A watchdog has found there was maladministration by a Stormont department over late-night flights at George Best Belfast City Airport.
Flights operating between 21:31 and 23.59 GMT are only permitted in "exceptional circumstances".
But the ombudsman found 3,073 such flights between 2008 and early 2016.
The Northern Ireland Public Services Ombudsman said there had been "a series of failures" by the former Department of the Environment (DoE).
For several years, the DoE did not gather data on late-night flight movements "on a regular and systematic basis", it said.
The investigation was carried out after a complaint was made by Belfast City Airport Watch, which represents residents.
Under its planning agreement, the airport is allowed to facilitate delayed flights - but only in "exceptional" situations.
However, the ombudsman said the department should have had an "agreed understanding" of what this meant in practice, so people living close to the airport knew "what was intended by this obligation".
It has recommended an operational definition should now be reached between the Department for Infrastructure, which has replaced the DoE, and the airport.
A complaint was made to the ombudsman on behalf of Belfast City Airport Watch, which claimed the airport was "abusing the exceptional circumstances clause".
Spokesperson Mari Fitzduff said: "We have spent years trying to convince the authorities they needed to take action on this issue.
"What is important now is that the department acts on the report's recommendations as quickly as possible."
A spokesman for the airport said it was "fully compliant" with its operating agreement, adding: "No airport in the world operates without delays."
The 3,073 flights "accounted for only 1.04% of all total aircraft movements" during the period in question, added the spokesman.