DAYTONA BEACH — An initial investigation into a plane crash that killed an Embry-Riddle Aeronautical University student and his flight instructor has found that the left wing, which separated from the plane mid-air, had fatigue cracks, according to a federal report.
In the National Transportation Safety Board preliminary report released Tuesday, investigators provided more details into the April 4 crash that killed ERAU student Zach Capra and Federal Aviation Administration pilot examiner John S. Azma.
The report said that an examination of the plane's left wing found fatigue cracks on the wing spar — a metal structure that bears the load of the wing. According to the report, the left wing separated from the "fuselage near the wing root" and the fatigue began "at or near an attachment bolt hole."
Mike Busch, a maintenance expert who is often called upon in aircraft litigation, explained that the findings show that the fractures were at the point in which the wing attaches to the cabin.
According to the report, an examination of the left wing's main spar “revealed that more than 80 percent of the lower spar cap" exhibited fracture features "consistent with metal fatigue." Busch said that upper and lower caps are largely what gives the wing spar its strength.
"When the airplane is experiencing positive g-force, then the primary stress is on the lower spar cap," he said.
Similar cracks were also found in the plane's right wing at the same point where it attaches to the fuselage, according to the report. The report said that "none of the surfaces exhibited corrosion or other preexisting damage."
ERAU spokesman James Roddey said that the university "will let the report stand on its own" and "will have no other comment at this time."
The single-engine plane — a Piper PA-28R-201 aircraft, better known as an Arrow — was manufactured in 2007 and had accumulated 7,690 hours of flight time. It had received its annual inspection on March 21, just two weeks before the crash, and had flown some 28 hours since then, the report said.
Roddey said that all of the university's Piper Arrows continue to remain grounded as the investigation continues.
A typical yearly inspection of a Piper PA-28 wouldn't necessarily reveal fatigue cracks, which develop over time from repeated stress, Busch said.
"It depends on where the fatigue cracks were," said Busch, who said he was not an expert on the maintenance of that particular plane. "Fatigue in the spar caps might or might not be picked up in an annual inspection."
He described the plane's several thousand hours of flight time in just over a decade as "heavy usage." Most of these planes are privately owned, he said, and don't fly nearly as much.
At the time of the crash, Capra, a 25-year-old Navy veteran, was taking his commercial pilot license test with Azma, an experienced pilot examiner and father of four sons. According to the report, the plane had performed a "touch-and-go landing" and then taken off again, reaching an altitude of 900 feet and flying at a speed of 92 mph before "radar contact was lost."
Crash witnesses, who included air traffic controllers, said the plane was flying normally when "the left wing separated from the fuselage," causing it to spin out of control and then slam into a cow pasture along Tomoka Farms Road near the Daytona Flea & Farmers Market.
Busch said that the maneuvers that the pair were performing shouldn't have overly stressed the plane's wing. But other information in the report indicated that the wing might have been stressed prior to the crash.
"This is very unusual," Busch said. "These aircraft don't really have a history of wing spar fatigue problems."
He recalled only one other instance of a wing separating from a Piper PA-28. That crash in 1987 caused the NTSB to issue an emergency order, requiring all of those model planes with more than 5,000 hours of flight time to have their wings removed and inspected.
Busch said that the ERAU crash has likely caught the attention of federal aviation officials and could result in another mandatory inspection.
"Clearly, the finding for this crash is going to mean that high-time PA-28 airplanes will need to be getting more thorough inspections of the particular area where the cracking was found," he said. "The FAA is going to be looking into it and will come up with an appropriate inspection feature to detect the condition before it becomes safety critical."