Air Canada has said that four passengers and crew from the fatal collision at LaGuardia on Sunday night are still being treated in hospitals almost four days after the accident.

An investigation by the National Transportation Safety Board is well underway after two pilots were killed when their Air Canada flight collided with a Port Authority fire truck shortly after the jet landed in New York.

Pilot Antoine Forest and co-pilot Mackenzie Gunther, both Canadians, died in the collision, and more than 40 passengers and crew were admitted to local hospitals, authorities said.

While most survivors were released soon after their hospital admission, some were seriously injured, and Air Canada said in a statement Wednesday: “As of today, four of the injured passengers and crew remain in hospital.”

The airline didn’t specify whether the patients were crew or passengers, nor did it provide information on the nature or extent of the injuries.

As for Flight 8646, operated by regional airline Jazz Aviation, the wreckage has been released to Air Canada’s maintenance teams in New York and is due to be towed to a hangar “as soon as it is safe,” the airline said.

Pictures from LaGuardia showed the plane — which is missing its entire cockpit after the ferocious collision — being wheeled backwards away from the crash site, under the careful watch of airline staff on the ground.

“Once the aircraft is in the hangar, Air Canada teams will begin the process of reuniting people with baggage and personal belongings. Items will be safely returned as soon as possible, although the process of sorting and identifying all belongings from the aircraft will take time,” the statement added.

Passengers on board the stricken flight paid tribute to the death pilots for their quick reactions and braking to minimize the impact.

“I think everybody on that plane feels very grateful that they’re all alive, and they all pretty much give it to the pilots,” Jack Cabot, 22, who was returning home from a spring break ski trip, told NBC News on Wednesday.

The investigation is likely to focus on the role of air traffic controllers, the chain of events leading up to the collision, and the apparent failure of multiple safeguards and systems designed to prevent such an accident.

NTSB chairwoman Jennifer Homendy told a news conference Tuesday that a safety system called ASDEX failed to generate an alert “due to the close proximity of vehicles merging and unmerging near the runway.”

Air Canada CEO Michael Rousseau came under fire from Canadian Prime Minister Mark Carney on Wednesday for not issuing a statement in French after the incident. In a four-minute video, Rousseau said two words in English — Canadian public officials typically give announcements in English and French.

“I’m very disappointed – as others are, rightly so – in this unilingual message of the CEO of Air Canada … [it shows] a lack of judgment, a lack of compassion,” Carney told reporters

The Canadian parliament’s language committee voted Tuesday to summon Rousseau to appear in Ottawa to answer questions.