Colorado

The accident involved 2 Swearingen airplanes. The pilot of the first airplane reported that he had taxied north for departure. There were several company aircraft in front of him in line for departure so he came to a complete stop. The pilot of the second airplane reported that he was also taxiing north for departure. He had seen the lights from an aircraft holding short of runway 17R; however, he did not see the lights of the first airplane until it was too late. The pilot of the second airplane reported he applied full brakes and used reverse thrust but was unable to avoid hitting the first airplane. Both airplanes were substantially damaged.

According to the pilot, he was told to enter left base and was cleared to land. The pilot stated that, when he reduced the airspeed to lower the landing gear, he "heard the gear come down," and he verified "three green in the [landing] gear indicator." He landed the airplane on its "main [landing gear] wheels first" and slowly let the nose of the airplane drop. Although both main landing gear assemblies remained down and locked, the nose landing gear collapsed, allowing the nose of the airplane and both propellers to strike the runway. The airplane slid approximately 3,000 feet, coming to a stop on the right edge of the runway. Several fractured propeller pieces impacted the left and right sides of the fuselage substantially damaging two fuselage station bulkheads. The fuselage bulkhead, forward of the nose landing gear well, was also substantially damaged due to contact with the runway. The pilot said that, during the approach, from base to final, he did not hear a landing gear warning horn. An air traffic control specialist, stated that he told the pilot to enter a left base and that he was cleared to land. The specialist stated that he observed the airplane roll out on a 2-mile final "with the gear down." As the airplane was rolling down the runway the "nose wheel collapsed." An FAA inspector examined the airplane and noted that, according to the Fairchild SA226 Maintenance Manual, the nose landing gear's up-lock mechanism was not properly lubricated, a "critical clearance" measurement between the nose landing gear's bell crank roller and positioning cam was found to be out of tolerance, and when the throttles were retarded, the landing gear warning horn activated, but it was "barely audible." According to the Fairchild SA226 Maintenance Manual, the landing gear should be lubed every 200 hours. The FAA inspector stated that the approved maintenance inspection sheet for the operator, did not show the requirement for the main landing gear or nose landing gear to be lubed every 200 hours.

The flight was following a heavy jet on landing approach. The crew agreed to fly the approach at a slightly higher altitude than normal to avoid any possible wake turbulence. The first officer, who was flying the airplane, called for the landing gear to be lowered. When the captain placed the gear handle in the DOWN position, he noted red IN-TRANSIT lights. He recycled the landing gear, but got the same result. He consulted the emergency checklist and thought he had manually extended the landing gear because he "heard the normal 'clunk feel' and airspeed started to decay." In addition, when power was reduced to FLIGHT IDLE, the GEAR UNSAFE warning horn did not sound. The first officer agreed, noting 2,000 pounds of hydraulic pressure. The airplane landed wheels up. Propeller blade fragments penetrated the fuselage, breaching the pressure vessel. Postaccident examination revealed the nose gear had been partially extended but the main landing gear was retracted. The crew said the GEAR UNSAFE indication had been a recurring problem with the airplane. The problem had previously been attributed to a frozen squat switch in the wheel well.

The pilot reported that he maneuvered for a left hand downwind leg for landing from the east to west. The pilot set up his downwind leg at 8,400 feet mean sea level putting him at what would have been 1,000 feet above the airport elevation of 7,411 feet. The pilot reported it was very dark and he could see the airport, but could not see the terrain. The pilot reported that suddenly he saw the ground. The airplane impacted the terrain and came to rest. The pilot reported that the airplane was experiencing no malfunctions prior to the accident. The airplane accident site was on the snow-covered edge of a mountain ridge at an elevation of 8,489 feet. An examination of the airplane's systems revealed no anomalies. Published terminal procedures for the runway indicated high terrain of 8,739 feet south-southeast of the airport. The published airport diagram for the airport directs right traffic for the pattern to runway 27.

