The reward for flying something you’ve built cannot be encapsulated in words. It’s not for everybody.
Only a small percentage of pilots would think to consign their fate to their own handiwork. That’s because the builder must be ever mindful during the construction.
Statistics from the Experimental Aircraft Association show that of the approximately 211,000 U.S.-based general aviation aircraft, about 33,000 are listed as experimental. Most of those are homebuilt. About a dozen of these experimental aircraft exchange hands annually.
I found more than 600 reports submitted by pilots of experimental aircraft in NASA’s Aviation Safety Reporting System database. The most intriguing were from those who had recently purchased one and encountered problems normally avoided in factory-manufactured, FAA-certified aircraft.
For instance, a pilot bought a GP-4 experimental airplane. He was its third owner. He filed a NASA report after suffering a loss of power over his home field. He declared an emergency and landed successfully.
This particular aircraft had fuel gauges and a fuel flow/totalizer instrument. According to the pilot, the gauges were not accurate. During the incident flight, his gauges indicated his fuel tanks were empty even though the totalizer reported 13.3 gallons remaining at the time the engine lost power. Because of those indications, he admitted to ignoring what the gauges were telling him.
After the incident, he sumped both tanks and found them empty. When he added 3.5 gallons to the right tank, the engine started.
“In my honest opinion,” he wrote, “the discrepancy between the heretofore reliable fuel totalizer and the actual gauges led me to disregard the gauges, the wrong response.”
This pilot also noted that the arrangement of the fuel tanks prevented him from physically checking the tanks during the preflight inspection.
He concluded his report with three corrective actions.
First, he vowed to replace the gauges with a more modern system. Second, he vowed to recalibrate the fuel flow/totalizer instrument over several flights to test against real-world results. Third, he vowed never to fly without full tanks and to set a never-exceed flight time of 4.5 hours until the first and second corrective actions were satisfied.
Another pilot bought an airworthy, kit-built plane secondhand. During a flight to collect “a single performance data point” over his home airport, he experienced engine failure. He landed successfully.
Before the flight, he added 20 gallons to the tanks for a total of 25.
“I had about five gallons of fuel remaining,” he wrote in his report. “It’s possible that my original measurements of unusable fuel were inaccurate for some combination of the flight conditions.”
It’s also possible his fuel computer had bad data.
At the time he submitted his NASA report, he still hadn’t solved the problem. In fact, he wrote of the incident, “The engine ran normally for the taxi back to the hangar.”
All homebuilt and kit-built experimentals come with plans, with the goal of making the building process easier, as well as creating some sort of standardization across the fleet.
The latter goal is not one that always translates from the paper to the plane because decisions on gauge types are often left to the builder. Builders have many reasons why they will choose a certain gauge, and what may work for the original builder-owner may not work for subsequent owners.
Additionally, builders may install fuel systems in a non-standard layout. Couple that with missing or incomplete documentation and you have the recipe for a very interesting flight.
Such was the case for a pilot and his pilot friend while ferrying a recently purchased Glasair. The original owner and builder had died, so the plane was being represented by the deceased builder’s pilot friend.
The buyer had an A&P mechanic with inspection authority (IA) perform a four-hour pre-purchase inspection where the Glasair was hangared. No airworthiness discrepancies were found. Both the purchasing pilot and his friend reviewed cockpit pictures and the pilot operating handbook before picking up the plane.
The seller had flown the Glasair frequently, so the buyer felt comfortable asking him about its fuel system.
“I specifically queried him about the airplane’s fuel system,” he wrote. “I noted that the fuel selector had three positions: On, Off, and Aerobatic.”
The pilot representing the airplane for his deceased friend said that selecting the On position meant drawing fuel from the main tank. The IA concurred, based on his own research and familiarity with other Glasairs he’d serviced.
The new owner and his pilot friend picked up the Glasair. They proceeded to do several run-ups along with other systems checks before filling up the two tanks. Finally, in accordance with the onboard checklists, the seller and the IA, they chose the On position for the fuel selector, did a final run-up check and departed for the Glasair’s new home.
“At 10,500′ and about 7 miles northwest and past airport ZZZ2, and 25 minutes into the flight, the engine coughed and quit cold,” wrote the pilot.
His scan of the instruments revealed no anomalies. The main fuel tank gauge indicated 3/4 full, which jibed with his calculations for time aloft. They turned on the fuel pump and switched to Aerobatic, to no avail. The pilots decided to divert to ZZZ2 because they had sufficient altitude to deadstick the airplane to it.
Just before final approach, the pilot decided to try one last ditch maneuver to restart his engine. He had been told the two pumps labeled Left Transfer Pump and Right Transfer Pump transferred fuel to the header tank from the main tank. He turned them on. The engine started, producing full power. The pair made a precautionary power on landing at the diversion airport.
In debriefing the incident, the pilots surmised they might have actually been burning fuel from the header tank despite the fact the fuel selector was in the On position, allegedly the position for the main tank.
The new owner then called the seller and asked if, in fact, the main tank was the one feeding in the On position rather than the header.
“I told him I suspected that was incorrect, but he held to his opinion,” he wrote.
The pilots returned to the Glasair three days later. They discovered three things:
- The main tank had less fuel than on departure from ZZZ2.
- The header tank was full, likely from the transfer pumps running during the emergency.
- It wasn’t possible to track all the fuel lines inside the cockpit due to the aircraft’s build.
The pilots performed two thorough assessments. The first involved the fuel system transfer pumps. They confirmed by sight and by sound that both the left and right transfer pumps were sending fuel to the header tank.
They then compared their physical inspections with the plane’s electronic management system (EMS). The EMS showed the header tank as the primary fuel tank. An engine start and 10-minute run-up confirmed this.
This is when the buyer’s pilot friend spoke up about something he’d noticed during the flight. He had seen two lights illuminate: One stated “header tank 70% full” and the other “header tank 25% full.” He told the buyer he hadn’t been concerned because they weren’t running on the header. Also because other warnings and false alarms had been generated by several signal problems unrelated to critical auxiliary EFIS and EMS functions, he had chosen to ignore all warnings.
The pair came across hand-scribbled notes from the builder that indicated a single transfer pump needed to be running to keep the header tank full and operational. Using this newly discovered information, they test flew the Glasair without incident.
“It was now obvious that the aircraft’s non-standard fuel system, where both settings for the selector drained from the single, small header tank, and the undocumented procedures required to keep it full, along with incorrect information from the seller, had caused the header fuel tank to run dry,” concluded the pilot in his report.
He noted the need for a better briefing from the seller. He also determined the need to test all not clearly documented aircraft systems in an experimental aircraft. And finally, he emphasized heeding all annunciated warnings.
Two of these three incidents highlight something Harvard psychology professor Ellen Langer calls “mindlessness.” It’s defined as an inactive state of mind where humans overly rely on past experiences to determine their reactions to present circumstances.
Mindlessness should not be an option for pilots.”
Most likely, these pilots learned to fly in factory-manufactured, FAA-certified airplanes with traditional systems and gauges. So when they took possession of their experimental aircraft, they mindlessly assumed the fuel systems would operate in the same way.
Furthermore, when each airplane clearly displayed conflicting information regarding their fuel state, the pilots mindlessly chose to believe the more hopeful gauge and ignore the warnings of the other. Langer calls that a case of where “we let the past determine the present. In such a state, we are typically in error but rarely in doubt.”
Of all states to be in, mindlessness should not be an option for pilots.