked for the “downtown loop”.

Then, a few minutes later, the air traffic controller issued a traffic warning for the company’s tour helicopter, the report said, with Grandbouche acknowledging that there was traffic visible through it. Automatic Broadcast Dependent Surveillance.

“The controller asked the accident pilot to maintain visual separation from traffic and the pilot was reading instructions when the radio transmission abruptly ended. No further communications were received from the accident helicopter.”

The helicopter, which departed Houston’s Ellington Airport for a sightseeing tour, crashed into the tower about 100 feet from the top of the 1,003-foot radio tower, the report added. According to surveillance footage, the tower’s top and middle beacons were flashing as the helicopter headed toward the tower.

“During impact with the radio tower, an explosion occurred and the helicopter fell to the ground,” the NTSB’s preliminary findings said. “The radio tower collapsed onto the helicopter, and a post-impact fire destroyed the helicopter.”

In addition to Grandbouche, the three passengers killed in the crash were family members Julio Cesar Lerma, Marie Alonso and Dylon Lerma, according to the Harris County Institute of Forensic Sciences, CBS affiliate KHOU reported.

PEOPLE has reached out to the Harris County Institute of Forensic Sciences for comment.

The NTSB report also stated that the debris field contained sections of “plexiglas, main rotor blades, console components, upholstery, flight controls and landing gear.” Parts of the forward fuselage were stuck in the tower “about 100 feet up.”

The report’s findings did not indicate what caused the accident. A final report is expected to be issued in 18 to 24 months, the Associated Press reported.

Garrett Kauffman, a friend of Julio Cesar Lerma, one of the four people killed aboard the helicopter, remembered Lerma as a home remodeling worker.

“He always came to the rescue,” Kauffman said KHOU. “He just said, ‘OK, yeah, we can do that, we can figure it out.’ He was a true friend.”

Lerma was the father of three sons, Kauffman said, relatives said Dylon Lerma, who also died in the crash, was Lerma’s youngest son, KHOU reported.

“I think he lived life to the fullest,” Kauffman added of his friend. “I think he would, like I said, do anything for these guys. A total professional, always, and he will be missed. I miss him every day.”

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Ronnie Zepeda, a longtime neighbor of Lerman’s, said ABC affiliate KTRK that he saw Lerman just a few hours before the incident.

“Him and his little boy, they were here,” Zepeda said. “The little boy was running around.”

Zepeda later said fondly of Lerman: “He was a very good gentleman. He was a very good human being. An exceptional neighbor. I loved him. I loved him very much.”

A GoFundMe was launched to raise money for Lerma’s older surviving sons.

Meanwhile, the Houston law firm Sorrels Law said it is representing Lerma’s family members and the two other passengers killed in the crash and is filing a lawsuit on their behalf against Grandbouche, the owner of the radio tower and helicopter company. NBC affiliate KPRC reported.

“Our clients deserve answers and we are determined to uncover the truth about what led to this tragedy,” attorney Randy Sorrels said in a statement. Facebook post Friday, November 1. “By seeking accountability, we hope to prevent future accidents and bring some peace to the families who have endured so much loss.”

The people contacted National Helicopter Solutions, the helicopter company, and SBA Communications, the owner of the radio tower, who were named in the lawsuit on Nov. 1.