A fiery plane crash on a busy street near Vancouver International Airport two years ago was caused by the pilot losing control of the aircraft during the landing, following a chain of events started by an unsecured oil cap on the left engine, investigators have concluded.

Bill Yearwood, who delivered the Transportation Safety Board's final report Wednesday at a press conference in Richmond, B.C., said the crash ultimately resulted from a combination of events and decisions, none of which alone was responsible for the crash.

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TSB spokesman Bill Yearwood says a combination of decisions created a chain of events that caused the fatal 2011 crash. (CBC)

"The accident was caused by a chain of events combined with a lack of information which led the pilot to momentarily lose control at a critical altitude," the TSB spokesman said. "He was recovering the aircraft, but ran out of time and altitude."

The Northern Thunderbird Beechcraft King Air crash-landed on a six-lane Richmond street during rush hour shortly after taking off on Oct. 27, 2011.

Five male and two female passengers escaped after bystanders entered the burning plane, but the two pilots were trapped inside the cockpit and later died from their injuries.

Problems began 15 minutes into flight

The TSB determined that the flight out of Richmond was uneventful for about 15 minutes, as the plane climbed to 4,900 metres. When the captain noticed an oil leak on the left engine he decided, as a precaution, to turn around and return to the airport.

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The plane turned around over Golden Ears Provincial Park and began returning to Richmond, B.C., after the pilot noticed the left engine's oil leak. (TSB)

The captain handed the controls to his co-pilot and informed the passengers that they would be returning to Vancouver airport because of an "oil issue." Yearwood said that the captain and co-pilot consulted an in-flight checklist, and decided that if the oil pressure dropped too low, they would shut down the engine.

As the plane returned to the airport, the pilot was asked by the control tower if he needed emergency equipment on the runway. He declined because an oil leak is not considered an emergency unless there is a loss of oil pressure, which there wasn’t, according to the TSB report.

Data recovered from the crashed plane showed that as the plane approached the airport, it was going below target speed for reaching the runway.

The pilot adjusted the power on only one engine as the plane approached the runway, the report says, and that's when the plane went out of his control.

"The aircraft yawed to the left, rolled about 80 degrees, [and] pitched down about 50 degrees. After the pilot reduced power he was able to regain wings level, and pulled the nose up from 50 degrees and was down to 30 degrees ... and that is the angle that the aircraft hit the ground on Russ Baker Way," Yearwood said.

Fire killed pilots, not the crash

When the pilot lost control, the plane was at about 100 metres in altitude and just short of the runway, the report says.

As the aircraft rolled left and pitched down, it collided with a lamp post, clipped a vehicle and crashed on the busy roadway and burst into flames.

People from offices in the area and passing cars rushed to the scene and pulled the passengers out of the burning aircraft.

Pilots Luc Fortin and Matt Robic were trapped in the cockpit until fire crews arrived. They were taken out of the plane alive, but died in hospital.

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The pilots died due to burn-related injuries. Other than the fire that broke out after touchdown, the crash was survivable, the TSB said. (Steve Smith/Canadian Press)

Yearwood said the TSB's investigation determined that the battery was live as the plane crashed, and arcing wires likely sparked the fire.

"This was a survivable accident outside of the fire. Both pilots died from burn-related injuries," Yearwood said. "Of course, we believe more needs to be done to reduce the risk of post-crash fires."

The TSB says it is concerned that if Transport Canada doesn't address recommendations made in a 2006 TSB safety study, ignition sources will continue to be major risks.

All of the passengers were hurt, some with serious spinal injuries and paralysis. Six of them eventually launched a civil suit against the airline, Northern Thunderbird Air.

Oil cap problem flagged in service bulletins

After the crash, some of the passengers told the media they noticed oil under the left wing of the aircraft when they boarded. One of the passengers even managed to snap a picture of the leaking oil.

