Page:CAB Accident Report, Mid-Air Collision on 30 September 1959.pdf/4

Rh The tower was equipped with a portable traffic light (Aldis lamp) which is directional and emits an intense, narrow beam of light. The color of the light (white, green, or red) is controlled by the Operator through a system of levers and triggers in the two handles. Signals may be discernible to the pilot of any aircraft visible to the tower operators and to which the light is directed.

A small extension from the lamp glows when the light is actuated by a trigger, indicating that the light is operating. The tower controller could not remember whether he saw this indication when he directed the light toward the Aeronca. However, he stated the light did function correctly when checked immediately following the accident.

The disadvantages of the use of the light are that the pilot cannot constantly look at the control tower while flying his airplane and could inadvertently miss a signal directed toward him; the information transmitted by the light signal is limited; and no accurate sighting device is provided.

There was conflicting testimony between the North Philadelphia Control Tower operators and pilots who fly nonradio aircraft as to whether preventive control was in effect at the airport. "Preventive Control" applies at locations which have locally based squadrons or groups of military aircraft, or local civilian operators, or schools such as North Philadelphia Airport. In such cases mutual agreements and arrangements must be made with the responsible heads of these groups prior to the inauguration of preventive control. Such control is not to be employed for transient aircraft.

No evidence could be found to indicate that an agreement or prearrangement had been made in accordance with Section 3.700 of the ANC Manual between the North Philadelphia Airport Control Tower and the Civil Air Patrol, or between the tower and the civilian flying school based at the airport, as related to the use of negative or "preventive control." Nevertheless, several witnesses, including the FAA Supervising Inspector of the Philadelphia General Safety District Office, stated it was the practice at North Philadelphia Airport for nonradio—equipped aircraft to continue an approach and land without light communications. In the absence of radio communications or any light signal, any aircraft may land or take off at any airport without prior approval.

Although it is recognized that there was conflicting evidence as to the positions of the aircraft in the traffic pattern, the Board believes that the actual positions of the aircraft were as follows: The Cessna entered the landing pattern behind, to the right of, and below the Aeronca. The Aeronca pilot could not have seen the Cessna without looking back to his right and down. This is quite unlikely since his attention would have most likely been directed to the airport and runway which was to his left as he flew the downwind and base leg.