Investigators looked into the pilot's performance and certification along with flight planning. An autopsy was performed on the pilot by the Lake County Coroner's Office. The study listed multiple traumatic injuries as the cause of death. The FAA Civil Aerospace Medical Institute prepared a Final Forensic Toxicology Accident Report on toxicological samples taken during the autopsy. The report, in part, stated that traces of marijuana were detected in his tissues. A pre-employment drug test on April 14, 2011, reported negative indications of drug use.

The pilot-passenger told Safety Board investigators “the pilot acted abnormally sporadic and weird in Florida,” but the investigator's report does not elaborate.

The pilot held a first-class medical certificate, dated Feb. 15, 2011, with limitations for hearing amplification and corrective lenses. The pilot previously reported to the FAA that he had a history of convictions for driving under the influence on both May 31, 2002, and Feb. 1, 1997.

The operator initiated a background check in accordance with the Pilot Records Improvement Act of 1996 (PRIA) on the pilot. This check showed his training records and check rides at previous employers and also revealed no legal enforcement actions resulting in a finding of a violation pertaining to the pilot. It listed a possible match and gave contact information for a Department of Transportation Compliance and Restoration Section in reference to checking the pilot's driver's record. The operator did not get that background check but was aware of the pilot's history of convictions.

The passenger-pilot said that the senior pilot had done all the flight planning for the trip. Investigators could not locate the original flight planning records but were able to re-create the navigation logs in consultation with — the resource used by the pilot for his planning.

The accident flight plan showed a proposed departure time from JES of 1708, a proposed cruising altitude of 10,000 ft. MSL en route to PWK, 5 hr. of fuel on board, and it listed DuPage Airport as an alternate airport.

The flight plan logs showed that the 182 gal. of usable fuel available for the Piper Chieftain should have been sufficient for all flight legs that day. The final accident leg from JES to PWK would have required the most fuel. calculations assumed a fuel burn rate between 34-37 gph for cruise and the operating manual indicated a fuel burn between 26-35 gph (depending on the power setting) with the engines leaned to best economy. The average actual fuel burn computed for the flight legs flown on Nov. 28, 2011, was 47 gph.

Fuel records recovered from the wreckage indicated that the airplane was filled to its capacity with fuel at CFJ, PXE and at JES. The fuel records also indicated that only 75 gal. of fuel were added at PBI. A nominal fuel burn rate of 30 gph would indicate that landing with a minimum of 22.5 gal. of fuel would meet the 45-min. IFR fuel reserve requirement: With the Chieftain's 182 gal. of usable fuel, the maximum amount of fuel that should be added after a flight conducted under instrument flight rules is 159.5 gal. N59773 was serviced with 167.3 gal. and 165.0 gal. at PXE and JES, respectively.

The fuel system consisted of fuel cell, engine-driven and emergency fuel pumps, fuel boost pumps, control valves, fuel filters, fuel-pressure and fuel-flow gauges, fuel drains and non-icing fuel tank vents. Fuel could be stored in four flexible fuel cells, two in each wing. The outboard cells hold 40 gal. each and the inboard cells hold 56 gal. each, giving a total of 192 gal., of which 182 gal. were usable.

The fuel management controls were located in the fuel control panel at the base of the pedestal. Located here were the fuel tank selectors, fuel shutoffs and crossfeed controls. During normal operation, each engine was supplied with fuel from its own respective fuel system. The fuel controls on the right controlled the fuel from the right cells to the right engine and the controls on the left controlled the fuel from the left fuel cells to the left engine. For emergencies, fuel from one system can supply the opposite engine through a crossfeed system. The crossfeed valve was intended only for emergencies. The crossfeed control was located in the center of the fuel control panel. A warning light, located on the fuel control panel, was incorporated in the firewall fuel shutoff system to indicate that one or both of the shutoff valves were not fully open.

Right and left fuel-flow warnings lights, mounted at the base of the windshield divider post, illuminated to warn the pilot of an impending fuel-flow interruption. A sensing probe mounted near each inboard fuel tank outlet activated the lights. In the event the fuel level near the tank outlet dropped to a point where a fuel-flow interruption and power loss could occur, the sensing probe would illuminate its corresponding warning light. The warning light would be on for a minimum of 10 sec. and would remain on if the condition were not corrected.