havick, see the supplemental guidance in the memo. Neither statute nor regulations apply a meaning to the term so interpretation must come from standard canons of construction. A once-off training flight in a seaplane is unlikely to be taken as meaning a course of study. The DOJ position will clearly treat an initial type rating training programme as a course of study.
Not all alien applicants, for whom TSA security threat assessments and background checks are required, need to complete courses of study. Such applicants are consequently not required to seek admission under a vocational or academic study visa.
You may wish to read the transcript of a house hearing before the subcommittee on transportation security "A decade after 9/11 could American flight schools still unknowingly be training terrorists?" done 18 Jul 2012 (serial no 112-106). See transcript on GPO website here:
https://www.govinfo.gov/content/pkg/...2hhrg79848.htm