• Boeing shares dropped Monday after South Korea ordered an inspection of all 737-800 planes — the model involved in a deadly Jeju Air crash over the weekend — operated by its domestic carriers.
• Uncertainty surrounds the exact circumstances of the crash, which killed 179 of 181 people on board the flight on Sunday.
• Acting President Choi Sang-mok told the Transport Ministry to carry out an emergency safety inspection of the country's entire airline operation system, while officials at the Ministry of Land, Infrastructure, and Transport, or MOLIT, said they would conduct a "comprehensive special inspection of the B737-800."

Boeing shares fell more than 2% on Monday, after South Korea ordered an inspection of all 737-800 planes — the model involved in a deadly Jeju Air crash over the weekend — operated by its domestic carriers.

Acting President Choi Sang-mok told the Transport Ministry to carry out an emergency safety inspection of the country's entire airline operation system, while officials at the Ministry of Land, Infrastructure, and Transport, or MOLIT, said they would conduct a "comprehensive special inspection of the B737-800."

Uncertainty surrounds the exact circumstances of the crash, which killed 179 of 181 people who were on board the flight on Sunday. The plane landed without the correct gear deployed at South Korea's Muan International Airport, skidded off the runway and smashed into a wall, bursting into flames. The survivors were two crew members who were pulled from the wreckage.

In a Monday briefing, MOLIT said the aircraft's pilot had mentioned a "bird strike" a few minutes after the airport's control tower issued a bird activity warning. The pilot also notified the control tower of a "go-around," referring to an aborted landing attempt, and declared "Mayday," said Yu Kyung-soo, director of aviation safety policy at MOLIT, according to an NBC News translation.

Two black boxes were retrieved from the aircraft and have been sent for analysis. The U.S. National Transportation Safety Board is meanwhile leading a team of U.S. investigators, including the Federal Aviation Administration and Boeing, to assist South Korea's Aviation and Railway Accident Investigation Board with a probe into the crash. Engine manufacturer CFM International, a joint venture between GE Aerospace and France's Safran Aircraft Engines, will also be involved in the investigation.

MOLIT officials said Monday they were reviewing the concrete wall that the aircraft hit for its connection to the accident in addition to the inspection of the 737-800s in South Korean airlines' fleet.

The popular Boeing narrow-body aircraft has been in operation for nearly three decades, with development predating the U.S. manufacturer's troubled 737 Max jets, a later iteration of the model. Aviation experts said it was unlikely that a design flaw played into Sunday's crash.

The Boeing 737-800 has a strong safety record and is one of the most widely used aircraft with about 4,400 in service, equal to about 17% of the active global jet fleet, according to aviation-data firm Cirium.

It is also commonly used by South Korean low-cost carriers, MOLIT said, with Jeju Air the biggest operator with 39 jets. Other operators include T'way Air, Jin Air, Eastar Jet and Air Incheon, while flag carrier Korean Air has two of the model.

"We will examine compliance with various regulations, including operational records, inspections, and maintenance conducted before and after flights," Ju Jong-wan, director of the Aviation Policy Office at MOLIT, said Monday, according to the NBC News translation.

"We plan to review strengthening regulations regarding bird strikes, identified as a potential cause of the accident, especially for new airports under construction."

A Boeing spokesperson told CNBC: "We are in contact with Jeju Air regarding flight 2216 and stand ready to support them. We extend our deepest condolences to the families who lost loved ones, and our thoughts remain with the passengers and crew."

Local media reported that another Jeju Air aircraft of the same model returned to South Korea's Gimpo Airport shortly after takeoff on Monday after reporting issues with its landing gear.

"The model and type of aircraft has a very strong safety record and over 200 airlines around the world have chosen to fly the Boeing 737-800 in the last year," Paul Charles, CEO and travel analyst at The PC Agency, said by email.

"The investigators will need to comb through every maintenance record relating to the 737-800s at Jeju Air to see if they offer up any further clues as to why the aircraft's landing gear did not come down."

At a press briefing Sunday, head of the management support office at Jeju Air, Song Kyung-hoon, said the airline would support the victims and their families, and that the aircraft was covered by a $1 billion insurance, according to news site Yonhap.

Song also denied that mechanical faults or inadequate safety preparations played a role in the crash.

"This crash is not about any maintenance issues. There can be absolutely no compromise when it comes to maintaining aircraft," Song said.

Shares of Jeju Air hit an all-time low Monday, according to FactSet, and closed down 8.65%.

— CNBC's Yeo Boon Ping and Leslie Josephs contributed to this story.