The Civil Aeronautics Board late last week disapproved as "plainly anticompetitive" the method by which takeoffs and landings have been allocated to commuter airlines at National Airport for the last dozen years.

In a unanimous decision, the board said the existing agreement among commuter airlines allows the incumbents to hold on indefinitely to their slots--as takeoffs and landings are called--and contains no provision for accommodating new entrants or expanding operations.

Finding that the previously approved agreement among commuter airlines "clearly violates antitrust principles," the board gave the commuters six months to come up with a new method for allocating the limited landing and takeoff privileges at National.

The board also criticized the Federal Aviation Administration for limiting the operations of commuter airlines at National. Absent the FAA's restrictions, "all commuter operations could be accommodated without an adverse impact on noise or congestion on a first-come, first-served basis," the board said.

The commuter airlines have been meeting, with CAB approval, since 1969 to allocate slots among themselves at National, one of four "high density" airports whose access has been limited by the FAA. Similar slot-allocation meetings have been held by the scheduled airlines since 1968. However, the two government-sanctioned committees operate very differently, according to the CAB.

Under the operations of the commuter committee, the CAB said, no commuter airline can receive a slot unless, first, an incumbent relinquishes one and, second, no carrier higher on the seniority list claims it.

Since seniority is based on length of service as a scheduled commuter at National, new carriers, having no seniority, are placed at the bottom of the list as they request slots. Also, only carriers having slots already can vote or otherwise participate in the business of the committee. Prospective entrants, therefore, "have no power to alter the procedures which deny them access to National Airport," the CAB said.

In contrast, the scheduled airlines' committee is a "materially less anticompetitive" alternative, the CAB said. It does not authorize the "grandfathering" of slots; it permits the equal participation of all airlines authorized to use the airport, whether they have started service or not; it provides for the periodic reallocation of all the slots; and it requires unanimous approval for a slot allocation agreement to be reached.

Although it rejected the commuter agreement, the CAB deferred final action on the airlines' scheduling committees pending development by them of contingency plans to deal with scheduling deadlocks. As airline deregulation spawned new airlines and gave existing airlines easier access to new routes, the certificated airlines increasingly have found it difficult to reach scheduling agreements.

In its decision, the CAB also urged the Department of Transportation and the FAA to reexamine the "high-density rule" altogether to determine if the congestion problems are sufficiently serious at the four restricted airports "to warrant this limitation on competition . . .

"If the rule is not needed for safety reasons, and there are other constraints--such as noise or groundside congestion--which justify limiting access, then we urge DOT and the FAA to adopt a procompetitive system which directly addresses those constraints," the board said.

Currently, the four restricted airports are operating at reduced levels because of the strike-caused understaffing of the air traffic control system.

At National, airlines have been limited to 40 slots an hour, commuters to eight an hour and private aviation to 12 an hour.

Under a not-yet-implemented plan for National, the airlines' slots would be cut from 40 to 37 an hour and the three remaining would be given to the commuters. Many of the airlines that would be considered eligible for commuter slots under the new rules have gotten slots in the past from the scheduled airlines' committee.