There's not enough data, nothing to show that there's a problem, so there's no reason to issue an airworthiness directive (AD). That's what AOPA told the FAA about its proposal to issue a new AD concerning spar corrosion on Twin Beech 18s.
"Given that the current AD appears to have effectively removed the unsafe condition, the FAA should provide the supporting data to show an unsafe condition that would now justify lowering that inspection interval to 1,000 hours or 48 months," said Luis Gutierrez, AOPA director of regulatory and certification policy.
The FAA recently circulated an "Airworthiness Concern Sheet" proposing to supersede an existing AD with one that would reduce wing spar inspection periods from 1,500 to 1,000 hours, or 48 months, whichever comes first.
AOPA contacted the Twin Beech 18 Society, which reported that it was unaware of any information that would justify the change.
AOPA noted that the current AD requires a wing strap installation and repetitive inspections, which has effectively addressed the problem of spar cracks and corrosion. "In fact, the [current] AD requirements have worked so well that not one Beech 18 airplane has been lost because of wing failure," AOPA said.
The association also told the FAA that if there were a problem, the agency should certainly have the data, since the current AD requires a report to the agency of any cracks or corrosion discovered during the required inspections.
AOPA also said that the wing straps installed under the current AD provided a redundant load path in the event of failure of the existing structure. The FAA had overstated the risk by not recognizing that additional safety feature.
The association did recommend that the FAA issue a special airworthiness information bulletin (SAIB) to highlight the areas of concern and request that Twin Beech owners report any corrosion found during annual inspections or inspections conducted under the current AD.
October 3, 2005