ATLANTA (AP) – A medical helicopter was not certified for flying in foggy, low visibility conditions when it crashed last month in Coffee County, killing all aboard including the patient, federal investigators say in a newly released report.

The National Transportation Safety Board released its preliminary report Monday on the crash, which took place shortly after midnight on March 26. Haynes Life Flight employees Stasi Cernadas and Jason Snipes; pilot Chad Hammond; and patient Zach Strickland died in the crash.

The NTSB report says fog and mist enveloped the landing zone in a farm field near the scene of the highway wreck when the helicopter arrived near midnight.

The poor weather continued 23 minutes later, when the helicopter took off with a patient. The helicopter managed to rise to 1,100 feet before crashing in a swampy area of Coffee County after landing near the scene of a one-vehicle accident on County Road 615.

The chopper “was not certified for flight” in such conditions, which require the use of instruments to maneuver through poor visibility, the NTSB report states.

Helicopters must have the equipment necessary to fly with instruments when visibility is poor, said Gary C. Robb, a Kansas City-based aviation lawyer who wrote the book “Helicopter Crash Litigation.” The NTSB doesn’t specify exactly why it found the Alabama helicopter wasn’t certified for flying in the poor weather.

NTSB spokesman Keith Holloway said “we’ve just documented what we know to be factual,” in the preliminary report.

“We haven’t determined whether it should have been flying that night,” Holloway added. “Part of our investigation is to look at everything, and whether or not the aircraft was certified to fly is part of that.”

It could take a year or longer for a final report that identifies a likely cause of the accident, federal authorities say.

However, the preliminary report on this crash is thorough, giving more detail than many others at this stage of an investigation, Robb said.

“In terms of what pieces of the puzzle do we have, right now it’s a 500-piece puzzle and this preliminary report gives us 200 pieces of that puzzle …,” he said after reviewing it.

The report details the condition of the aircraft and its parts at the wreckage scene, and notes that many components were working at the time of the crash.

“They were able to confirm that there was no breach of the ability to control the main rotor or the tail rotor or the engine,” Robb said. “The control system was intact. That’s critical.”

He said there were clear signs the engine was operating and producing power at the time of the crash, making it unlikely that any in-flight mechanical malfunction was to blame.

Shortly after the crash, NTSB spokesman Peter Knudson said the weather conditions and visibility would be a focus of the investigation.

Fog can lead to a phenomenon known as spatial disorientation. “It is defined as the pilot’s losing his or her orientation to the ground, plain and simple,” Robb said. “You don’t know where you are in space.”

The helicopter had been sent to the wreck by Haynes Life Flight dispatchers from its base at Troy Regional Medical Center in Troy, the NTSB said.

Kirk Barrett, chief operations officer of Haynes, an Alabama ambulance service, said in an email to The Associated Press Monday that questions should be directed to Louisiana-based Metro Aviation Inc., which operated the helicopter.

“Our deepest condolences are with all the families involved. At this time, the NTSB investigation is still ongoing and until that is complete, we are prevented from making additional comments,” Kristen King Holmes, Metro Aviation’s marketing director, said in a statement Monday.

The crash comes as the Federal Aviation Administration continues its efforts to improve the safety of the aircraft known as air ambulances. It began that effort after a series of deadly crashes.

The year 2008, for instance, “proved to be the deadliest year on record with five accidents that claimed 21 lives,” the FAA wrote in a fact sheet about the initiatives to improve safety.

On Feb. 20, 2014, the FAA issued new rules requiring air ambulances to have stricter flight rules and procedures, more training, and additional on-board safety equipment, according to the FAA document.