A Piper PA-31T "Cheyenne" and a Cessna 172P "Skyhawk" collided in midair during cruise flight at dusk and in visual meteorological conditions. The Cheyenne departed under visual flight rules (VFR) from a local airport northwest of Denver, and was proceeding direct at 7,800 feet to another local airport south of Denver. Radar indicated its ground speed was 230 knots. Its altitude encoder was transmitting intermittently. The Skyhawk departed VFR from the south airport and was en route to Cheyenne, Wyoming, at 7,300 feet. The pilot requested and was cleared to climb to 8,500 feet and penetrate class B airspace. Radar indicated its ground speed was 110 knots. The Skyhawk was flying in the suggested "VFR flyway"; the Cheyenne was not. When the controller observed the two airplanes converging, he asked the pilot of the Cheyenne for his altitude. He replied he was at 7,600 feet. The controller immediately issued a traffic advisory, but the pilot did not acknowledge. Both airplanes departed controlled flight: the Skyhawk struck a house, and the Cheyenne fell inverted into the backyard of a residence. Wreckage was scattered over a 24 square block area in west Denver. At the time of the accident, the controller was handling low altitude en route, arrival and departure traffic for both airports. Wreckage examination disclosed four slashes, consistent with propeller strikes, on top of the Cheyenne's right engine nacelle, the cabin above the right wing trailing edge, the empennage at the root of the dorsal fin, and at the tail cone. The Cheyenne was on a similar flight three days before the collision when the pilot was informed by air traffic control that the transponder was operating intermittently. According to recorded radar and voice communications from that flight, the transponder/encoder operated intermittently and the pilot was so advised. Examination of the Cheyenne's altimeter/encoder revealed a cold solder connection on pin 8 of the 15-pin altimeter connector. When the wire was resoldered to the pin, the information from the altimeters, encoder, and altitude serializer was normal.

The pilot reported to Denver Air Route Traffic Control Center (ZDV) that his left engine had an oil leak and he requested to land at the nearest airport. ZDV informed the pilot that Akron (AKO) was the closest airport and subsequently cleared the pilot to AKO. On reporting having the airport in sight ZDV terminated radar service, told the pilot to change to the advisory frequency, and reminded him to close his flight plan. Approximately 17 minutes later, ZDV contacted Denver FSS to inquire if the airplane had landed at AKO. Flight Service had not heard from the pilot, and began a search. Approximately 13 minutes later, the local sheriff found the airplane off of the airport. Witnesses on the ground reported seeing the airplane flying westbound. They then saw the airplane suddenly pitch nose down, "spiral two times, and crash." The airplane exploded on impact and was consumed by fire. An examination of the airplane's left engine showed the number 2 and 3 rods were fractured at the journals. The number 2 and 3 pistons were heavily spalded. The engine case halves were fretted at the seam and through bolts. All 6 cylinders showed fretting between the bases and the case at the connecting bolts. The outside of the engine case showed heat and oil discoloration. The airplane's right engine showed similar fretting at the case halves and cylinder bases, and evidence of oil seepage around the seals. It also showed heat and oil discoloration. An examination of the propellers showed that both propellers were at or near low pitch at the time of the accident. The examination also showed evidence the right propeller was being operated under power at impact, and the left propeller was operating under conditions of low or no power at impact. According to the propeller manufacturer, in a sudden engine seizure event, the propeller is below the propeller lock latch rpm. In this situation, the propeller cannot be feathered. Repair station records showed the airplane had been brought in several times for left engine oil leaks. One record showed a 3/4 inch crack found at one of the case half bolts beneath the induction manifold, was repaired by retorquing the case halves and sealing the seam with an unapproved resin. Records also showed the station washed the engine and cowling as the repair action for another oil leak.

The airplane was maneuvering to deliver fire retardant when its left wing separated. Aircraft control was lost and the airplane crashed into mountainous terrain. A witness on the ground took a series of photographs that showed the air tanker's left wing separating at the wing root and the remaining airplane entering a 45-degree dive to the ground in a counterclockwise roll. An examination of the airplane wreckage revealed extensive areas of preexisting fatigue in the left wing's forward spar lower spar cap, the adjacent spar web, and the adjacent area of the lower wing skin. The portion of the wing containing the fatigue crack was obscured by the retardant tanks and would not have been detectable by an exterior visual inspection. An examination of two other air tankers of the same make and model revealed the area where the failure occurred on the accident airplane was in a location masked by the airplane's fuselage construction. The airplane was manufactured in 1945 and was in military service until 1956. It was not designed with the intention of operating as a firefighting airplane. In 1958, the airplane was converted to civilian use as an airtanker and served in that capacity until the time of the accident. The investigation revealed that the owner developed service and inspection procedures for the airtanker; however, the information contained in the procedures did not adequately describe where and how to inspect for critical fatigue cracks. The procedures were based on U.S Navy PB4Y-2 airplane structural repair manuals that had not been revised since 1948.

