INDIANAPOLIS – The pilot of a small plane that crashed in southeast Indiana was navigating by onboard instruments in foggy, misty conditions when it plowed into a field, killing him and three passengers, a preliminary federal report shows.

Wednesday’s report from the National Transportation Safety Board states that weather conditions were so poor at the time of the Dec. 2 crash that a pilot on a similar flight path diverted away from Greensburg and landed safely at another southern Indiana airport.

According to the report, witnesses also told investigators that pilot-activated runway lights were not illuminated when Donald Horan’s single-engine Piper Malibu crashed about a mile from the Greensburg Municipal Airport, about 40 miles southeast of Indianapolis.

Those runway lights were checked after the crash and were found to be working properly, the report said.

Killed in the crash were: Horan, 46; his wife, Barbara, 45; and their friends Stephen Butz, 45, and Denise Butz, 42, all of Greensburg. The two couples were returning from Destin, Fla.

The preliminary report found Horan had been cleared to approach the Greensburg airport about 13 minutes before the crash when witnesses estimate cloud ceilings were at 300 feet.

The plane plowed into a field and came to rest nearly 300 feet away in a wooded area.

A report with detailed crash findings will likely take between six and nine months to complete, and the final crash report is expected in 12 to 18 months, officials said.

Agency spokesman Keith Holloway said investigators will examine the plane’s wreckage, GPS navigation devices recovered from the craft, witness interviews and the weather conditions at the time of the crash.