MONTREAL, Oct 24 (Reuters) - A shortfall of air traffic

controllers in Canada is at times forcing airport towers at

Kelowna and Winnipeg airports to close when the one controller

on duty goes on a break, according to a memo to Air Canada ( ACDVF )

pilots seen by Reuters.

Air Canada ( ACDVF ) advised its pilots to avoid the two airports in

the provinces of British Columbia and Manitoba when staffing

shortages are severe enough to shut their air traffic control

towers, the October 14 memo said.

It was unclear how often the airports have been closed and

their representatives did not immediately respond to requests

for comment.

The memo said NAV CANADA, which manages the country's civil

air navigation system, has advised airlines that air traffic

control shortages will occur at Winnipeg and Kelowna, "but this

could expand to other airports."

NAV CANADA said in a statement on Thursday that closures in

Winnipeg and Kelowna are planned for "low traffic periods to

minimize impact" and are being taken to ensure safe operations

and employees' well-being. It did not provide details of normal

staffing levels at those towers.

The closures are the latest instance of a North American

shortfall of air traffic controllers leading to potential flight

delays and added costs for carriers. In Canada, affected flights

would need additional fuel, for example, as they might need to

stay in a holding pattern or divert due to a controller staffing

shortage closure, the memo said.

Air traffic control staffing is of particular concern in the

United States due to a government shutdown, with the Federal

Aviation Administration saying this week that the problem has

delayed travel at several airports.

Nick von Schoenberg, president of the union which represents

Canadian controllers, CATCA, said the Canadian airport closures

were broader than just Winnipeg and Kelowna and were intended to

provide fatigue-related breaks for controllers. They "indicate a

lack of resilience in the system due to staffing challenges," he

said.

Tim Perry, president of the Air Line Pilots Association in

Canada, which represents Air Canada ( ACDVF ) pilots, said the lack of

stability due to shortages must be addressed.

"Air traffic controller shortages continue leading to delays

at various airports across Canada," he said.