What should be done if a small aircraft is modified under an STC that applies to special operations?

When a small aircraft undergoes modifications under a Supplemental Type Certificate (STC) related to special operations, the appropriate action is to approve the aircraft for return to service. This is because an STC is a regulatory approval granted by the FAA that allows specific alterations to be made to an aircraft, while ensuring that these modifications meet established safety and performance standards.

Once the modifications have been completed in accordance with the STC requirements, the next step is to verify that the modifications were performed correctly and that they comply with the terms of the STC. If everything is found to be in order, the aircraft is deemed airworthy, which warrants its approval for return to service. This process ensures that the aircraft can safely operate in accordance with its modified configuration.

In the context of this question, the other options do not reflect the appropriate course of action. Rejecting the FAA Form 337 or holding it until recertification would unnecessarily delay the process and could cause additional complications, especially if the modifications are compliant. Revalidating the STC with the original manufacturer is not a necessary step once the modifications have been performed correctly under the STC itself. Therefore, approving the aircraft for return to service is the correct procedure following modifications made under an STC for