Updated

Work begins Friday to recover the remains of the four people who died when a small plane crashed into a flight training facility at a Kansas airport, authorities said.

Jet fuel from the plane burned so hot during the blaze after the crash Thursday morning at Wichita Mid-Continent Airport that portions of the building remained unsafe all day and emergency officials voiced concerns about the stability of the structure. Late Thursday night, smoke continued to rise from the wreckage.

Heavy equipment will be brought in Friday to remove portions of the building so firefighters can reach the victims, Wichita Fire Chief Ronald Blackwell said. Crews are expected to be at the site for at least a couple of days.

"The real work begins at daylight," Blackwell said Thursday.

National Transportation Safety Board investigator Leah Yeager said the pilot reported a problem with the left engine of the twin-engine Beechcraft King Air soon after taking off from the airport.

According to witness reports, the plane was "flying low and slow before it entered a left turn," Yeager said.

"It continued to turn left and then impacted the building," she said.

The plane, which was manufactured in 2000, struck the top of the building and ignited a horrific fire, Blackwell said. The aircraft remains in pieces, with parts scattered on the roof and on the ground of the training facility.

NTSB investigators at the scene will try to determine what caused the engine failure. Peter Knudson, an NTSB spokesman, told The Associated Press early Friday that there are procedures for pilots to land with an engine out but that he had no information on why those procedures were not applied.

Officials said only one person was onboard the plane and that everyone else inside the building had been accounted for. Doug Nolte, city police spokesman, said in a news release that three of the victims were from the Wichita area and one was from another country. Their names and ages have not been released pending notification of family members.

Five people were hurt in the crash. One patient was in serious condition at Via Christi Hospital St. Francis and four others have been treated and released, hospital spokesman Roz Hutchinson said.

Wichita Police Deputy Chief John Speer said the crash was an accident and "not an intentional act."

The crash did not significantly disrupt passenger traffic at the airport.

The aircraft was headed to Mena, Arkansas, for painting and interior refurbishing work with Rose Aircraft Services Inc., according to that company's CEO, Keith Rose, who offered his condolences to the victims' families.

Rose provided no further details on the plane or its pilot.

A tail number shows the plane is registered to Beechcraft Corp. Beechcraft spokeswoman Nicole Alexander confirmed in an email that the aircraft was registered to the company but said it was recently sold. She said she couldn't comment further and referred additional questions to the NTSB.

Located several miles west of downtown, Wichita Mid-Continent is used by private aircraft and served by several national airlines and their regional affiliates. It saw more than 13,000 departures and about 1.4 million passengers last year, according to the U.S. Department of Transportation.

The crash is the latest in a string of incidents at the airport. In December, an avionics technician was arrested and accused of trying to drive a van filled with inert explosives onto the tarmac. In January, an Oklahoma man rammed his pickup truck through a security gate at the airport.

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Reporters Heather Hollingsworth, Margaret Stafford and Greg Moore in Kansas City, Missouri, contributed to this story.