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Open for Comment: Airworthiness Directives; Columbia Helicopters, Inc. and Restricted Category Model CH-47D Helicopters

Transportation Department — The FAA proposes to adopt a new airworthiness directive (AD) for all Columbia Helicopters, Inc. Model 234 helicopters and all Restricted Category Model CH-47D helicopters. This proposed AD was prompted by reports of corrosion detected on certain flight control rigid connecting links (connecting link). This proposed AD would require repetitive borescope inspections of the connecting links for corrosion and, depending on the results of the inspection, repair of the corrosion or replacement of the connecting link with a serviceable part. This proposed AD would also require reporting the results of these inspections and would prohibit installing a certain part-numbered connecting link or a connecting link with an unknown part number on a helicopter unless certain requirements are met. The FAA is proposing this AD to address the unsafe condition on these products. (44 days remaining)

The Book of Numbers

Open for Comment: Airworthiness Directives; Various Helicopters

Transportation Department — The FAA proposes to supersede Airworthiness Directive (AD) 2015-20-12, which applies to certain Sikorsky Aircraft Corporation Model S-61A, D, E, L, N, NM serial number (S/N) 61454, R, and V; Croman Corporation Model SH-3H; Carson Helicopters, Inc., Model S-61L and SH- 3H; Glacier Helicopter, Inc., Model CH-3E; Robinson Air Crane, Inc., Model CH-3E, CH-3C, HH-3C and HH-3E; and Siller Helicopters Model CH-3E and SH-3A helicopters. AD 2015-20-12 requires calculating or recalculating the hours time-in-service (TIS) of the main rotor shaft (MRS), determining whether the MRS is repetitive external lift (REL) or non-REL, performing a nondestructive inspection (NDI) for cracks, replacing any MRS that has cracks, replacing parts before their life limits and removing from service any parts that have exceeded their life limits. This proposed AD would also require establishing retirement lives for each REL MRS, including reducing life limits and allowing for modification of life limits based on service information, and removing any MRS with oversized dowel pin bores. Since the FAA issued AD 2015-20-12, a design re-evaluation shows that the MRS on certain helicopter models requires a lower life limit. This proposed AD would retain some of the requirements of AD 2015-20-12, and would also lower the retirement life for a certain MRS installed on certain helicopters and would update the type certificate holder name for some of the affected helicopter models. The FAA is proposing this AD to address the unsafe condition on these products. (44 days remaining)

The end of NIPs

Paper 176 v0.1 — Fermat Numbers F_5–F_11: Empirical v_2(ω_{F_n}(3)) Measurement + Lean 4 Axiom-Free F_9 Excess Witness (Rei-AIOS)

Paper 176 v0.1 reports the empirical measurement of v2(ω{Fn}(3)) — the 2-adic valuation of the multiplicative order of 3 modulo the Fermat number Fn = 2^(2^n) + 1 — for n = 5, 6, 7, 8, 9, 10, 11, and provides the Lean 4 axiom-free structural evidence that F9 exhibits an excess...

Open for Comment: Hazardous Waste Management System; Identification and Listing of Hazardous Waste; Correction

Environmental Protection Agency — On March 26, 2026, the Environmental Protection Agency (EPA) published a Federal Register document proposing to grant an exclusion from the list of hazardous waste to WRB Refining LP located in Borger, Texas. The proposed rule had an incorrect docket number. This action informs the public of the correct docket number. The EPA is also extending the comment period for the proposed rule by 22 days to May 20, 2026. (27 days remaining)