On Sunday, a helicopter carrying Kobe Bryant, his daughter Gianna, and seven others crashed into a hillside near Calabasas, California. There were no survivors.

The Sikorsky S-76B was headed from John Wayne Airport in Orange County to the Mamba Sports Academy in Newbury Park, a facility that Bryant owned. No flight plan was filed.

There were low clouds and fog, and area police had grounded their own helicopters due to the weather. “Special VFR,” special visual flight rules clearance, was in place for at least part of the trip, meaning that the pilot needed to avoid the clouds and fog because he was flying using landmarks. This was atypical but not uncommon.

A spokesperson for the FAA explained to NPR that it is the pilot who is responsible for deciding whether to fly in bad weather, and whether to use visual flight rules or instrument flight rules (IFR), using instruments to navigate.

However, there was an aviation weather advisory at the time warning pilots that they would be required to use IFR due to poor visibility.

Now, the National Transportation Safety Board (NTSB) has taken the lead in the investigation, which was begun by local firefighters. A spokesperson for the agency explained that weather might be a factor in the crash, but that the investigation would be considering the pilot, the helicopter and environmental factors leading up to the crash. In other words, they will be looking for evidence of pilot error and/or a malfunction in the aircraft, in addition to the weather and any other environmental factors.

The pilot was apparently instrument-rated and licensed for helicopters. He was also a helicopter ground and flight instructor. The NTSB will be considering his flight history, the helicopter’s maintenance records and other records pertaining to the helicopter’s owner and operator.

There was no “black box” on this particular helicopter and none is required.

According to radio communications during the flight, the pilot was following freeways as a way to navigate. In his final transmission, the pilot told air traffic control that he was climbing to avoid a layer of clouds. The helicopter was traveling at between 120 and 160 knots before the crash, and then began to descend rapidly at a rate of more than 5,000 feet per minute.

The NTSB crew at the crash scene is currently gathering evidence rather than trying to determine a final cause of the crash. The cause likely won’t be available for several months.

Our thoughts go out to all those affected.