Passenger doors on Diamond DA 40s have repeatedly unlatched and separated in flight. In some cases, Diamond says, “operators forgot to latch the passenger door before flight,” and occupants tried to secure it in the air. For the rest, Diamond “was unable to find a definitive root cause.” FAA AD 2026-22-06 now mandates a flight manual revision, a detailed door inspection, and new warning placards across the U.S. DA 40, DA 40 F, and DA 40 NG fleets.

The Story: The four-seat composite DA 40 Diamond Star, built in Austria and Canada since 2000, is a modern flight-training staple, with 2,200 delivered by the end of 2020.

The issue isn’t new. Following 2010 and 2011 ADs requiring improved retaining brackets on DA 40 and DA 42 airframes, reports continued. In an October 2024 Airworthiness Concern Sheet, the FAA noted “at least 20 reports of passenger door separations from the aircraft while in flight and over 30 reports of aborted flights” across both fleets. That August, Diamond had published a service information letter describing the red safety hook as a safeguard if the door unintentionally unlatched in flight. Transport Canada mandated action via AD CF-2025-30 in July 2025, noting that the root cause of some occurrences had not been identified.

NASA ASRS reports illustrate the practical hazard. In November 2025, a DA 40 instructor noticed the door warning light at about 600 feet and reached back to close the rear door; “it unlatched and within seconds, flew/ripped clean off.” In a 2022 report, a crew left a cracked-open door alone, as the checklist advises, but it still came off as they circled back to land.

Rejecting commenters’ requests to exempt newer airplanes equipped with a secondary safety latch, the FAA said the red safety hook “was not designed to hold the door closed during takeoff,” and that the DA 40 NG has also experienced separations. Effective December 7, 2026, AD 2026-22-06 mandates Diamond MSB 40-103/MSB F4-042/MSB D4-114/MSB 40NG-084 Rev 2, published as one document, as an interim action while Diamond’s investigation continues.

Field Notes:

• Applicability & Compliance: Covers 987 U.S.-registered DA 40, DA 40 F, and DA 40 NG airplanes (the diesel DA 40 D holds no FAA type certificate). AFM revisions and initial inspections must be accomplished within 100 hours time-in-service (TIS) or 100 days, whichever comes first.
• AFM Revision: An owner/operator holding at least a private pilot certificate may insert TR-MAM-40-1203 (DA 40/F) or TR-MAM-40-1203/a (NG). Changes include a functional preflight check (pulling the outer handle while unlatched to verify the safety hook catches), a passenger briefing that closing the door doesn’t latch it, and an unconditional rule: “Do not try to latch the passenger door in flight.” Instead, slow below 140 KIAS and land.
• Inspection: Maintenance personnel must complete Diamond Work Instruction Rev 2, Section III. Airplanes under 100 hours TIS require inspection of the hook, handle operating forces, latch bolts, guide blocks, and placards. Airplanes with 100+ hours TIS add checks of the warning light, hinges, springs, retaining block, push button, door frame, and a 15 kg pull test on the hook.
• Gas Springs: For most airframes this is a one-time AD. However, if handle force at step 20(f) is under 1.8 kg (18 N) while step 20(c) unlatching force remains within 2–6 kg (20–60 N), the step 20(c) check must repeat every 100 hours until the gas spring is replaced (mandatory within 12 months after the effective date). If step 20(c) is out of range too, replacement is required before further flight.
• Findings & Costs: Deficiencies require correction before further flight; where the Work Instruction says to contact Diamond, use FAA-, Transport Canada-, or Diamond DOA-approved instructions. Credit is granted for prior compliance with Rev 0 or Rev 1, with no execution report required. The FAA estimates $331 for the initial inspection, plus $659 for a gas spring and $824 for a hook assembly, if needed. Later revisions of the MSB won’t count automatically; using one requires an AMOC unless the FAA revises the AD.

Why It Matter: On the ramp, the red safety hook looks and feels like a reliable secondary latch. In reality, it was not designed to hold the door closed on takeoff, and reaching for the handle in flight can make it let go.

Diamond’s 2024 service letter also flags a human factors trap: using the canopy’s cooling-gap position sets off the DOOR OPEN warning and “can reduce the alertness to the DOOR OPEN warning.” If it stays on after the canopy is closed, “the aural warning will not sound again,” so an unlatched passenger door can go unnoticed. And a door that leaves the airplane is a hazard below it, too: the FAA lists “injury to persons on the ground” as part of the unsafe condition. With some separations still unexplained, this interim AD may not be the last word.

Sources: FAA AD 2026-22-06, Docket FAA-2026-4633 (91 FR 68873, November 2, 2026); FAA NPRM, Docket FAA-2026-4633 (91 FR 26952, May 13, 2026); Diamond MSB 40-103/MSB F4-042/MSB D4-114/MSB 40NG-084 Rev 2, published as one document, with its Work Instruction (June 5, 2025); Diamond AFM Temporary Revisions TR-MAM-40-1203 (DA 40) and TR-MAM-40-1203/a (DA 40 NG); NASA ASRS ACN 2303103 and 1909391; Wikipedia, “Diamond DA40 Diamond Star”; FAA Airworthiness Concern Sheet, DA 40 / DA 42 in-flight passenger door separations (October 18, 2024); Diamond Service Information Letter SI40NG-094 / SI40-171 / SIF4-008 / SID4-200 (August 30, 2024); Transport Canada AD CF-2025-30 (issued June 23, 2025, effective July 7, 2025).

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