WARNING: Distressing content

The cockpit voice recorder is one of the most important, but haunting, remains from a plane crash.

One of two parts that make up the aircraft's black box, the cockpit voice recorder captures conversations and alarms on doomed planes to help investigators determine what went wrong.

But while those recordings are essential, they are often hard to listen to.

Here are some of the most chilling last words from the cockpit that capture panic, confusion and sometimes acceptance from the flight crew in the final moments before some of history's most infamous crashes.

Pakistan flight 8303

The Covid-19 pandemic has brought air travel to a virtual halt but 2020 was not without deadly crashes — and one of the worst was the crash of Pakistan International Airlines flight 8303 in Karachi in May.

Ninety-seven people on board were killed but, incredibly, two people survived when the plane lost two engines and crashed into a residential area after multiple attempts to land at Jinnah International Airport.

A transmission of the pilot's final exchange with air traffic control indicated he knew the Airbus A320 was having engine trouble.

"We are returning back, sir, we have lost two engines," the pilot said, according to an English transcript.

"Sir, mayday, mayday, mayday Pakistan 8303." Then transmission ended.

Survivor Mohammad Zubair told reporters the last thing he heard before the crash was the pilot telling passengers over the intercom they were experiencing engine trouble and the landing would be "troublesome".

Air France flight 447

All 228 passengers and crew died when Air France flight 447 from Rio de Janeiro to Paris plunged belly-first into the Atlantic Ocean in June, 2009.

For years, the cause of the crash – the worst in Air France's history – remained a mystery. Cockpit recordings would later reveal chaos in the cockpit as technical problems with the A330 were compounded by the fact the experienced pilot was asleep, leaving a rookie in charge as problems emerged with the tools that measure the plane's airspeed and altitude.

By the time the captain returned to the cockpit, the plane was stalling and it was too late.

"F***, we're going to crash! It's not true! But what's happening?" first officer David Robert yelled out as rookie co-pilot Pierre-Cedric Bonin struggled to control the plane.

As a series of alarms continued to sound, someone said: "F***, we're dead."

Captain Marc Dubois spoke last. "Ten degrees pitch," he said. Two seconds later, the plane crashed into the Atlantic Ocean, off the coast of Brazil, at 200km/h.

Lion Air flight 610

One of the worst recent aviation tragedies was the mysterious crash of a Lion Air flight into the Java Sea off Indonesia in October 2018.

All 189 people on board died when the plane crashed after a short and erratic flight. The incident was the first of two fatal accidents involving the new Boeing MAX 8 aircraft.

Six months after the crash, sources close to the investigation revealed contents of the cockpit voice recordings, which captured the pilots trying to understand why the plane was flying erratically.

The sources said the captain, who was flying the plane, asked the first officer to check the plane's handbook for checklists for abnormal events.

For the next nine minutes, the pilots remained calm as they tried to control the plane.

In the last seconds before the crash, the Indian-born captain was silent, and the first officer, from Indonesia, said "Allahu Akbar", or "God is the greatest".

Pacific Southwest flight 182

In September 1978, Pacific Southwest Airlines (PSA) flight 182 collided with a Cessna light aircraft as it was descending and about to land at Lindbergh Field, which is now San Diego International Airport.

There were 135 people killed on the Pacific Southwest plane, two on the Cessna and seven on the ground.

Due to the recording and subsequent inquiry, it was found the accident happened when the PSA crew lost sight of the Cessna and did not make that fact known to the air traffic control.

The recording from the PSA plane captures the sound of impact and the response of the flight crew in the following 20 seconds until the crash.

Captain: "What have we got here?"

First officer: "We're hit man, we are hit."

Captain (on radio): "Tower, we're going down, this is PSA."

Seconds later, the captain is heard again. "This is it, baby!"

The last words before the end of the recording are: "Brace yourself. Ma, I love you."

Tenerife airport disaster

It happened more than four decades ago, but the Tenerife airport disaster in Spain is still the deadliest plane crash of all time.

On March 27, 1977, two Boeing 747s — one operated by Dutch carrier KLM, the other by now-defunct Pan American — collided on the runway, causing a catastrophic fire that killed 583 people on both aircraft.

The crash happened after a series of unfortunate events resulted in the Pan Am plane being in the way of the KLM plane as KLM prepared to take off. The Pan Am crew could be heard shouting at the oblivious KLM plane thundering down the runway towards it.

"There he is!" Pan Am captain Victor Grubbs yelled, in a cockpit voice recording. "Look at him! Goddamn, that son of a b**** is coming!"

With that, the two mighty jets collided in a catastrophic crash that resulted in the highest aviation death toll on record.

United Airlines flight 93

United Airlines flight 93 was one of four commercial planes hijacked by al-Qaeda terrorists on September 11, 2001. The flight had taken off from Newark Liberty International Airport in New Jersey, bound for San Francisco with 44 people on board, including four hijackers.

Flight 93 crashed in an empty field in Pennsylvania. It was the only one of the planes hijacked on 9/11 not to reach its intended target. The 9/11 Commission concluded the hijackers crashed the plane to stop passengers and crew taking back control.

The cockpit recording captured demands from the terrorists who stormed the cockpit and pleas for mercy from the flight crew. The very final words were in Arabic: "Give it to me" was said eight times before the phrase "Allah is the greatest" was repeated over and over before the crash.

The last words from a member of the crew were: "Down. Push, push, push, push, push."

LOT Polish Airlines flight 5055

LOT Polish Airlines flight 5055 with 183 passengers and crew on board had taken off from Warsaw's Frederic Chopin Airport bound for San Francisco with a stopover in New York.

But it never left Poland.

Shortly after take-off, the May 9, 1987 flight ran into multiple catastrophic events affecting two engines and the plane's elevator. About 30 minutes after the first engine exploded, the plane landed in the Kabaty Woods on the outskirts of Warsaw.

The cockpit recording captures an "orderly response" from the flight crew as they discuss their options with air traffic control, according to Flight Safety Australia. The decision was made to try landing at Warsaw, but the plane didn't make it.

Those horrifying final words were said in Polish, but translated into English they were: "Goodnight, goodbye, we perish!"