An air-safety expert says that despite Iran's denials, investigators will be able to tell if a missile caused Ukraine International Airlines Flight 752 to crash

• Iran has thoroughly denied that the plane crash that killed 176 people on Wednesday was caused by one of its anti-aircraft missiles.
• However, the US, UK, and Canadian governments have said that a large body of intelligence suggests that Ukraine International Airlines Flight 752 was shot down, likely by mistake.
• Business Insider spoke with an air safety and crash investigations expert who explained that, given access to the plane's black box and debris, investigators should be able to prove definitively whether a missile hit the plane.
• Sign up for Business Insider's transportation newsletter, Shifting Gears, to get more stories like this in your inbox.
• Visit Business Insider's homepage for more stories.

Iran has denied allegations that it mistakenly shot down a Ukrainian plane outside Tehran on Wednesday, calling them a "big lie" and offering what it describes as "proof," while accusing the US, along with Canada and the UK, of carrying out a "psychological operation" to try and discredit it.

However, an air safety and accident investigations expert explained to Business Insider that when a missile strikes a plane, there are telltale signs investigators can use to make that determination.

US, Canada, and the UK have said their intelligence indicates that the plane, Ukraine International Airlines Flight 752, was shot down by an Iranian surface-to-air missile.

Initially after the Boeing 737-800 crashed early Wednesday morning, killing all 176 on board, Iranian officials said that the plane experienced a mechanical problem. Officials later appeared to walk back the statement, but have denied that a missile caused the crash.

Dr. Daniel Kwasi Adjekum, an assistant professor of aviation at the University of North Dakota with more than 20 years of aviation safety expertise, said that an examination of the plane's black box - the flight data recorder and the cockpit voice recorder - along with the wreckage of the ground, should be able to definitively prove if a missile hit the plane.

"The sound of an aircraft decompression" - which would be cause if a missile or shrapnel from it hit ruptured the plane's fuselage - "is unique and will be recorded in the cockpit voice recorder, while the sudden loss of cabin pressure, electrical systems and other vital flight parameters including changes in altitude, speed and directions after impact will all be captured in the cockpit voice recorder," he said.

While data from the black box can rule out a number of possible causes, and provide evidence that suggests that the plane was shot down, an examination of debris and remnants from the plane will also be necessary.

"Missile projectile shrapnel creates unique ' capture marks' on the wreckage, and pieces will be embedded in the wreckage," he said. "If that's the case, forensic trace analysis conducted as part of metallurgical test on wreckage will show chemical and other physical residues of the projectile."

Iran has previously suggested that it would not send the black box to Boeing for data recovery, which would typically be the norm. However, it has invited foreign investigators - including from Ukraine, Canada, and the US - to participate in the crash investigation.

"It's good for all parties to have everyone involved," Adjekum said. "It adds integrity to the investigation and the findings."

One consideration is that advanced data retrieval technology could be required to assess the black box if it was damaged in the crash. While Iran has said it would analyze the recorders in its own laboratories, Adjekum said he doubts the Iranians' capabilities.

"I personally think it would be better if it was done here in the US, or in France, since it's a neutral country in all of this, and has a capable lab," he said. "That would avoid the suspicion and politics."

While Iran has said that the plane appeared to turn around while on fire, attempting to return to the airport before crashing, Adjekum said that would not necessarily preclude a missile or projectile strike.

"When an aircraft is hit by such projectiles but not at a large surface area, there might not be immediate break up of the aircraft," he said. "It is possible the pilots had some level of control after such a hit and attempted to turn back to the airport."

"However, it would not be easy dealing with the cascades of failing systems after such hit, and at such relatively low altitudes, time for recovery and useful action by crew would be limited," he added. "Also, due to possibly effects of explosive decompression, it could be difficult to control the aircraft."

Ultimately, Adjekum said, it would likely be possible to prove the missile strike based on the variety of factors, combined with the radar signature captures and other intelligence that authorities have cited.