Douglas DC-3C accident at Phoenix, Arizona, 21 Apr 1957 (N-65276)

Accident narrative

On April 21, 1957, at approximately 1344, a Frontier Airlines Douglas DC-3C, N 65276, struck a mountain ridge about 40 miles north of Phoenix, Arizona. The aircraft lost approximately 12 feet of the outer portion of its left wing but continued flight and landed safely at Phoenix. The 26 occupants were not injured.

### The flight

Flight 7 was a scheduled service between Denver, Colorado, and Phoenix, Arizona, with intermediate stops at Pueblo, Alamosa, and Durango, Colorado; Farmington, New Mexico; and Winslow, Flagstaff, and Prescott, Arizona.

At Farmington, a scheduled crew exchange was made. Under the company's scheduling method, crews flew to Farmington and returned to their respective departure points, while the aircraft continued to the scheduled destination. The new crew consisted of Captain Dale R. Welling, First Officer Herman B. Wrasse, and Stewardess Donna J. Bailey. Captain Welling had 13,679 flying hours, of which 8,371 were in DC-3 equipment. First Officer Wrasse had 1,946 flying hours, with 787 in the DC-3.

Prior to departing Phoenix that morning on a northbound flight, Captain Welling reviewed the available en route and terminal weather reports and forecasts. He filed a flight plan to fly visual flight rules (VFR) to Farmington and return to Winslow, and to fly instrument flight rules (IFR) for the remaining portion of the flight to Phoenix, with refueling planned at Prescott. This plan was approved by the company's dispatch office in Denver.

The flight to Farmington and the return to Winslow proceeded VFR as planned. At Winslow, based on his visual observation of existing weather conditions, the captain decided to continue VFR to Flagstaff and Prescott. Many of the en route stops, including Prescott, were "one-engine stops" where the crew did not leave the aircraft; weather information was taken to the aircraft by ground personnel.

The flight arrived at Prescott at 1316. Captain Welling stated that during the approach, he looked toward Phoenix and the weather in that direction appeared adequate for VFR flight. Upon landing, he informed the Denver dispatcher to change the flight plan from IFR to VFR to Phoenix and canceled the scheduled refueling.

Flight 7 departed Prescott at 1321, 11 minutes late. At takeoff, the aircraft's gross weight was 24,368 pounds, which was 978 pounds below the maximum allowable, and the load was properly distributed.

### The accident sequence

Following takeoff, the aircraft climbed to a cruising altitude of 6,500 feet. At 1335, approximately 35 miles from Prescott, the flight called the company's Phoenix office for the latest weather. They were given the 1330 report: 1,500 scattered, 3,000 broken, 10,000 overcast; visibility 12 miles; wind west 18 to 30 knots; light rainshowers.

At 1339, the flight acknowledged the message, stated it was approaching Knob intersection, and requested an Air Route Traffic Control (ARTC) clearance to Phoenix. Five minutes later, the company relayed the clearance: "ATC clears Frontier 7 from Knob intersection to Phoenix omni, maintain 7,000."

When the flight did not acknowledge the clearance, the radio operator called again. The flight replied: "Just hit a downdraft, declaring an emergency, changing to tower frequency."

According to the crew's testimony, they had flown beneath the overcast and free of clouds until nearing Rock Springs. The captain stated the overcast was lowering, the scattered clouds beneath them appeared to be forming a solid deck, and large cloud buildups were visible ahead. Because of this, they requested the IFR clearance and changed course to intercept Knob intersection, which allowed a lower altitude route.

The crew testified that immediately after receiving the clearance, they began climbing to 7,000 feet. As climb power was applied, the aircraft began to settle. Airspeed dropped from 130 to 115 knots, and a descent of approximately 1,000 feet per minute was observed. The captain stated that despite applying full open throttles and placing the propellers in full low pitch, the aircraft settled into a snow squall that seriously impaired visibility. The airspeed indicated 90 knots, and the mountain peak became hazily visible before the left wing struck the ground.

Captain Welling described the air as a "soggy airmass" and said the downdraft was not precipitous and caused little or no pressure against the seat belt. He was positive the flight did not enter clouds prior to the descent.

