It should name the discipline, describe the supervising professional and how the technologist's work supports that person, set out the applicant's theoretical knowledge and practical experience, state the position, wage and dates, and confirm that the applicant will be an employee rather than a contractor. A one-page offer with a title and salary is not enough.
Draft the letter around the officer's questions
Write the letter in the order an inspector at the port of entry will read it. First, the employer and its business, so the facility is recognizable as an aircraft-component operation with engineering staff. Second, the professional the technologist supports, with that person's title, qualifications and the engineering work performed.
Third, the duties, described as inspection, testing and data preparation in support of that engineering work rather than as generic quality control. Fourth, the applicant's theoretical preparation, listing the diploma, relevant coursework and certification levels, and the years of experience applying them. Fifth, the terms: employee status, wage, location and a requested period of up to three years.
Attach the diploma, transcripts, certification cards and a résumé that uses the same vocabulary as the letter. Reconcile any inconsistent titles across documents before the file is submitted.