Blackbird Investments plans to start work next month on a “pioneering” residential tower, and the pathfinding nature of the project led the city of Des Moines Urban Design Review Board to approve a financial package that will extend for 20 years, including more than $4 million in tax increment finance rebates that will be paid in years 11 through 20, after the developers exhaust a 10-year, 100 percent property tax abatement. After praising the innovative nature of the project, board member Colleen MacRae said she was troubled by the fact that the $80 million, 26-story tower would enjoy 20 years of tax relief. However, she joined in the unanimous vote to support the financial package.