Accident Overview
On August 24, 2017, at about 1400 mountain daylight time, a Cessna 310I airplane, registration N8170M, was substantially damaged in an accident near Salt Lake City, Utah. The airline transport pilot sustained minor injuries. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as an aerial photography flight.
Sequence of Events
The pilot reported that after starting both engines, neither ran smoothly at idle. The left engine shut down when the throttle was reduced to idle but restarted easily. Both engines ran smoothly slightly above idle. The fuel mixture was leaned for taxi and runup, and exhaust gas temperatures were higher than usual. During the engine runup, the left engine again lost power at idle and was restarted. Propellers produced normal rpm loss when cycled, but engines ran rougher than expected during magneto checks, with about 200 rpm loss. The pilot advanced throttles and leaned mixtures to clear suspected carbon buildup on spark plugs, after which both engines ran smoothly at idle and magneto checks showed normal rpm loss.
During initial climb after takeoff, the pilot retracted landing gear and noticed the airplane did not accelerate normally. Reducing angle of attack did not help; both engines showed fluctuations in power, fuel flow, and rpm. The propeller and throttle levers were full forward, and the auxiliary fuel pump was set to high. The airplane decelerated and yawed left. The pilot banked right and feathered the left propeller, but the airplane continued descending. The pilot reduced mixture controls to idle-cutoff. The airplane impacted two power poles and the ground before skidding to a stop adjacent to a building. A postaccident fire ensued.
Postaccident Examination
The wreckage was relocated for examination. Propellers separated from engines. Upper engine cowlings were removed; interior surfaces of both upper and lower cowling halves were dirty. Engine exterior surfaces were clean and undamaged. Spark plugs from both engines had some electrodes with sooty deposits and others dark. The left engine’s tachometer generator was undamaged, but its cannon plug was not attached to the tachometer drive; plug and fitting were undamaged. Both engine-driven fuel pumps were removed; drive couplings and pumps were undamaged, and drive shafts rotated freely. No evidence of preexisting malfunctions or failures that would have precluded normal operation was found.
The electrical fuel boost pump system included pressure switches. Cockpit switches had three positions: LOW, OFF, and ON. In 1988, Service Bulletin MEB88-3 mandated removal of pressure switches and rewiring so switches directly control pumps in LOW and HIGH modes, with switches relabeled LOW, OFF, HIGH. In the accident airplane, switches had middle labeled OFF and upper labeled ON; both were found OFF. Pressure switches were still installed. Testing showed the left engine’s pressure switch stuck in "pressure" position.
The right fuel selector valve handle was between "Right" and "Off"; valve was in "Off". Left handle was in "Left". The alternate air door connection on the right engine was excessively worn.
Maintenance and Manual Information
Both engines were installed in August 2017 and had about 16 hours since overhaul. The airplane’s Owner’s Manual specified that the "Before Take-off" procedure included placing auxiliary fuel pump switches in "ON". The manual listed twin-engine climb performance at 5,000 ft msl, 41°F, and maximum gross weight (5,100 lbs) as 1,220 fpm, and 1,650 fpm at 4,300 lbs. Single-engine climb performance at same conditions and maximum gross weight was 155 fpm; at 4,300 lbs, it was 325 fpm.