As you can see, you can combine a defined benefit plan with a 401k plan. This is done all the time by many different administrators and financial advisors. But don't forget the 6% limitation on the 401(k) plan. Make sure you discuss all the issues of a combo plan with your TPA.
In general, ERISA does not cover plans established or maintained by governmental entities, churches for their employees, or plans which are maintained solely to comply with applicable workers compensation, unemployment or disability laws.
The Employee Retirement Income Security Act (ERISA) covers two types of retirement plans: defined benefit plans and defined contribution plans.
A 401(k) plan allows employees and employers to contribute to a tax-deferred retirement account. However, a defined benefit plan promises employees a specified benefit at retirement and places the risk of providing the benefit on the employer.
Box 13 on the Form W-2 PDF you receive from your employer should contain a check in the “Retirement plan” box if you are covered. If you are still not certain, check with your (or your spouse's) employer.
Setting up a defined benefit plan can be done using an IRS pre-approved plan document issued by an actuary or plan administrator. You should file Form 5500 annually. In addition, Schedule SB should be signed by the actuary and attached to the Form 5500 filing.
Plans must meet minimum ERISA requirements The Department of Labor's Employee Benefits Security Administration currently oversees ERISA. Your retirement plan administrator should be able to tell you whether or not your retirement plan qualifies for ERISA.
Plans that fall under ERISA include defined benefits and defined contributions plans, 401 plans(k), 413b plans, EPSOPs, or profit-sharing plans. ERISA also covers private health plans such as health maintenance organizations (HMOs) and Flexible Spending Accounts (FSAs).