While the National Transportation Safety Board does not normally determine a probable cause for an aircraft accident for months, or sometimes years after an event, the preliminary report the Board released of a July 11, 2019, accident involving an Icon A5 made it clear the pilot did not understand how to calculate the airplane’s actual fuel consumption in a variety of conditions. The Icon’s 100-hp Rotax 912iS engine quit as the airplane approached a 3-mile left base leg for Runway 16 at Chicago Executive Airport (PWK) just prior to darkness. Investigators found the Icon’s fuel tank to absolutely dry. The pilot escaped unharmed, but the A5 was destroyed when the aircraft struck trees and terrain in a nearby forest preserve.
The 74-year old pilot and his wife own identical Icons and both departed Indianapolis Eagle Creek Airpark (EYE) with 17 gallons of fuel in each airplane. A full tank would have required 20 gallons of fuel. Perhaps the pilot and his wife were concerned about departing EYE heavier than the aircraft’s maximum takeoff weight, although that is unclear. The pilot reported his flight planning software calculated 13 gallons of fuel would be required for the estimated 2.4-hour flight from EYE to PWK and a distance of 165 nm. The pilot expected both aircraft to land with roughly an hour’s reserve, approximately four gallons of fuel.
The NTSB tried to determine if the pilot miscalculating the fuel burn, the distance or possibly the wind, or even an engine problem might have been responsible for the accident. Aiding the investigation was a digital data module that recorded basic GPS, engine and flight parameters. A preliminary review of the available data indicated the flight lasted 2.3 hours at a cruise altitude of about 3,000 ft msl with an engine manifold pressure of 26.5 to 27 inches of mercury. The engine data also indicated that 60.4% of the flight, about 1.4 hours, was operated in excess of 5,500 rpm. The Rotax 912iS rpm redlines at 5,800 rpm and carries a placard against operating the engine at that power setting for more than five minutes at a time.
The data module determined the pilot ran the Rotax at nearly maximum power for more than half the flight. For 1.2 hours of flight, the pilot operated the Rotax at 100 percent power in violation of the aircraft’s placard. In addition to violating the pilot’s operating handbook, the pilot failed to realize how much extra fuel the engine would consume at such high power settings, considerably more than what he’d planned for. His flight planning software based the trip on a 4.8 gph economy power setting. The manner in which the pilot operated the Icon however, caused the Rotax to burn between 6.9 and 7.1 gph. That meant it would have been impossible for the aircraft to land in Chicago with the expected fuel reserve.
The NTSB said, “A post-accident examination of the airplane revealed the fuel tank did not contain any useable fuel and that the low fuel annunciator light was illuminated [at the time of the crash].” The pilot noted his wife was able to safely fly her A5 to PWK although she landed with just 1.4 gallons of fuel (1.2 gallons usable) remaining after her 2.4-hour flight.