At least one senior Royal Canadian Air Force officer is under investigation by the military police unit that probes major crimes for alleged negligence relating to a deadly helicopter crash six years ago in Afghanistan.

CBC News has confirmed that the Canadian Forces National Investigation Service is looking into allegations of negligence related to an incident on July 6, 2009, when a CH-146 Griffon crashed with six people on board.

All survived the impact, but three soldiers — including two Canadians, Master Cpl. Patrice Audet, 38, and Cpl. Martin Joannette, 25, and British Capt. Ben Babington-Browne, 27 — died after being unable to escape the flaming wreckage.

"This investigation is ongoing and no further information can be provided at this time," a military police spokesperson said in an email.

Heavily redacted report

Initially the crash was blamed on "pilot technique" and sandy ground conditions.

Those conclusions were based on a heavily redacted board of inquiry report released two years after the crash.

CBC News has since obtained a less-redacted version, along with the flight safety investigation report.

According to both reports, there are at least two underlying issues — the flight crew had too little training and the helicopter carried too much weight.

The crash involved a CH-146 Griffon helicopter. (Canadian Forces)

On July 6, 2009, the Griffon took off from a sandy area. The down force of the spinning blades created a "dust ball," which reduced the pilot's visibility.

Dust ball training is mandatory for all flight crews, who usually did exercises before and during their deployment to Afghanistan.

However, "the vast majority of the [Canada Helicopter Force, Afghanistan] aircrew only received the theory portion of the dust ball training," the board of inquiry report said.

Some pilots only got to watch the manoeuvre, not attempt it.

In this specific case, prior to his deployment "the [pilot] only observed a demonstration of the landing technique rather than practised dust ball landings himself," the flight safety report said. "Additionally, the [pilot] did not observe or complete any dust ball takeoff techniques."

Put simply, the pilot blamed for crashing the helicopter was allegedly sent to Afghanistan lacking the training to take off and land in sand.

Griffon weight limits modified

The original weight limit for the Griffon helicopter in Afghanistan was between 10,300 and 10,700 pounds.

But senior officials thought the weight cap would limit operations.

The weight cap "would significantly impair the ability of the unit to fulfil the entire spectrum of operations in support of the Joint Task Force," the board of inquiry report heard from military commanders.

So they changed the flight manual.

"The modified operating limitations in Section 1 of the flight manual restricted the Griffon to between 11,750 and 11,900 lb.," the board of inquiry report said.

Weight limit 'unknowingly' tested

Helicopter payload calculations are complex.

If a helicopter is close to the ground, it needs less power. The air its rotor forces downward bounces off the ground and creates a type of cushion.

To rise above that cushion and maintain altitude, more power is needed. A helicopter loaded to its maximum weight might be able to take off, but would have difficulty climbing above a certain height.

These two height zones are called "in ground effect" or "out of ground effect."

"In Ground Effect" vs. "Out of Ground Effect" <a href="https://t.co/uavGXY8C9H">pic.twitter.com/uavGXY8C9H</a> —@Brett_CBC

That height as well as the weight and power calculations change with air temperature and altitude above sea level.

Investigators compared the Griffon's payload to all possible weight limits.

The board of inquiry report found it exceeded those limits "by between 1,020 lb. to 1,320 lb." The flight safety report found it may have been as much as 1,720 lb. overweight.

"The Griffon flight [crew] was unknowingly flight testing the performance information found in the flight manual," the board of inquiry report found.

"The crew attempted to conduct a takeoff not knowing that the aircraft had an insufficient margin to remain within engine limitations," the flight safety found.

New allegations prompt investigation

These report observations went largely unnoticed for years.

But recently, a former Royal Canadian Air Force flight instructor began raising concerns about the incident.

"As a former helicopter pilot, I was stunned by what I read," said retired captain Anthony Snieder.

Snieder said he began looking into the crash after noticing safety violations in Moose Jaw in 2012. He was stationed at 15 Wing Moose Jaw teaching air force pilots.

He looked back at previous incidents and found issues with the Griffon crash.

Retired Capt. Anthony Snieder (Facebook)

"We have limitations for how to operate the aircraft, and they were intentionally violating aircraft limitations," he said.

As a result of voicing his concerns, Snieder said, he was reassigned to an office position and publicly discredited. He filed a harassment claim with the military, but it was dismissed. At that time Snieder asked to be released from the military.

Snieder has since applied to Federal Court for a judicial review of the dismissal of his harassment claim.

Amid his court battle, Snieder contacted the military police.

"If you do any act that could likely cause the destruction of an aircraft, it's against the law and you go to jail for it," Snieder said.

The Canadian Forces National Investigation Service is a unit with the military police that independently investigates serious and sensitive matters. Their jurisdiction covers Department of National Defence (DND) property, DND employees and Canadian Forces personnel serving around the world.

An official tells CBC News that "in all cases, investigations are conducted to determine the facts, analyze the evidence, and if warranted, lay appropriate charges."