FAA Proposes Flap Actuator Fix for the Diamond DA50 After Failures Left Flaps Stuck

The FAA has proposed an airworthiness directive for every Diamond DA 50 C after reports of flap actuator failures that left pilots unable to extend the flaps. The notice of proposed rulemaking was published in the Federal Register on November 12, 2026.

DA 50 C is the type-certificate model name for the five-seat, retractable-gear single that Diamond Aircraft sells as the DA50 RG. The FAA estimates the rule would reach 30 US-registered airplanes.

What went wrong with the flap actuator

According to the FAA, investigations found that the flap actuator could interfere with the aileron control system. One report involved reduced aileron control.

Left uncorrected, the agency says, the condition could mean the flaps will not extend, which could limit aileron travel and reduce control of the airplane. That pairing matters on approach, when a pilot wants both full flaps and full roll authority.

The FAA calls the rule an interim action. The cause is still under investigation by Diamond, and the agency says it may consider further rulemaking depending on what that work finds.

What owners would have to do

The proposal follows Diamond Work Instruction WI-MSB 50-016 and Mandatory Service Bulletin MSB 50-016, both dated July 9, 2026. It sets four steps, the first two clocked from the final rule’s effective date:

• Initial inspection within 50 hours time-in-service or 12 months, whichever comes first: check the black slide grommet for displacement and the rod end bearing for a tight fit.
• Modification of the flap actuator within 100 hours or 12 months, whichever comes first.
• Repetitive inspections for a broken torque seal on the jam nuts where the rod end bearing attaches, first within 200 hours or 12 months of the modification, then at the same interval.
• A report to Diamond on the Execution Report form, within 30 days of the work or of the rule’s effective date, whichever is later.

Any discrepancy found in an inspection must be corrected before the next flight. Once the rule takes effect, no unmodified flap actuator could be installed on any airplane.

A torque seal is a stripe of lacquer painted across a tightened nut and the part beneath it. If the nut turns, the stripe cracks, so a broken seal on the jam nuts is a quick visual sign that the rod end connection has loosened.

What it would cost

The FAA prices the work at $85 an hour. The table below gives its estimates per airplane and across the 30-airplane US fleet.

Action	Labor	Per airplane	US fleet
Initial inspection	1 hour	$85	$2,550
Actuator modification	5 hours, plus up to $2,250 in parts	Up to $2,675	Up to $80,250
Each repetitive inspection	1 hour	$85	$2,550
Execution Report	1 hour	$85	$2,550

Europe has required this since July

The FAA proposal adopts EASA AD 2026-0140, issued July 15, 2026, and effective July 31. The DA50 is designed in Austria, so EASA acts first for its state of design and the FAA follows under a bilateral agreement, the same path as the recent DA42 rudder directive.

The compliance times match: 50, 100 and 200 hours, each capped at 12 months. EASA issued its version as a final AD straight away and took comments only afterward, before August 12, 2026.

There are small differences. The FAA text adds the 30-day reporting requirement, and it does not carry over EASA’s 10-hour or 30-day tolerance for lining the repetitive inspections up with other maintenance.

Where Diamond’s instructions say to “discard” parts, the FAA would require them to be removed from service. Neither version names a terminating action, so the repeat checks have no end date while Diamond’s investigation continues.

How to comment

The FAA must receive comments by December 28, 2026, under Docket No. FAA-2026-13809, through regulations.gov, by fax, mail or hand delivery. The agency may change the rule in response before it issues a final AD.

Until a final rule takes effect, the proposal is not binding on US owners. For a primer on why flap systems are built the way they are, see how aircraft flaps work.