C-GXKS

On August 1, 2020, about 1000 eastern daylight time, a Piper PA-31-325, Canadian registration C-GXKS, was substantially damaged when it was involved in an accident near Sumter, South Carolina. The pilot and copilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 aerial observation flight.

According to the pilot, he and the copilot had been flying mapping flights for the United States Geological Survey. The pilot stated that they had scanners weighing about 800 lbs on board and that they would fly about 300 ft above ground level in a grid pattern while mapping. He further stated that he personally fueled the inboard and outboard fuel tanks the day before the accident flight. On the accident flight, the pilot was seated in the right seat, and the copilot was seated in the left seat. They departed Santee Cooper Regional Airport (MNI), Manning, South Carolina about 0630 and planned on returning to the same airport. After 2 hours of flight time, the pilot, who was the pilot flying, switched from the inboard fuel tanks to the outboard fuel tanks. The pilot stated he did not verbalize to the copilot that he had switched the tanks. The pilot further stated the pilot flying will commonly request the other pilot to assist with the tank switching procedure since the tank selectors are behind the pilots’ seats and are not visible without looking behind and downwards.

About 1.5 hours later, while the copilot was flying, the left engine started “surging” and rapidly began to lose power. The pilot reported that he began the memory items for an engine failure in cruise flight starting with moving the fuel selectors to the inboard tanks. The airplane immediately began to lose altitude, and shortly after, they had descended below the tree level. The pilot took control of the airplane and turned to a field just ahead of them. The airplane stalled just above the ground, and the right wing contacted the ground first. The pilot stated both side windows shattered during impact; and within 2 seconds, the right outboard fuel tank exploded; and a postimpact fire ensued. Both pilots egressed through the rear door.

The copilot stated he was training in the airplane and did not have a multiengine rating. He stated he did not have any official hours flying the airplane with an instructor but had flown the airplane for about 200 hours. His description of the accident flight was consistent with that provided by the pilot. He further stated that when he turned over control of the airplane to the pilot during the last few seconds of flight, he looked at the fuel tank quantity gauges, and they were both reading “zero.”

Postaccident examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that the airplane impacted the ground with the right wing first and slid sideways through the field. Both engines were fractured off, and neither engine exhibited evidence of power at the time of impact. The fuselage and right wing were consumed by fire. The left wing was still attached to the fuselage. The left outboard fuel tank was completely full of fuel, and the inboard tank was empty.

Further examination of the airplane revealed that the crossfeed valve was found in the “crossfeed/open” position. No fuel was observed in the valve or attached fuel lines during disassembly. A functional field test was performed on the valve with low pressure air, with no anomalies were noted. The left fuel selector valve was found in the “OFF” position, and the control cables were secured. No fuel was observed within the fuel line between the valve and gascolator. The right fuel selector valve was thermally damaged and could not be examined or functionally tested. No other anomalies were noted in the engines or airframe that would have precluded normal operation before impact.

The fuel system consisted of four flexible fuel cells, two in each wing. The outboard fuel cells held 40 gallons each, and the inboard fuel cells held 56 gallons each. The right and left fuel systems were independent of each other and were connected only when the crossfeed system was activated. The airplane also had nacelle tanks installed, one 27-gallon capacity tank in each engine nacelle.

The fuel management controls were located in the fuel system control panel mounted between the front seats on the forward edge of the wing spar carry-through cover. Located on the fuel control panel were the fuel tank selectors, fire wall fuel shutoffs, and the crossfeed control. Two fuel gauges were mounted in the overhead switch panel. The right gauge indicated the fuel quantity in the right-wing fuel cells, and the left gauge indicated the fuel quantity in the left-wing fuel cells. The gauges were connected electrically to the fuel selector and indicated the fuel quantity of the cell selected.

The PA-31-325 Pilot’s Operating Manual (POM) states the following:

During normal operation of the fuel system, each engine is supplied with fuel from its respective fuel supply. Selection of the controls on the right side of the control panel provides fuel from the right inboard or outboard fuel cells to the right engine and left fuel control selection provides fuel from the left inboard or outboard fuel cells to the left engine.

For emergencies, fuel from one system can supply the opposite engine through the use of the crossfeed system. The crossfeed valve is located at the inboard rib assembly of the left wing butt area and is intended for emergency use only, (See Airplane Flight Manual). The crossfeed is controlled by a knob in the center of the fuel control panel, and under all normal conditions should be in the off position.

NOTE - The crossfeed system is not intended for normal operation. When the crossfeed valve is on, be certain the fuel selector valve on the tank not in use is off, and the procedures outlined in the Airplane Flight Manual are followed.

The accident fight was about 3.5 hours in duration. According to the POM, the estimated fuel burn at normal (245 brake horsepower) power was 33.1 gal/hr.