By Jack Kim SEOUL (Reuters) -Both engines of the Jeju Air plane that crashed last month contained duck remains, according to a preliminary report on Monday, with authorities still trying to determine what caused the deadliest air disaster on South Korean soil.

South Korean authorities concluded search and recovery operations and an investigation into the Dec. 29 crash of a Jeju Air plane that killed 179 people. The Korea JoongAng Daily said Sunday that the families of the victims agreed to end the investigation after authorities disclosed details about bird strikes linked to the crash.

Pilots’ actions after that strike are an early focus of the investigation, according to people familiar with the probe.

South Korea's authorities investigating last month's Jeju Air plane crash have submitted a preliminary accident report to the U.N. aviation agency and to the authorities of the United States, France and Thailand,

The nation’s transport ministry reviewed structures near airport runways after the deadly crash of a Jeju Air flight late last month.

The ill-fated Jeju Airplane in last month's deadly crash received a warning from air traffic control about bird activity just one minute before its black box recording stopped, the transport ministry said Saturday.

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South Korean authorities have submitted their preliminary findings on the Jeju Air crash that killed 179 people to the International Civil Aviation Organization (ICAO) and aviation authorities in the United States,

The South Korean Ministry of Transport announced that it will release a preliminary report on the Jeju Air plane crash by Monday. The accident claimed the lives of 179 people, with two miraculously surviving.

South Korea will release by Monday a preliminary report on last month's Jeju Air plane crash that killed 179 people, the deadliest air disaster on the nation's soil, the transport ministry said on Saturday.