The Transportation Safety Board says two pilots involved in a fatal mid-air collision over a busy suburban Montreal shopping mall in March 2017 weren’t adhering to altitude restrictions.
In a report released Wednesday, Canada’s transport safety watchdog says neither pilot respected restrictions set out by air traffic control at nearby Saint-Hubert Airport.
Both pilots were flying solo.
READ MORE: ‘Are you listening?’: Air traffic controller tries to warn pilot moments before crash in Saint-Bruno
A Cessna 152 operated by a pilot undergoing commercial training with Cargair was returning to the airport from a training session and collided with another Cessna 152 that had taken off from the airport.
WATCH BELOW: 1 dead, 1 injured in plane collision
The planes collided 457 metres above Promenades Saint-Bruno, with one pilot killed and the other one seriously injured.
One plane landed in the parking lot while the other crashed on the roof of the shopping centre.
The Cargair plane descended 30 metres below its restricted altitude level of 488 metres while trying to fix a telecommunication issue, while the other plane climbed 121 metres above its restricted level of 335 metres, colliding with the Cargair plane from below.
Neither pilot saw the other aircraft.
The board said both pilots were international students enrolled in flight training.
While neither pilot had English or French as their mother tongue, investigators say both had proficient English assessed as “operational,” meaning they met a minimum international proficiency level to be able to communicate with air traffic control.
READ MORE: 1 dead, 1 injured after planes collide over Montreal south shore shopping mall
The TSB says its investigation also found that air traffic control is complicated at the St-Hubert by four flying schools and a varying level of flying skills and language proficiency among the student pilots.
And the probe showed that Transport Canada’s verifications of aviation language proficiency training is strictly administrative.
Following the crash, the federal agency published a safety alert recommending schools ensure student pilots have their language proficiency tested before their first solo flight.
WATCH BELOW: Two planes collide over Promenades Saint-Bruno mall