The pilot was flying a three leg IFR cross-country, and was on an ILS approach in IMC weather conditions for his final stop. Radar data indicated that the pilot had crossed the final approach fix inbound and was approximately 3 nm from the runway threshold when he transmitted that he had "lost an engine." Radar data indicates that the airplane turned left approximately 180 degrees, and radar contact was lost. A witness said "the airplane appeared to gain a slight amount of altitude before banking sharply to the left and nose diving into the ground just over the crest of the hill." Postimpact fuel consumption calculations suggest that there should have been 50 to 60 gallons of fuel onboard at the time of the accident. Displaced rubber O-ring seals on two Rulon seals in the left fuel valve and hydraulic pressure/deflection tests performed on an exemplar fuel valve suggest that the fuel selector valve was in the auxiliary position at the time of impact. The airplane's Owner's Manual states: "The fuel selector valve handles should be turned to LEFT MAIN for the left engine and RIGHT MAIN for the right engine, during takeoff, landing, and all emergency operations." No preimpact engine or airframe anomalies, which might have affected the airplane's performance, were identified.

The airplane was on a non-scheduled cargo flight which was projected to fly an approximate 240 degree course for 92 nm. The accident site was located on a heavily forested steep mountain side, 15 to 16 nm north of the airplane's projected course. The debris field began at an east-west ridge line, and progressed for 300 feet on a 010 degree track to the downed airplane. Examination of the airframe and engines revealed no evidence of preimpact discrepancies. The accident site was in an area where the Fall color of the aspens was at its peak. Additionally, it was an area where elk were sometimes observed.

The pilot obtained a weather briefing, filed an IFR flight plan, and departed on a nonscheduled domestic cargo flight, carrying 270 pounds of freight. The flight proceeded uneventfully until it was established on the VOR/DME-C approach. Radar data indicates that after turning inbound towards the VORTAC from the DME arc, the airplane began its descent from 10,600 feet to the VOR crossing altitude of 9,200 feet. Enlargement of the radar track showed the airplane correcting slightly to the left as it proceeded inbound to the VORTAC at 9,400 feet. Shortly thereafter, aircraft track and altitude deviated 0.75 miles northwest and 9,700 feet, 0.5 miles southeast and 9,600 feet, and 0.5 miles northwest and 9,400 feet before disappearing from radar. Witnesses said the weather at the time of the accident was 600 foot overcast, 1.5 miles visibility in "misting" rain that became "almost slushy on the ground," and a temperature of 36 degrees Fahrenheit. One weather study indicated "an icing potential greater than 50% and visible moisture" in the accident area. Another report said "icing conditions were likely present in the area of the accident." The airplane was equipped and certified for flight into known icing conditions. The wreckage was found in a closely area. There was no evidence of pre-impact airframe, engine, or propeller malfunction/failure. The pilot was properly certificated, but his flight time in aircraft make/model was only 38 hours. He had previously recorded 16 icing encounters, totaling 11.2 hours in actual meteorological conditions. He recorded no ice encounters and only 1.0 hour of simulated (hooded) instrument time in the Cessna 208. Microscopic examination of annunciator light bulbs revealed the GENERATOR OFF light was illuminated. This condition indicates a generator disconnection due to a line surge, tripped circuit breaker, or inadvertent switch operation. The operator's chief pilot agreed, noting that one of the items on the Before Landing Checklist requires the IGNITION SWITCH be placed in the ON position. The START SWITCH is located next to the IGNITION SWITCH. Inadvertently moving the START SWITCH to the ON position would cause the generator to disconnect and the GENERATOR OFF annunciator light to illuminate. He said this would be distracting to the pilot.