The company has been facing its worst ever crisis after an Ethiopian Airlines' 737 MAX plane crashed, killing all 157 people on board, in the second fatal accident involving the jet in just five months.
"We would like to sincerely apologise for the inconvenience caused", the airline said.
Speaking on CNBC on Wednesday, Delta Air Lines CEO Ed Bastian said he believed consumer confidence would take a while to restore, and that a MAX return to service was "probably going to be longer than anyone would like it to be".
Cork Airport managing director Niall MacCarthy said he regretted the grounding of Norwegian's aircraft.
Boeing Co.'s 737 Max aircraft, grounded since March after two fatal crashes in five months, should be back in the air by December, a top United States regulator said.
Neither Boeing nor the Federal Aviation Administration has given a clear, public indication of when the 737 Max will receive approval to resume making commercial flights in the USA.More news: Donald Trump Jr. arrives for Senate testimony on Capitol Hill
More news: Elon Musk talks up Tesla's 'Cyberpunk truck,' and 400-mile range EVs
More news: French Open 2019: Rafael Nadal Wins His 12th Title at Roland Garros
"Boeing is now providing additional information to address Federal Aviation Administration (FAA) requests that include detail on how pilots interact with the airplane controls and displays in different flight scenarios", the representative said.
Southwest, the largest global operator of the MAX with 34 jets, had previously said it was cancelling flights through August 5.
On the other hand the American airline American Arlines announced on Tuesday that it canceled as a precaution all its flights with the Boeing 737 MAX until September 3, making it clear that the ban would not be lifted soon. Together, both tragedies left 346 dead.
Public uncertainty around the 737 Max's return comes as Boeing faces mounting pressure from lawsuits and investigations related to the aircraft, as well as potential issues with the wings of both 737 Max and 737 Next Generation planes.
"We offer our apologies to our customers impacted by this change, and we thank them for their continued patience", the airline said in a statement.