The FAA has issued an AD requiring inspection of the stabilator control system of all Piper Cherokees, Lance/Saratogas, Senecas and Seminoles that are 15 years old and older. The FAA estimates that the AD applies to about 34,000 airplanes in the U.S.
What is troubling to me about this AD is that it requires an inspection that is already required by the normal maintenance rules. It looks to me like the FAA has acknowledged that many airplanes—perhaps 34,000—are not being inspected properly so a new, double requirement, is now in place.
As I’m sure you know, airworthiness directives are issued to correct an unsafe condition in a certified aircraft, including all of its important components such as engines and accessories. The AD system is in place because unexpected defects in a design, or errors in manufacturing, can occur. Often an AD addresses unexpected cracks or other failures in airframe structures. Or an AD can be issued to locate and remove components that mistakenly entered service with a defect in materials or construction.
But this new AD on a huge chunk of the Piper fleet has nothing to do with unexpected or surprising issues with the pitch control system. This AD requires a visual inspection of the entire control system from the control column all the way to the stabilator including cables, pulleys, brackets and fittings. The inspector is required to look for corrosion, cracks or wear. Duh.
Having just bailed my airplane out of its annual inspection with a surprising $6,000 tacked onto the normal bill to pay for repair of a crack in one elevator skin I have to believe all that time and money was spent on carefully inspecting everything. Wasn’t the shop and its authorized inspector required to look for corrosion, cracks and wear on all parts of the airframe? Isn’t the pitch control system pretty important and something that should be looked at closely while all those inspection hatches and interior components are removed? The answer is yes.
In fairness, the AD on the Pipers requires that the control cable turnbuckles be unscrewed for a complete look at the components, and that wouldn’t be a typical inspection procedure. But if a careful inspector saw the beginnings of suspected corrosion or fraying of the cable on or near a turnbuckle he would certainly take it apart for a closer look in any case.
There have been two accidents and one incident involving failure of the pitch control system in Pipers covered by the AD. The NTSB has been pressuring the FAA to do something to prevent additional accidents. Fine. That’s the NTSB’s job. But does a new rule—the AD—force inspectors to do what they were already required to do?
Light piston airplanes such as the Pipers covered by this AD are certified under the concept that regular inspections will find and fix problems before they threaten the integrity of the airplane. So, it was determined during certification that there is enough margin in the Piper’s pitch control system that small cracks, the beginning of corrosion, or wear will be found during annual or 100 hour inspections and repaired before leading to actual failure. Regular inspection is the foundation of certification.
Larger airplanes are certified under fail safe and damage tolerance concepts. That means in a transport airplane the wing spar, for example, must have multiple elements that can carry the design loads if one of the elements cracks through or in some other way fails. Inspections are still important for transport airplanes, but there are structural backups in case something breaks between inspections.
The FAA goes even further for transport airplanes and all twin turbine airplanes by requiring an approved maintenance plan. Those approved procedures demand very specific inspections including required overhaul or replacement times for critical components.
So far the inspect and repair concept has worked well for the piston fleet. In my case, the crack in the elevator skin was about six inches long and it was impossible to know how long the crack had been there. But the crack was discovered, as it should have been, during a normal inspection, it was fixed, and airworthiness was not threatened.
The new AD on the Pipers looks like a first step toward applying the required approved maintenance procedures for turbines to piston airplanes. Now inspectors will have to not only examine the pitch control system, as they have been required to all along, but they will also need to record in the permanent airplane records that the inspection was performed. If nothing else, just the paperwork of researching the AD and recording that it has been complied with adds to the cost of what should be normal maintenance.
With this AD the FAA has signaled that is has lost confidence in the normal required inspection system for light airplanes, or that it is taking early steps to develop required maintenance procedures for all airplanes. Either way, it’s not a good situation. By the FAA’s estimate owners of the Piper fleet affected will spend more than $14 million to comply. And airplane owners who had been paying for complete and valid inspections as already required will share in the bill along with those who cut corners on maintenance. Actually, the corner cutters will probably ignore the AD just as they have skipped over other inspection requirements so only the careful airplane owner foots the bill.