Questions grew on Tuesday over the crash of a Jeju Air jetliner as police rushed to identify victims and as families of those killed in the deadliest plane crash on South Korean soil pressed authorities for more information.

The National Police Agency said it is making all-out efforts by adding personnel and rapid DNA analysers to hasten the identification of the five bodies still unidentified as of Tuesday.

Family members gathered at the country’s Muan International Airport, where the crash occurred, have pushed for faster identification and more information from authorities.

All 175 passengers and four of the six crew were killed when a Jeju Air (089590.KS), opens new tab Boeing (BA.N), opens new tab 737-800 belly-landed and skidded off the end of the runway, erupting in a fireball as it slammed into a wall. Two crew members were pulled out alive.

South Korea’s acting President Choi Sang-mok on Monday ordered an emergency safety inspection of the country’s entire airline operation as investigators sought to find out what caused the deadliest air disaster on South Korean soil.

The Transportation Ministry said a “Black Box” flight recorder recovered from the crash site was missing key pieces and authorities were reviewing how to extract its data.

Inspections of all 101 B737-800s operated by South Korean airlines was scheduled to be completed by Jan. 3, while the airport would now remain closed until Jan. 7, the Transport Ministry added.

Representatives from the U.S. National Transportation Safety Board (NTSB), Federal Aviation Administration, and aircraft manufacturer Boeing have joined the investigative body and plan to meet in Muan on Tuesday.

The NTSB said in a statement it sent three investigators including people with specialties in operational factors and airworthiness to South Korea to assist the investigation.

“If we need more specialists we will send them,” board chair Jennifer Homendy said in an interview.

QUESTIONS ABOUT EMBANKMENT

Investigators are examining bird strikes, whether any of the aircraft’s control systems were disabled, and the apparent rush by the pilots to attempt a landing soon after declaring an emergency as possible factors in the crash, fire and transportation officials have said.

Officials have also faced pointed questions about design features at the airport, particularly a large dirt-and-concrete embankment near the end of the runway used to support navigation equipment.

The plane slammed into the embankment at high speed and erupted into a fireball. Bodies and body parts were thrown into surrounding fields and most of the aircraft disintegrated in flames.

South Korean officials say the embankment was built according to standards, and that there are similar features at other airports including in the United States and Europe.

But many experts said its proximity to the end of the runway defied best practices and likely made the crash far more deadly than it may have been otherwise.

The runway design “absolutely (did) not” meet industry best practices, which preclude any hard structure like a berm within at least 300 metres (330 yards) of the runway’s end, said John Cox, CEO of Safety Operating Systems and former 737 pilot.

The airport’s concrete berm appears to be less than half that distance from the end of the pavement, according to Reuters’ analysis of satellite images.

South Korean officials have said it is about 250 metres (273 yards) from the end of the runway itself, though a paved apron extends past that.

The plane appeared in video footage to be slowing down and in control when it went off the runway, Cox said. “When it hits that berm is when it turns into tragedy.”