A potentially terrifying situation unfolded on a flight out of Toronto Pearson Airport earlier this month, after a flight crew member became "incapacitated." 

The incident occurred on an Air Transat aircraft performing flight TS-186 from Toronto to Punta Cana International Airport with 299 passengers on board. 

The flight took off from Toronto just after 9:30 a.m. on Monday, Nov. 20, and was due to arrive in the Dominican Republic at approximately 2 p.m. local time. 

While en route to the destination, one of the aircraft's flight crew members reportedly became incapacitated, although it was not specified by the Transportation Safety Board of Canada (TSB) what their role was on the aircraft. 

The incident occurred approximately three hours into the flight, and luckily, the crisis was quickly averted after a company-qualified pilot who was flying as a passenger stepped in and replaced the incapacitated flight crew member.

Shortly after, the crew performed a descent and continued on to the destination for a safe landing about one hour later without any other reported injuries. 

According to the electronic aviation repository, SKYbrary, crew incapacitation involves a situation where one or more crew members are no longer able to perform their job to the required level, and may range in severity from something as simple as dizziness to more extreme cases like unconsciousness. 

Regardless of severity, crew incapacitation is always treated as a serious matter as it can potentially "hamper the ability to control the aircraft," resulting in a major safety hazard.