Accident at Chillicothe, Missouri, 3 Aug 1976 (N1553W)

Accident narrative

On August 3, 1976, at about 2116 central daylight time, a Beechcraft Baron 58 crashed shortly after takeoff from the Chillicothe Municipal Airport in Chillicothe, Missouri. The pilot and all five passengers were killed, and the aircraft was destroyed by impact and a post-crash fire.

### The flight

The aircraft, registration N1553W, was operated by Rupp Automotive, Inc. as a noncommercial passenger flight to Kansas City, Missouri. The 44-year-old pilot held a commercial certificate and had accumulated 2,283 total flight hours, including 2,012 hours in multi-engine aircraft and 1,136 hours as pilot-in-command in the Baron 58.

At 1658, the pilot filed an instrument flight rules flight plan, estimating a 2100 departure and a 20-minute flight time. Because Chillicothe Airport had no air traffic control facilities, he intended to activate the flight plan after departure. The night sky was dark but clear, with visibility of about 15 miles and light winds from the south.

Witnesses saw the pilot taxi to the approach end of runway 14 at about 2110, stop on the taxiway to perform pretakeoff checks, and begin the takeoff roll at 2115. The aircraft took off with no apparent problems. One witness saw the airplane climbing normally 100 to 150 feet above the runway before his attention was momentarily diverted. Hearing a popping sound, he looked back and saw a ball of fire east of the airport. The aircraft had crashed about a quarter-mile east-southeast of the departure end of the runway.

### What the investigation found

The aircraft struck the ground in a right wing-low and slightly nose-low attitude. The landing gears were extended and the wing flaps were retracted. The flight control cables were intact. The rudder was in the full right position, and the control wheel was rotated fully right.

The aircraft's estimated gross weight at takeoff was 5,496 pounds, slightly over its maximum certificated gross weight of 5,400 pounds. The Board noted this overweight condition would have degraded single-engine climb performance by about 30 feet per minute, but would not have significantly affected the aircraft's performance.

Examination of the engines revealed that the left engine's crankshaft had broken at the No. 7 crankcheek. The camshaft was also broken in two locations. The left propeller had broken from the engine crankshaft, with one blade buried almost perpendicularly in the ground. Its chord line was aligned with the aircraft's impact heading, and the ground was not disturbed in a way suggesting the blade twisted after impact. The blade counterweights indicated a nominal blade angle of 21 degrees.

The right engine was intact except for a forward portion broken off with the propeller. The right propeller's counterweights indicated a nominal blade angle of 14 1/2 degrees. The Board believed it was turning at a relatively high rpm at impact but not under full power, suggesting the pilot probably reduced power on the right engine shortly before impact in an effort to control the aircraft laterally and directionally.

Metallurgical examination of the left crankshaft showed the fracture was a fatigue crack originating below the forward radius of the No. 3 main bearing journal. No material defects were found. The Board believed the crack was probably initiated by a combination of residual stresses introduced during manufacturing and normal or abnormal operating stresses.

Flight tests in a similar Baron 58 demonstrated that with the landing gear down, flaps up, and the left engine shut down at the normal takeoff speed of 102 mph, the airspeed decayed to 90 mph in 5.2 seconds. A descent rate of 100 to 200 feet per minute was needed to maintain 102 mph. The aircraft's performance charts indicated it could climb about 300 feet per minute at 117 mph with one engine inoperative, its propeller feathered, and the landing gear retracted. However, with the landing gear extended and the propeller windmilling, climb performance was degraded by a total of 400 feet per minute.

The Board concluded that the left engine failed when the aircraft was between 50 and 100 feet above the runway. The pilot probably was distracted by the failure and did not retract the landing gear. The Board believed the left propeller probably feathered automatically after the camshaft broke and disrupted the oil supply to the propeller governor, but during the several seconds before this occurred, the windmilling propeller would have produced significant drag.

Because the aircraft struck the ground with considerably more force than a 100-foot-per-minute descent would generate, the Board concluded that the pilot stalled the aircraft in an attempt to maintain altitude and avoid the ground. The pilot's ability to maintain flight was marginal due to the nighttime conditions, the low altitude, and the aircraft's inability to climb or maintain level flight in the takeoff configuration with an inoperative engine and windmilling propeller.

### Probable cause

The National Transportation Safety Board determined that the probable cause of this accident was "the sudden failure of the airplane's left engine at a point on the takeoff flightpath where the airplane's single-engine performance in the takeoff configuration and its height above the ground combined to make the pilot's ability to sustain flight marginal. The pilot's failure to retract the landing gear and control the airplane to maintain a safe airspeed contributed to the accident and were factors in causing the high acceleration loads when the airplane struck the ground."