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Leaking oil could be seen on the plane's left engine. (Transportation Safety Board)

The TSB also found that the leaking oil was caused by an unsecured oil cap on the left engine. The oil cap on the left engine was not tightly latched.

"We found the day after the accident that this was a key event," Yearwood said.

Although no oil pressure was lost, and although the leak itself didn't cause the crash, the leak did initiate the series of events that led to a catastrophic outcome, the TSB found.

The TSB says that the factors leading up to the crash go back to 1995, when the engine's manufacturer issued a bulletin about a fix to restrict oil loss resulting from the oil cap being left unsecured. Service personnel were not latching the cap properly, which was causing mid-flight oil leaks.

Yearwood said it's clear that that bulletin, which was not a mandatory Transport Canada release, didn't fix the problem, as a similar bulletin for that particular model of Pratt & Whitney engine was re-released in 2010.

Key findings note training needs

Yearwood stressed that the problems with the cap alone were not to blame for fatal outcome.

"This is clearly an example of a chain of events where if you broke any one of then, it likely might not have happened," Yearwood said.

The TSB found that modifications had been made to the plane and the number of propeller blades, which changed the amount of drag on propellers and the response of the engines.

In addition, Yearwood said that training and manuals don't contain cautions about minimum speeds in cases where engines are being used with different amounts of thrust.

"The board found that there is a risk: Pilots will not anticipate aircraft behaviour when using asymmetric thrust near or below unpublished critical speeds and will lose control of the aircraft. And that is precisely what happened in this occurrence."

"We know this is an accident, and the crew were making their calls based on their best knowledge."

Lawsuits pending

Northern Thunderbird Air refused an on-camera interview Wednesday and cited pending lawsuits as its reason for having little to say.

In a statement, the company said, "This accident marks a tragic day in our history and remains a sombre memory for all affected."

"Our thoughts are with the families of the flight crew members, and the surviving passengers."

"While the aviation industry continuously dedicates enormous resources and manpower to preventing all accidents, this report will hopefully serve to further promote aviation safety."

Transport Canada also declined an interview, saying it will provide an official response to the TSB within 90 days.

Spokeswoman Maryse Durette said in a written statement, "Transport Canada takes all transportation accidents seriously and thanks the board for their work in this investigation."

"To reduce the number of post-impact fires and increase survivability of passengers, Transport Canada and other regulators continue to work towards developing improved standards.

"In this particular case, part of the challenge is finding solutions that would apply to a wide range of aircraft.  

"Be assured that we continue to seek ways to reduce the number of fatal accidents involving small aircraft."

Kill switches proposed 

The TSB's conclusion that "this was a survivable accident outside of the fire" has raised the issue of so-called kill switches, which would give a plane's electrical supply automatic turn-off capabilities.

The board says the fire that consumed the King Air plane could have been avoided if the plane's battery had automatically disconnected upon crash impact.

However, the King Air was only equipped with a manual power switch.

Aircraft specialist Rick Church did the pre-purchase inspection of the King Air plane before it was sold to its last owner, and he says the power switch could have helped if used in time.

"With a single action it'll shut off the master switch, all the electrical to the entire aircraft from the battery side and also both generators at the same time," he said.

But by the time the King Air plane hit the ground, the pilots were in no condition to access the switch.

The TSB wants small planes equipped with kill switches, to take the pilots out of the equation, but so far no one has moved to implement the change.

Federal NDP transportation critic Olivia Chow said the idea has been around since 2006, but the TSB has no power to act.

"Right now, our watchdog is toothless. Their recommendations sit on the shelf while this government is idle and sits on its hands," she said. 

"I believe the Transportation Safety Board should be given the power to enact immediate regulations on an interim basis."

However, Church is not convinced by the idea of a kill switch.

"I don't have a direct suggestion to replace an automatic shut-off. But I am concerned about a system like that acting on its own when it isn't needed. That would be a real problem."

A total of 247 King Air 100s were built in the 1960s and '70s. Approximately a hundred of those are still flying.

With files from the CBC's Bob Keating