Page:CAB Accident Report, Northwest Airlines Flight 2.pdf/9

Rh the time of the accident construction work was in progress, necessitating the closing of the field except for the northwest-southeast runway. The day preceding the accident, the surfacing of the northeast-southwest runway had been laid and rolled. It was probably in a usable condition but had not been officially opened.

Weather Conditions

The weather conditions in the vicinity of Bismarck for several hours prior to the accident and until 7:05 p.m., when broken clouds were reported, were substantially as reported by radio to Captain DeLong. The ceiling ranged from 3000 to 3600 feet except for a short period during the heaviest part of a thunderstorm, during which time the ceiling lowered to 2500 feet. Visibility at the time of the accident was about two miles, and the surface winds which had been north-northwest from 4:30 p.m. to 6:01 p.m. shifted to north-northeast at about 6:10 p.m., and increased rapidly in velocity, holding between 10 and 60 degrees, velocity 20 to 25 m.p.h., and gusty. This was approximately 18 minutes prior to the landing of Trip 2. Local winds varied from northeast to northwest as the storm approached, and shifted back to northeast, accelerating the velocity and producing gustiness, as the thunderstorm passed to the north of Bismarck. According to the U. S. Weather Bureau airway observations, the wind velocity never exceeded 30 m.p.h.

The cup anemometor will not register an instantaneous change in velocity during gusts or lulls, but indicates more correctly the average wind velocity in miles per hour. The range between gusts and lulls is