Curtiss C-46F accident at Near Fish Haven, Idaho, 7 Jan 1953

Accident narrative

On January 7, 1953, at approximately 0412 Mountain Standard Time, an Associated Air Transport Curtiss C-46F crashed about eight miles west of Fish Haven, Idaho. The aircraft, operating a military charter flight from Seattle, Washington, to Fort Jackson, South Carolina, was completely demolished. All 40 persons aboard—37 military passengers and a crew of three—lost their lives.

### The Flight

Trip 1-6-G4A departed Boeing Field in Seattle at 0050, with a scheduled first stop in Cheyenne, Wyoming. The crew consisted of Captain Lawrence B. Crawford, First Officer Maxwell F. Perkins, and Stewardess Marie Davis. Both pilots were well qualified on the C-46 and familiar with the route.

At departure, the aircraft weighed 45,401 pounds, which was 401 pounds over the maximum allowable gross weight, though the load distribution was within prescribed center of gravity limits. Prior to departure, the United States Weather Bureau briefed the crew on en route conditions, forecasting scattered to broken clouds to overcast. The briefing included a forecast of icing conditions in clouds and precipitation above 6,000 feet, with cloud tops ranging from 10,000 to 14,000 feet.

The flight proceeded on an Instrument Flight Rules plan at a requested cruising altitude of 13,000 feet. Routine position reports were made along the route with no mention of any irregularities. The last contact was at 0358, when the flight reported over Malad City, Idaho, at 13,000 feet and estimated reaching Rock Springs at 0445. When no further radio contacts were received, a widespread search began.

### What the Investigation Found

Five days later, a Civil Air Patrol pilot sighted the wreckage. Extremely deep and heavily drifted snow prevented a detailed examination of the wreckage and the recovery of bodies until June.

Investigators determined that the aircraft initially struck a small pine tree 45 feet south of an 8,500-foot east-west ridge. The airplane was traveling on a heading of about 30 degrees in a nearly level longitudinal attitude. It continued through several trees before disintegrating as it traveled down a 50-degree slope. Impact-stopped watches placed the time of the crash at approximately 0412.

Examination of the scattered wreckage yielded no evidence of structural or mechanical difficulty, fire, or explosion before impact. Both engines were rotating, and the propellers were in the cruising r.p.m. range, indicating power was being developed. The relatively flat angle of the initial impact indicated the crew had partial control of the aircraft. Two oxygen bottles were recovered with their main valves closed, showing there had been no shortage of oxygen.

The aircraft's deicing equipment was found to have been operative three days before the accident, and there was an ample supply of alcohol for the propellers and carburetors. During the initial observation of the wreckage, investigators noted a strip of hard ice adhering to the leading edge of a partially exposed wing deicer boot. The ice was about three feet long, 1.5 inches thick, and blunt at both ends. The Board noted strong indications that this ice had accumulated during descent, forming so rapidly that the action of the boots could not completely break it off.

Weather analysis indicated that at 13,000 feet between Malad City and Bear Lake, the flight would have encountered light rime ice and light to moderate turbulence in the cloud tops. Another flight preceding the C-46 by only a few minutes flew through this area without difficulty and avoided turbulence by climbing 500 feet. The Board noted that no request for a higher altitude was received from the Associated Air Transport crew.

Below the cruising altitude, westerly winds lifting moist air over the 8,000- to 9,000-foot mountains produced zero ceilings, moderate to severe turbulence, moderate to heavy icing, and snow. Ground observers in the area described the conditions as a blizzard.

The Board considered it likely that an involuntary descent was made into this area of worsening ice and turbulence. The elapsed time and distance from Malad City indicated the aircraft's ground speed had dropped to about 180 m.p.h., which the Board presumed was due to a required speed reduction for turbulence. The aircraft ultimately struck the terrain on a heading almost 100 degrees from its intended course. This gave rise to the Board's belief that a rapid accumulation of ice on the wings during the descent would have seriously impaired lift and adversely affected controllability, preventing the airplane from maintaining altitude even with maximum continuous power.

The Board noted that the 401-pound overweight condition at departure was not pertinent, as fuel consumption meant the aircraft weighed about 3,000 pounds less than its takeoff weight at the time of the crash.

### Probable Cause

The Board concluded that the aircraft encountered severe turbulence and heavy icing which precipitated its descent, though the reason for the initial descent was not known.

The Board determined that the probable cause of the accident was "the inadvertent descent into an area of turbulence and icing which resulted in the flight's inability to regain a safe altitude."