Your information is correct; professions that require licenses cannot use the LLC form. A professional corporation or a limited liability partnership would be the best way to limit liability.
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As correctly pointed out by colleagues above APC is an option. Best to you.
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You can form an LLP (limited liability partnership) as an engineer.
From the CA Secretary of State's website:
An LLP is a partnership that engages in the practice of public accountancy, the practice of law, the practice of architecture, the practice of engineering or the practice of land surveying, or provides services or facilities to a California registered LLP that practices public accountancy or law, or to a foreign LLP. An LLP is required to maintain certain levels of insurance as required by law.