Following the impact, the aircraft staggered and rolled left. Power was reduced on the right engine and full right rudder was applied. With the return of full power to the right engine, the aircraft regained airspeed and slowly returned to level flight. Although aileron control was seriously restricted, the aircraft climbed to its assigned altitude. At 1400, the flight advised the company it had lost a portion of its left wing and aileron. The tower alerted emergency equipment, and the aircraft landed on runway 26 at 1405 without further incident.

### What the investigation found

The separated portion of the left wing was located at an elevation of 4,600 feet on the west ridge of a 5,000-foot mountain, approximately six miles east of New River, Arizona. The wreckage and terrain showed the left wing struck a small tree, large rocks, and a large cactus in a nose-up attitude.

The wing was sheared from station 286.4 outboard to the tip, and the separated pieces were crushed and twisted. The remaining left wing had deep span-wise compression wrinkles, and the damaged left aileron was locked in the neutral position, which limited the right aileron's travel to seven degrees up and two degrees down. All damage was confined to the left wing and aileron assembly. Maintenance records showed the aircraft was airworthy prior to departure, with no evidence of pre-impact failure.

The surface synoptic weather map for 0830 showed weak low centers over Oklahoma, Montana, and southern Nevada. By 1130, a distinct wind shift and temperature drop at Phoenix and Litchfield Park indicated a cold front was developing. Hourly reports showed this front passed Phoenix by 1130, Tucson by 1230, and Prescott by 1430, moving east-northeast. Forecasts available at Winslow indicated showery conditions, local thunderstorms, and moderate turbulence with moderate to heavy icing in the higher terrain. The Prescott forecast indicated a 2,500-foot overcast, 1,500 scattered, light rainshowers, and 20-knot winds.

Passenger and stewardess testimony varied decidedly from the crew's account. Passengers stated that the aircraft intermittently flew through clouds that completely obscured vision, and that four or five minutes prior to impact, the aircraft was flying in dense clouds. None sensed a downdraft or heard the application of additional power. Two passengers who were pilots also testified they did not hear any engine sound changes.

One passenger, a former Air Force pilot, testified he had landed his own airplane at Prescott that morning and decided to continue his trip on the airline because weather briefings indicated conditions between Prescott and Phoenix would be marginal for VFR flight. The stewardess testified she was standing in the aisle when the impact occurred and did not feel any sensation of a downdraft beforehand.

The company dispatcher in Denver testified that he realized weather conditions for the latter portion of the flight were marginal. However, he agreed to amend the flight plan because the captain had an on-the-scene observation of the weather. The Board noted that while dispatching is a joint responsibility, the dispatcher rarely countermanded or questioned the captain's decisions.

The Board noted that the 11-minute delay departing Prescott, combined with the time-consuming climb required for an IFR departure on the available airways, likely contributed to the captain's decision not to file an IFR flight plan. However, the Board found that the continuing rain at Prescott and the available weather information should have indicated that VFR flight would be extremely marginal. The company's flight manual and chief pilot instructed pilots to obtain an IFR clearance whenever marginal conditions were encountered; the Board found these instructions were disregarded.

The Board believed the passenger testimony that the aircraft intermittently flew through clouds and went on solid instruments several minutes before the crash. The Board also noted that the aircraft must have descended approximately 1,900 feet in the one minute between the clearance request and the emergency declaration. The Board found it unreasonable that the occupants would not have sensed a rapid descent of this magnitude or heard the application of full power. Furthermore, the low-level westerly winds crossing the mountain ridge were more likely to produce updrafts than downdrafts.

The Board concluded there was insufficient evidence to support a sustained downdraft condition and believed the aircraft was being flown at a dangerously low altitude over mountainous terrain. The Board also concluded that the company's dispatching system should be reevaluated to ensure dispatchers enjoy the status contemplated by regulations.

### Probable cause

The Board determines that the probable cause of this accident was the attempt by the pilot to fly over mountainous terrain by visual reference to the ground in weather conditions which severely restricted forward visibility and necessitated a descent to a dangerously low altitude.