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It is believed that the captain knew the reported weather conditions to the extent indicated to him by the GCA controller. It must be assumed that he was monitoring his altimeter and knew that when he passed through his minimum altitude if he had not established visual reference to the airport or ground, or if he had been advised by GCA that he was exceeding the safety limits, he would have had to execute the required missed-approach procedure. Since he did not execute the procedure, did not question the condition of the weather, and since he was not advised by GCA to abandon his approach upon reaching a critically low altitude, it is assumed that he had visual contact with the runway and was contemplating a successful landing.
The controller stated in his testimony that he saw the aircraft target over the end of the runway. However this target return must have been from part of the wreckage which continued up the runway from the point of impact.
The six pairs of red approach lights, two of the green threshold lights, and the first four pairs of runway lights beyond the two operating threshold lights were not lit. The single strobe light was lit; however its beam was directed 4-1/2 degrees above the glidepath angle of three degrees. As an aircraft goes below the beam of the strobe light, the effectiveness of the light is greatly reduced. For example, at a point 50 feet below its directed beam, the effective strength of the beam is reduced by as much as 75 percent.
The captain could not have known that the approach lights and some of the threshold and runway lights were inoperative since this information had not been given to him. It is also believed that he would not have flown below his minimum altitude had he not had some portion of the runway lights in sight. The Board concludes, however, that the existing lighting situation was a factor in causing the captain to improperly orient himself along the runway. The Board further concludes that the captain knew he was below the glidepath throughout the approach but did not believe it to be critical.
It should be noted that although the approach procedure was flight-checked and approved by the Flight Standards Service of the Federal Aviation Agency, apparently no consideration was given to the fact that the AN/FPN-33 is not deemed suitable by the Aviation Research and Development Service, the Aviation Facilities Service, or the Air Traffic Service of FAA for use as an FAA-operated air traffic control facility. Another significant point to be noted is that the Flight Standards Service, in its flight checks of the facility, utilized a lower-limit safety zone line which extended one and one-half degrees below the center of the glidepath. The Air Traffic Service has established, for facilities under its jurisdiction, a safety zone limit of one-half of one degree under the center of the glidepath. A displacement value of 40 feet below glidepath at one mile, therefore, would not be considered alarming by the controller operating under the concept of a one and one-half degree safety zone, whose lower limit at that point would be 159 feet below center of glidepath; whereas, were the controller utilizing the standards prescribed by the Air Traffic Service, he would be commencing to take action to order a pullup and missed approach procedure to be executed had the aircraft deviated to the extent indicated. However, a finite value in feet cannot be estimated accurately on a radar scope with the type of presentation provided for the AN/FPN-33. For this reason, the military services have instructed their controllers from the practice of providing foot values of displacement from centerlines of azimuth
