DUBLIN (Reuters) - Delivery delays from planemakers Airbus and Boeing ( BA ) are "massively frustrating" and are not yet getting better, the head of the global airline body IATA said on Wednesday.

A number of Europe's leading airlines bemoaned the resulting capacity constraints at a conference in Brussels, with Ryanair saying it would have to revise down its passenger traffic estimates for next year because of the delays.

"It's massively frustrating for airline CEOs and it's having a big impact," International Air Transport Association Director General Willie Walsh told an Irish think-tank.

"It's going to be a problem I think for a number of years to come. The message I get from airline CEOs is the situation doesn't look like it's getting any worse, so it seems to have bottomed out or plateaued, but it's not yet getting better."

Boeing ( BA ) and Airbus have been struggling to meet delivery goals amid supply chain challenges. An ongoing strike at Boeing ( BA ) has raised concerns about worsening delays at the U.S. planemaker amid a broader crisis around its safety reputation.

The European airlines urged Brussels to do more to secure a level playing field in the industry, complaining that Chinese rivals enjoy a huge cost advantage because they can fly over Russia.

A number of carriers, including IAG-owned British Airways and Lufthansa, recently cancelled their routes to Beijing as they struggle with competition from Chinese airlines on Europe-Asia routes.

Walsh, a former head of IAG, said that to the best of his knowledge, the European Union did not have any way to retaliate against Chinese carriers, for example, who are flying through Russian airspace.

"Our view, from IATA point of view, is Russian airspace should be open to everybody. This is a political issue. It's not a security or safety issue," he told Dublin's Institute of International and European Affairs.

"I can understand why the airlines are calling for it, but I can't see any particular instrument available to address that."