The helicopter that crashed last month in Califonia, killing Kobe Bryant and eight others, showed no signs of engine failure, the US National Transportation Safety Board said Friday.

The news comes as federal investigators continue to investigate the cause of the crash. The finding that the chopper didn’t lose power before the crash is one key conclusion, but many questions remain unanswered.

“Our investigators have already developed a substantial amount of evidence about the circumstances of this tragic crash,” said NTSB Chairman Robert L. Sumwalt in a statement. “And we are confident that we will be able to determine its cause as well as any factors that contributed to it so we can make safety recommendations to prevent accidents like this from occurring again.”

The report provided more details about the crash but not a definitive cause. That is likely to take several more months.

According to the report, the main impact crater was on a 34-degree slope and measured 7.5 metres by 3 metres in diameter and 60 centimetres deep.

“Examination of the main and tail rotor assemblies found damage consistent with powered rotation at the time of impact. The initial point of impact consisted of highly fragmented cabin and cockpit debris,” the report noted. The main wreckage was about 39 metres from the impact crater.

The engines were found lying inverted in the burned area. “Viewable sections of the engines showed no evidence of an uncontained or catastrophic internal failure,” the report noted.

Officials said the chopper, which was flying using only visual readings, slammed into a hillside amid extremely foggy conditions. A Los Angeles Times data analysis tracked the final moments of the flight, finding the helicopter flew dangerously close to another hillside just before crashing. The NTSB report said the chopper was destroyed by “impact forces and fire.”

The helicopter – a Sikorsky S-76 chopper built in 1991 – departed John Wayne Airport in Orange County at 9:06 am on January 26, according to publicly available flight records. The aircraft passed over Boyle Heights, near Dodger Stadium and circled over Glendale.

The pilot, Ara Zobayan, requested special visual flight rules, or VFR, which allow pilots to fly in controlled airspace when ceilings are less than 300 metres or when visibility is less than 5 kilometres. As weather deteriorated on the trip to Ventura County, the pilot requested “flight following,” a process in which controllers are in regular contact with an aircraft and can help navigate.

In recorded radio communications, the air traffic control tower is heard telling the pilot the chopper is too low for flight following. Radar data indicate Zobayan, who had been a licensed commercial helicopter pilot for 19 years, guided the copter to 700 metres and then began a left turn.

NTSB board member Jennifer Homendy said last week the helicopter, which lacked a terrain warning system, was at 700 metres feet when it lost communication with air traffic controllers. The helicopter was descending at more than 600 metres per minute at the time of impact.

The chopper hit the hillside at an elevation of 330 metres, about 6 to 9 metres below an outcropping. Even if the pilot had been able to fly above the hilltop, he would have faced new hazards, officials said.