Report cites metal fatigue in 2018 Piper Arrow crash

The NTSB on Sept. 3 issued the much-awaited report on the accident involving a designated pilot examiner and a private pilot taking a commercial pilot practical test in a Piper Arrow registered to and operated by Embry-Riddle Aeronautical University. The airplane, manufactured in 2007, was climbing after a touch-and-go landing when “the airplane's left wing separated near the wing root and the airplane collided with terrain,” the report said. It added that previously established inspection criteria “were insufficient” to detect the developing structural flaw.

Repercussions from the accident included the FAA in December 2018 proposing an airworthiness directive that would require inspecting a wide range of Piper PA–28 models that have reached significant hours in service for metal fatigue of main wing spars.

Earlier this year, AOPA urged the FAA to delay implementing the AD until after the NTSB issued its final accident report, and after more information was collected about the PA–28 fleet, allowing the FAA to appropriately narrow the scope of any regulatory action.  AOPA’s position was echoed by the NTSB, which expressed concern to the FAA about the risks of ordering invasive inspections of numerous older aircraft.

“We have been following this issue closely and have been in contact with the FAA and others on potential next steps,” said AOPA Senior Director of Regulatory Affairs David Oord.

The complete NTSB statement of the probable cause of the accident noted “extensive fatigue cracking in the left-wing main spar lower cap and doublers, which resulted in the in-flight separation of the left wing. The fatigue cracks initiated and grew to a critical size due to flight and ground loads associated with flight-training involving flight-training maneuvers, significant operation at low altitudes and frequent landing cycles. Previously established inspection criteria were insufficient to detect the fatigue crack before it grew to a critical size.”

The designated pilot examiner conducting the checkride—which took place in mild weather with no reported turbulence—was described as a 61-year-old pilot with 27,600 hours total time. The applicant, 25, was an instrument-rated private pilot with 218 hours including 26 hours in the accident make and model, the report said.

Citing university maintenance records, the NTSB noted that the accident airplane’s airframe “had accumulated 7,690.6 hours of operation before the accident flight, and 28.3 hours since its most recent annual inspection, which was completed on March 21, 2018. Before the accident flight, the total landing cycles were 33,276,” according to the records.

The 30-page report referred to two previous wing-separation events in PA–28-series aircraft and discussed urgent NTSB safety recommendations that had been issued, and the FAA’s responses including previous ADs. It summarized interviews with university flight instructors who said the PA–28R-201 was used “for complex operations only and accounted for about one-third of the commercial flight training.”

As for possible causes of structural stresses on airframes, “When questioned about emergency descents, all the instructors stated that the maximum G-load was no higher than perceived 1.5 Gs, with the objective to descend the airplane as rapidly as possible while maintaining operational limitations,” it said.

However, the NTSB observed that the “low-altitude flight training and frequent landing environment likely resulted in the accident airplane accumulating damaging stress cycles at a faster rate than a personal use airplane.”

Examining other possible reasons why airframes might experience structural impairment, the report broached the potential impact of severe weather, but noted that prior to Hurricane Matthew striking the area in 2016 and Hurricane Irma’s arrival in 2017, flyable Embry-Riddle aircraft were relocated to safe havens at airports in Alabama in accordance with the university’s emergency response plan.