When the wing of an airplane separates in flight, it gets people’s attention. So last year, when the left wing of a Piper Arrow came off of an Embry-Riddle Aeronautical University training plane, it was big news, not only because it’s a horrifying scenario over which the pilots had no control, but also because everyone wanted answers. The 30-page final report by the National Transportation Safety Board (NTSB) not only goes into the minutiae of how it happened but asks bigger questions about how we think of training and training aircraft.
On April 4, 2018, two were killed in a crash of a Piper Arrow retractable-gear single-engine trainer that happened during a commercial certificate FAA checkride in Daytona Beach, Florida. The immediate cause of the crash was obvious from the start. The left wing of the Arrow separated in flight, causing the Arrow to immediately go out of control and crash. The failure was catastrophic and unrecoverable. The two who died in the crash were the commercial pilot applicant, Zach Capra, 25, a private pilot at the time of the crash, and the pilot examiner, John Azma, 61, who was an ATP.
The Board released an update on the investigation a couple of weeks after the crash. In the release, it shared photographs of the wing structure that had failed due to fatigue cracking. The plane, a 2007 PA28R Piper Arrow, had a lot of time on it for an 11 year old plane, 7,662 hours, but that is not uncommon in a training environment. The plane had gotten an inspection about 30 flight hours before the accident flight.
You can read the report here.
I won’t go into the metallurgical, aerodynamic or physics data in detail that the NTSB gets into, but in short, the report asks this question: Do airplanes utilized in the training environment get subjected to more abuse than those used for personal flying?
The answer they arrived at, in conjunction with Piper, is yes. Why that’s so is a complex calculus, one that’s open to differing approaches and interpretations, but in short, the conclusion is that trainers get more and stronger loads than their non-trainer counterparts. To most pilots, that never seemed like a big deal. We know that planes are built with plenty of margin over the certificated load factors for every component and system. So if a plane gets landed, a maneuver well within the plane’s capability, thank goodness, what does it matter if it gets landed 100 times instead of seven times?
arrows indicate fatigue origin areas and dashed lines indicate approximate fatigue boundaries
The conclusion the NTSB reached, and this is a big deal, is that it matters a lot, over time that is. Here’s the Board’s statement of probable cause:
The National Transportation Safety Board determines the probable cause(s) of this accident to be: 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.
What precisely the FAA will choose to do with this information remains to be seen, but it’s likely that more and more involved inspections on training aircraft, especially their wing spars, will be mandated at some point.
But more than that, it’s likely that from now on everyone will be looking more closely at the differences between the punishment personal use planes get compared to trainers, and how we address those differences in terms of design, manufacture, maintenance and operations going forward. That is a lot.
