(a) With respect to any company or person principally engaged in business other than carrier business, but which, in addition to such principal business, engages in some carrier business, the Board will require submission of information pertaining to the history and all operations of such company or person with a view to determining whether some identifiable and separable enterprise conducted by the person or company is to be considered to be the employer. The determination will be made in the light of considerations such as the following:

(1) The primary purpose of the company or person on and since the date it was established;

(2) The functional dominance or subservience of its carrier business in relation to its non-carrier business;

(3) The amount of its carrier business and the ratio of such business to its entire business;

(4) Whether its carrier business is a separate and distinct enterprise.

(b) In the event that the employer is found to be an aggregate of persons or legal entities or less than the whole of a legal entity or a person operating in only one of several capacities, then the unit or units competent to assume legal obligations shall be responsible for the discharge of the duties of the employer.