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1/2 mile visibility or 2,400 feet Runway Visual Range (RVR).[1]
The USWB at Los Angeles International Airport recorded a local weather observation of 2340, approximately at the time Flight 221 was inbound from the outer marker. This observation was: Sky partially obscured; surface visibility 3/4 mile, tower visibility 1/2 mile, ground fog and smoke; tempera- ture 47°F., wind south-southwest 4 knots, altimeter setting 30.11 inches. In the remarks section of this observation the following was recorded: Runway 251 visual range 5,000 feet, runway 07 runway visibility less than 3/16 of a mile, runway 24 runway visibility less than 3/16 of a mile runway 06 runway visibility less than 3/16 of a mile, fog obscuring 4/10 of the sky, surface visibility 3/4 of a mile.
The USWB transmissometer record indicated that the RVR for runway 25L went below 6,000 feet at approximately 2338. From 2340 to 2345 the RVR varied between 5,000 and 6,000 feet. At 2347, six minutes after the accident occurred it dropped to less than 1,000 feet.
Tire marks and propeller slash marks made by N93131 were found on runway 251 as was the No. 2 engine nose case and propeller assembly. The initial impact tare marks, made by the left main landing gear outboard tire started at a point 5,430 feet beyond the displaced threshold and 14 feet 10 inches from the south edge of the runway. This mark was heavy at the beginning and continued for approximately 167 feet gradually decreasing until the mark disappeared completely. The inboard tire of the left main gear touched down 2 feet 7 inches beyond the outboard tire and left a moderate mark for 14 feet. Tire marks from the right main landing gear were found approximately 57 feet beyond the initial impact point of the left main landing gear. These marks continued for approximately 17 feet.
10/ RVR is an instrumentally derived value that represents the horizontal distance a pilot will see down the runway from the approach end, it is based on the sighting of either high-intensity runway lights or on the visual contrast of other targets, whichever yields the greatest visual range.
- ↑ RVR is an instrumentally derived value that represents the horizontal distance a pilot will see down the runway from the approach end, it is based on the sighting of either high-intensity runway lights or on the visual contrast of other targets, whichever yields the greatest visual range.
The primary instrument used to determine RVR is the transmissometer.
It consists of a projector, a detector, and a meter to indicate the transmission of light through the atmosphere. The projector directs a steady light beam of constant intensity toward a photoelectric detector a known distance away. The intensity of the light received at the detector is dependent on the degree to which the path between the projector and detector 1s obstructed by atmospheric conditions. It is measured by the detector as a percentage of the amount of light that would be received in a clear atmosphere. A meter converts this trans- missivity into a measure of visibility which is extrapolated into RVR values of up to 6,000 feet.
