Under its planning agreement, the airport is allowed to facilitate delayed flights – but only in “exceptional” situations.
The investigation was carried out after a complaint was made by Belfast City Airport Watch, which represents residents. The complaint claimed the airport was “abusing the exceptional circumstances clause”.
The Ombudsman said there had been “a series of failures” by the former Department of the Environment (DoE).
He 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”.
He has recommended an operational definition should now be reached between the Department for Infrastructure, which has replaced the DoE, and the airport.
Belfast City Airport Watch 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.”
