Metro cleared a key obstacle Monday to replacing its oldest rail cars, receiving clearance from federal officials just a day before safety investigators are expected to target the cars in a report on last summer's deadly Red Line crash.

The Federal Transit Administration signed off on Metro's plan to spend $886 million to buy 428 rail cars from Kawasaki Rail Car Inc., according to a letter dated Monday by Administrator Peter Rogoff. The transit agency had run into trouble earlier this month meeting federal "Buy America" rules for the 7000 series rail cars.

The requirements mark the latest hurdle for Metro in getting the new cars, which will run on the Dulles Rail extension and replace the nearly 300 remaining Rohr 1000 series rail cars in Metro's fleet.

For years, National Transportation Safety Board officials told Metro to get rid of the Rohr cars because they are not "crashworthy," collapsing upon impact. But Metro had said it couldn't afford to replace or mothball them.

Then, one of those cars crumpled to a third of its size during the June 2009 Red Line crash near Fort Totten, killing nine people. In November, other 1000 series cars suffered the most damage during a slow rail yard crash, even though they were not at the point of impact.

The NTSB is set to release its final findings of the Red Line crash investigation Tuesday, likely focusing on the rail cars in its recommendations.

Metro has been planning to buy new rail cars since it won new federal funding with local matches totaling $300 million per year.

In April, though, the deal was jeopardized when the Metropolitan Washington Airports Authority said Metro was loading development charges on the authority's Dulles Rail cars so the transit agency could get cheaper cars. Metro had to renegotiate.

Then Gov. Bob McDonnell threatened to withhold Virginia's share of the money unless the state could have two of the four Virginia seats on Metro's board. The state capitulated at the last minute.

The day the rail contract was due, the FTA in a letter "expressed serious reservations" about Metro's plan to comply with the Buy America standards.

Kawasaki gave Metro an extension until Aug. 13 to work out the details. Now, after Monday's approval letter, Metro spokeswoman Lisa Farbstein said only paperwork remains to be done and Metro expects to meet the deadline.

The rail cars aren't all slated to arrive until at least 2016.