Curtiss C-46F accident at Fairbanks, Alaska, 30 Dec 1951

Accident narrative

On December 30, 1951, at approximately 2207 Alaskan Standard Time, Transocean Air Lines Flight 501 South, a Curtiss C-46F, struck Chena Dome near Fairbanks, Alaska. The accident occurred during an attempted orientation on the Fairbanks radio range preparatory to landing at Ladd Field. The two pilots and two passengers were killed, and the aircraft was demolished upon impact.

### The flight

Transocean Air Lines was operating the flight under a contract with the United States Navy. The aircraft departed Point Barrow at 1655 on an IFR flight plan to Fairbanks. The crew consisted of Captain R. R. Warren and First Officer R. V. Irwin. Following an en route stop at Umiat, the flight departed at 1950 with a takeoff gross weight of 36,373 pounds. The only passengers aboard were two Wien Alaska Airlines employees traveling nonrevenue.

Weather forecasts for the route indicated instrument and on-top flight conditions, with winds from 20 degrees at 40 to 60 knots to the Nenabank intersection, and 240 degrees at 30 to 40 knots from there to Fairbanks. An instrument approach was anticipated at Fairbanks.

Captain Warren had 7,034 flying hours, including 150 in C-46 equipment. Records indicated he had previously failed written and flight examinations for an airline transport rating, demonstrating below-average ability in certain phases of instrument work. He successfully met the requirements in November 1951, demonstrating above-average ability on cone identification but below-average ability on ADF (Automatic Direction Finder) tracking. First Officer Irwin had 2,552 flying hours and had also passed his airline transport rating flight test in November 1951.

### Sequence of events

The flight reported over Bettles at 2053. At 2144, the crew reported 25 miles northwest of the Nenabank intersection, estimating the intersection at 2150. Air Route Traffic Control cleared the flight to the Fairbanks radio range station, instructing it to cruise and maintain 8,000 feet to Nenabank, and then 5,000 feet to Fairbanks.

At 2148, the flight reported over Nenabank at 8,000 feet, descending to 5,000 feet IFR, and estimating Fairbanks at 2200. The flight reported reaching 5,000 feet at 2155. At 2157, it was cleared for a standard range approach to Fairbanks, to cross the station at 4,000 feet.

At 2205, the flight advised Fairbanks: "ADF OUT HAVE MISSED CONE PROCEEDING OUT WEST LEG WILL CALL WHEN OVER STATION." Fairbanks requested confirmation that the flight was proceeding out the west leg, which the pilot confirmed at 2207. This was the last message received, and it is believed the aircraft crashed immediately thereafter.

### What the investigation found

Severe cold weather, with temperatures as low as 70 degrees below zero, delayed search activities. The wreckage was sighted on January 3, 1952, and reached by a USAF helicopter on January 5. The aircraft had struck the snow-covered area near Chena Dome at approximately 1,550 feet mean sea level on a magnetic heading of about 20 degrees. A recovered wrist watch had stopped at 2207:07.

When weather permitted a Civil Aeronautics Board investigator to reach the scene in June 1952, he determined that the aircraft was flying straight and level at impact. The left wing panel made first contact with the steep slope and was torn from the fuselage. The fuselage was found inverted at the crest of the mountain. Both engines and propellers were located and bore evidence that power was being developed at impact. The control systems revealed no evidence of malfunction, and there was no evidence of fire. The ADF tuning dial was tuned to the Fairbanks radio range frequency.

Meteorological data indicated the flight likely encountered light turbulence, possibly light rime ice, and high wind velocities reaching a maximum of 60 knots from the southwest. Another Transocean flight over the same route 50 minutes earlier reported that precipitation static and St. Elmo's fire made it impossible to receive the Nenana radio range station. However, ground radio facilities were monitored and found to be operating normally.

Radar plots of Flight 501 South in the Fairbanks area revealed wide discrepancies from the crew's position reports. At 2144, when the crew reported being 25 miles northwest of Nenabank, radar placed the aircraft only 12 miles west of Fairbanks—about 60 miles southeast of their reported position. When the flight reported over Nenabank at 2148, radar indicated the aircraft was over or very near the Fairbanks range station. The radar target faded at 2157, showing the aircraft had turned left into a mountainous area. The Board noted there was no instrument procedure for the Fairbanks range that authorized such a left turn.

The Board analyzed the flight's progress and found that the 2148 position report would have required an unrealistic ground speed of 375 miles per hour. The Board concluded that the pilots confused their actual position with their reported position. Regarding the reported ADF failure, the Board stated it was possible the unit was not inoperative, but that the pilot rejected the needle's indication because he thought the flight was still west of the station. Even if the ADF had failed, the aircraft was equipped with two additional low-frequency receivers and a marker beacon receiver. The Board noted that intelligent and proper use of the radio equipment was not accomplished after passing Bettles, resulting in increasing confusion.

### Probable cause

The Board determines that the probable cause of this accident was the failure of the pilot to follow procedures and utilize properly the radio facilities for approach and letdown at Fairbanks, with the result that the flight became lost.