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The FAA is out with a new airworthiness directive for Textron Aviation's B300 and B300C (the King Air 350 and 350C) which tightens how often operators must inspect the wing spar and wing-to-fuselage attach structure for cracks. The AD (2026-15-05) takes effect August 10, 2026, with comments running through September 8.Textron's own manual had the wrong numbersTextron caught the problem itself. Its Airworthiness Limitations Manual carried the wrong wing-inspection intervals for airplanes operating at 16,500 pounds max takeoff weight, the heavy version of the 350. Textron's revised structural inspection and repair manual (SIRM) now sets separate intervals for 15,000-lb and 16,500-lb airplanes, guided by hours flown.With a 25 hour or 30-day compliance clock ticking (for certain models), the FAA skipped public comment before adopting it, using the good-cause exception to the APA. A normal comment round would have left some airframes overdue before the rule could take hold. The compliance clock, by airframe hoursThe AD hits heavy-weight B300/B300C airplanes running one of three kits (130-4402, 130-4030, or 130-4014, depending on serial number). It skips airplanes that Textron Special Missions already evaluated and covered with serial-number-specific ALM/SIRM supplements. Compliance timing runs off time-in-service:Less than 3,800 hours - before reaching 3,800 hours of time-in-service, or 25 hours/30 days from the effective date, whichever occurs later.Between 3,801 and 7,400 hours - within 200 hours or 6 months, whichever is earlier.More than 7,401 hours - within 25 hours or 30 days, whichever occurs first.The new intervals cover the wing-to-fuselage attach angles and the outboard wing, and they range from 2,500 to 29,200 hours depending on serial number and kit. On later-serial airplanes, the wing center section and outboard structure carry no life limit, as long as inspections and replacements stay on the SIRM and maintenance-manual schedule.In a low-ball figure from the FAA, the cost comes to one hour of work, $85 per airplane, which is really just a paperwork amendment. The real figure will work out to around $9,605, which covers revising the documentation and the inspection work itself.Why a paperwork AD still hits resaleThe 350 is one of the hardest-working owner-flown and Part 135 turboprops around, and this is a structural AD based on an unsafe condition, not a paper exercise. For sellers, it's a prebuy checklist item: the buyer needs to know which kit was installed, which serial-number range the airplane falls in, and whether its total time already exceeds the new interval. For Part 135 operators flying heavy 350s on the edge, the phased schedule hits high-time airframes hardest, and 25 hours or 30 days gives little leeway. Anyone looking at a 350 today needs to know about the ALM revision first and foremost.Browse current King Air 350 listings on GlobalAir.com