A medical transport plane struck power lines in cloudy weather before it crashed last month near San Diego, killing two flight nurses and two pilots, federal investigators said Tuesday.

The Learjet 35A crashed on Dec. 27 while preparing to land at Gillespie Field in El Cajon, according to a preliminary report from the National Transportation Safety Board.

The weather was overcast with clouds and mist when the plane struck power lines and then crashed into the yard of a home in the unincorporated San Diego County area about 1.5 miles (2.4 kilometers) east of the runway, the report said.

The report didn’t indicate the exact cause of the accident, which will await the final report.

Nobody on the ground was hurt.

The crash killed pilots Douglas Grande, 42, and Julian Bugaj, 67, and flight nurses Christina Ward, 52, and Laurie Gentz, 68. They worked for Aeromedevac Air Ambulance, according to the El Cajon-based company.

The twin-engine jet was registered to El Cajon-based Med Jet LLC, according to Federal Aviation Administration records.

The plane had flown that day from Lake Havasu in Arizona to Orange County, south of Los Angeles, for a patient transfer and was heading back to its home base at Gillespie Field when it went down, the NTSB report said.

Radio communications between the jet and the airfield showed that the pilot canceled an instrument flight rules approach to one runway and requested a switch to another runway using visual flight rules.

After the switch was granted and new instructions were given, the pilot asked that the field lights be turned up and was told they were already at 100%.

The report indicated that plane overflew the airport at low altitude and did not significantly climb while turning to reapproach the field.

Just before the crash, the pilot suddenly exclaimed three times and screamed, according to communications recorded by LiveATC.net.