The Irish Aviation Authority has issued new operating instructions to pilots working out of Dublin Airport on discovering that a massive crane had been erected close to flight paths.
An IAA spokeswoman said the presence of such a large, unlit structure in the vicinity of the airport represented a potential safety risk to aircraft.
The authority is now considering a prosecution over the failure of a building contractor and Dublin City Council to notify it of the erection of the 83-metre crane at Santry Cross in Ballymun.
Concern has also been expressed within the authority about the erection of a 52-metre building - almost the same height as Liberty Hall - on the site, so close to the airport.
Neither the IAA nor Aer Rianta was formally notified of the plan to build the 16-storey apartment block at Santry Cross, the authority has pointed out in a letter to the council.
Both bodies are statutory notice parties under the planning laws, which state that the assessment of proposals for high buildings must take into account their effect on air navigation. Any structure or mobile object 45 metres or more in height is defined as an obstacle.
"This structure will penetrate defined protected structures for Dublin Airport, thereby imposing operating restrictions on the airport. This authority needs to be notified of the erection of any such obstacle and is considering initiating a prosecution in this case," according to IAA aeronautical officer Mr Pieter van Velzen, in a letter to the council last February.
After discovering the existence of the crane, the authority directed that it be lit with aviation warning lights and horizontal bands of high-visibility red and white paint.
This has been complied with.
Pierse Contracting, which obtained planning permission in May 2003, is building 340 tax-incentive apartments in two blocks on the site, as well as 20 shops and restaurants. The €100 million scheme, which is largely sold out, is a centrepiece of the Ballymun regeneration project. Attempts to contact Pierse Contracting for comment were unsuccessful.
According to the IAA spokeswoman, pilots flying into certain runways at the airport have been told to approach at a greater height as part the new operating guidelines. She declined to comment further, saying the matter was under investigation.
Mr van Velzen has sought an assurance from the council that the authority will be notified of all future planning applications for high buildings. A statement to this effect should be included in the Dublin City Development Plan, currently under preparation, he has recommended.
