US airlines have been ordered to inspect or replace cockpit windows on more than 1,200 Boeing jets to prevent possible cracking or fire due to loose wires in an electrical anti-icing system.

The Federal Aviation Administration (FAA) directive covers 757, 767, and 777 aircraft flown by most major airlines. The agency plans to propose a similar order for 747 jumbo jets in coming months since its windows are similar.

The directive is aimed at preventing cracking, smoke or fire from wires embedded in glass layers of the front cockpit windows. Side windows are not included.

There have been 11 reports of fire or flames over the past 20 years on the three Boeing models due to suspected loose screws or screws that were improperly tightened or threaded, the FAA said.

The most recent incident led to an emergency landing in Washington of a United Airlines 757 in May.

There are 1,200 affected aircraft flown by US airlines and 2,600 operating worldwide. Foreign safety agencies usually follow FAA directives with their own orders.