Background
Flight 327 was scheduled from Providence, Rhode Island, to Tulsa, Oklahoma, with intermediate stops including Chicago, Illinois; St. Louis, Springfield, and Joplin, Missouri. The flight to Chicago was routine. However, after securing the cockpit, the crew observed that the fire-warning light for the forward cargo and electrical accessory compartments flickered. This was reported to both ground crew and the relieving crew during a routine crew change, and was recorded in the aircraft log. Due to necessary repairs, the flight was delayed 1 hour, 40 minutes, departing Chicago at 1950. The new crew consisted of Captain Wesley G. Mims, First Officer Paul H. Johnson, and Stewardess Shirley D. Walker.
Flight to Joplin and Departure
The flight was routine to Joplin, departing at 2323 with seven passengers aboard. The aircraft weighed 35,940 pounds, well under the allowable gross takeoff weight, with properly distributed load. The flight was cleared by Air Route Traffic Control (ARTC) to the Owasso “H” facility via airway V-88 to maintain 4,000 feet, and to contact Tulsa approach control on crossing the south course of Chanute low frequency range for further clearance.
At approximately 2333, 10 minutes after takeoff, ARTC advised the flight to climb to 4,500 feet and to report leaving 4,000 feet. This was acknowledged, and Flight 327 reported leaving 4,000 feet at 2334. Approximately 10 minutes later, company radio at Tulsa gave the flight the 2328 weather sequence and the local altimeter setting of 30.15, with field pressure at 460 feet above zero. The flight acknowledged and reported switching to Tulsa approach control frequency.
Approach and Descent
At 2347, the flight reported crossing the south leg of the Chanute low frequency range and was cleared by approach control direct to Owasso, to descend to and maintain 3,500 feet, and to report when over Owasso. The 2328 Tulsa weather was reported as measured ceiling 600 feet, overcast; visibility 2-1/2 miles; very light drizzle and fog; wind calm. Later, the flight reported it was 1-1/2 minutes from Owasso and asked about potential delays. Approach control advised no delay as the only local traffic was making an ILS approach. Shortly after, approach control advised the flight that visibility was then 1-3/4 miles and asked if an Owasso approach straight in to runway 17 or an ILS approach was preferred. The flight chose the Owasso approach and was cleared at 2357, asked to report over Owasso inbound.
At 2400, Flight 327 reported over Owasso, inbound, and was cleared to land on runway 17L. Two minutes later, a special 2355 weather observation was transmitted: measured 200 feet overcast; visibility 1-3/4 miles; very light drizzle and fog. This transmission was not acknowledged, and nothing further was heard.
Probable Cause
The Board determined that the probable cause of this accident was the captain's lack of alertness in allowing the first officer to continue an instrument descent to an altitude too low to permit terrain clearance. The following findings were reported: This flight was the first time the captain and first officer had flown together; the first officer flew the aircraft from Joplin and during the instrument approach; the aircraft and its components, including altimeters, functioned normally throughout; the last weather report indicated rapidly deteriorating conditions; the captain told the first officer he could descend to 700 feet, without specifying mean sea level or above the airport elevation; the captain allowed the aircraft to be flown below the company’s approved landing minimums for this type approach and to an altitude precluding terrain clearance.