Designated Airworthiness Representative (DAR) and Designated Engineering Representative (DER)

The FAA designee system, established under 14 CFR Part 183 (Representatives of the Administrator), delegates specific certificate-issuing and approval functions to qualified private-sector individuals. The two most significant maintenance and airworthiness designee categories are the Designated Airworthiness Representative (DAR) and the Designated Engineering Representative (DER).

The Designated Airworthiness Representative (DAR) is authorized under §183.33. DARs are divided into two functional subcategories: DAR-T (Manufacturing, also written DAR-T/MFR) and DAR-F (Maintenance/In-Service, also written DAR-F/MAINT). A DAR-T performs certification functions for production approval holders — conformity inspections during aircraft manufacture, inspections of completed aircraft against type design, and issuance of airworthiness certificates (FAA Form 8100-2) for new aircraft coming off a production line. A DAR-F performs similar functions for in-service aircraft: original standard airworthiness certificate issuance for previously unregistered aircraft, special airworthiness certificate issuance (for experimental, restricted, light sport, and provisional categories under 14 CFR §21.173–21.199), airworthiness certificate transfer for imported aircraft, and conformity inspections for major repairs or alterations when the local FSDO requests independent verification. Both DAR subcategories are appointed by FAA Aircraft Certification Offices (ACOs) and operate under a Letter of Designation that defines the specific functions they are authorized to perform.

The Designated Engineering Representative (DER) is authorized under §183.29. DERs are engineers — typically with aeronautical, electrical, structural, or propulsion backgrounds — who are appointed to review and approve engineering data on behalf of the FAA. A DER's approval is legally equivalent to direct FAA approval of the same data. The categories of DER specialization include: Structures, Propulsion, Systems and Equipment, Radio/Avionics, Engine/Propeller, Flight Test, and Software/Complex Electronic Hardware. A Structures DER can approve structural repair data for a major repair that would otherwise require an FAA ACO engineer's signature. A Radio DER can approve installation data for a new avionics suite being installed under an STC or field approval. DERs may work independently (as contractors for modification centers, repair stations, or operators) or as Organization Designation Authorization (ODA) unit members within larger manufacturers.

The practical workflow for a major repair or alteration involving a DAR/DER typically runs as follows. The A&P mechanic or repair station identifies that a repair or alteration exceeds the minor classification threshold in 14 CFR Part 43 Appendix A. Approved data must be obtained before the work is performed or as part of a field approval. If manufacturer-approved repair data does not exist, the operator contracts a DER to review the proposed repair method and approve the supporting engineering data (stress analysis, material specifications, conformity to applicable airworthiness standards). Once approved, the A&P mechanic performs the repair, and an IA (or the A&P themselves for Part 145 operators with appropriate authority) signs the FAA Form 337 identifying the DER-approved data source. If a conformity inspection of the completed repair is required, a DAR-F may be retained to perform it and verify the work conforms to the approved data before the aircraft is returned to service.

For aircraft imports — increasingly common as U.S. flight schools purchase European-manufactured training aircraft (Diamond, Aquila, etc.) — the DAR-F plays a key role in the bilateral airworthiness agreement (BASA) process. Under the U.S.–EASA BASA and its Technical Implementation Procedures (TIP), EASA-certified aircraft being imported to the U.S. for U.S. registration are validated by the FAA ACO with DAR-F involvement, converting the EASA type certificate and airworthiness certificate to U.S. equivalents.

Flight schools encounter DAR and DER functions most frequently in three scenarios. First, when adding or modifying avionics in training aircraft — installing ADS-B Out equipment under an existing STC requires conformity verification; installing a novel configuration may require DER-approved installation data. Second, following significant damage: a training aircraft that sustains a hard landing causing prop strike and firewall/engine mount damage will require FAA-approved structural repair data before the A&P and IA can return it to service, often necessitating a Structures DER to approve the repair scheme. Third, when importing training aircraft from EASA jurisdictions — the U.S. registration and standard airworthiness certificate issuance typically involves a DAR-F and the local ACO.

For schools building or managing STC-equipped fleets — aircraft with supplemental type certificates for exhaust gas analyzers, terrain awareness systems, or autopilots — the DER-approved installation data underlying the STC is a document that must be retrievable throughout the aircraft's life. During maintenance or ownership transfers, if DER data packages cannot be located, the modification may need to be re-approved or removed, creating significant cost and aircraft downtime.

Aviatize's digital data and records module maintains a per-aircraft repository of all STC, Form 337, and DER-approved data packages associated with that aircraft's modification history. Each major repair or alteration entry in the aircraft's maintenance record is linked to the associated DER-approved data document, ensuring that the supporting engineering approval is always locatable alongside the maintenance record entry rather than filed separately in a paper binder. When the aircraft is sold, refinanced, or moved between bases, the complete modification data package travels with the aircraft's digital record.

For maintenance operations that use contracted DERs or DARs for recurring STC installations or fleet-wide modification programs, Aviatize tracks each designee's authorization scope, Letter of Designation number, and expiry date. This prevents the common error of submitting engineering data for approval to a DER who has allowed their designation to lapse or whose authorized category does not cover the proposed modification — a mistake that invalidates the approval and requires the entire DER approval process to be repeated with a qualified designee.