One assignee leads with 46 of the 168 records in scope, far ahead of the rest of the ranked field — fifth place holds 10 records and tenth place holds 4. This is a leader-plus-long-tail structure rather than an evenly distributed field, so a freedom-to-operate review should start with that leader's claim scope before working down the ranking. The full ranking covers 61 companies counted in records, not a top-50 or top-100 cut.

Filings dipped to 3 records in 2021 and recovered to 8 by 2024, a +167% increase over that span, which points to renewed activity rather than decline. The historical peak was 15 records in 2017. Figures for 2025 and 2026 look lower only because publication typically lags filing by about 18 months, so those years are still filling in and should not be read as a genuine slowdown.

The large majority of records, 81.0% of the 168 in scope, sit under IPC class B64C for aeroplanes and helicopters, confirming this is primarily an airframe mechanism topic. A smaller but consistent cluster falls under F03D for wind turbines (10.1%) and F16C for shafts, bearings and couplings (8.3%), pointing to component and application overlap between aircraft flap hardware and wind blade flap systems. Smaller shares touch aircraft equipment, jet propulsion, digital processing and surface treatment classes.

US20250313329A1, filed by Sherpa Aircraft Group Inc. and published 2025-10-09, describes an extreme short take-off and landing airplane with Fowler flaps mounted on external flap tracks that extend aft of the trailing edge, enabling both rotation and translation of the flap, alongside flap coves and Frise-type elements. Its claims are specific to that combined geometry rather than to Fowler flaps or flap tracks generally, so the blocking effect is narrower than the abstract might suggest. Anyone designing a similar STOL wing should check the exact track geometry and kinematic claim language rather than assume Fowler-flap-plus-track designs are broadly blocked.

The clearest gaps sit in branches that appear only thinly across the 168 records: flap skew sensing integrated with digital monitoring, flap gap control tuned for cruise rather than takeoff and landing, and wind-blade-specific flap track bearing designs. These areas show enough activity to confirm the problem is recognised, but not enough dense filing to suggest the claim space is occupied. A first claim there would likely combine a specific sensing or control method with a named flap geometry rather than claim the mechanism broadly.