Aer Lingus has said it will be reviewing processes and procedures after images of a crowded flight with no social distancing appeared on social media.
The images, taken by a passenger on the 8.45am flight yesterday between Belfast City Airport and London Heathrow, caused public outcry on social media.
Passenger Sean Mallon, who was flying to Heathrow for work, told the BBC around 95pc of the seats on the flight were filled.
"There was no social distancing whatsoever," he said.
"Once we got to the other side I just wanted to get off the plane. Everyone just jumped up and started opening overhead compartments as normal, grabbing their bags, queuing to get off as normal. No change whatsoever."
Professor of molecular virology at Queen's University, Belfast, Dr Ultan Power said the images were "a major concern" but there was a more worrying issue.
"I would be even more concerned for the plane coming back in the opposite direction from a Covid-19 hotspot with potentially a lot of people who had been exposed to the virus," he said.
"By not ensuring quarantine we're almost guaranteeing we will have a reintroduction after the huge efforts of lockdown."
In a statement, Aer Lingus said it would be assessing the impact of traveller numbers on the Belfast to Heathrow service.
"In light of the unexpectedly high loads on the Belfast-London Heathrow service this morning and the level of demand for the route, Aer Lingus is reviewing its processes and procedures applicable to the operation of this service," the airline said.
"The safety and security of Aer Lingus' customers and crew is our top priority and any process changes that are identified as being required will be implemented as a matter of urgency".
Aviation analyst Alex Macheras said aircraft should not be an exception to social distancing rules.
"This is a disappointing revelation from Aer Lingus, who have decided to not social distance on board, which many other airlines have decided to do," he said.
"We are still in the middle of this pandemic and there is a lack of any clear direction for rules from regulators."