Metro abruptly halted its phased return of 7000-series railcars to service Thursday afternoon, after deciding the trains needed a more stringent inspection schedule than initially planned.

Metro’s 748 railcars in the 7000 series have been off the tracks since October, following a derailment caused by faulty wheel assemblies. The derailment on the Blue Line did not cause any injuries, but the transit agency pulled the railcars after inspectors found 20 instances of wheels out of compliance.

On Dec. 14, Metro announced it would finally be returning the railcars in phases, with wheel inspections every 7 days (up from every 90 days before the derailment). The first few trains hit the tracks late last week.

Now Metro General Manager Paul Wiedefeld says the wheels need to be inspected every day, and has paused the trains’ return until a new inspection regimen can be implemented.

“While I recognize the pause is unexpected, we are going to continuously evaluate data we are collecting to ensure that we are enhancing safety,” said Wiedefeld, in a statement.

“I feel that requiring a daily inspection is the safest course until we know more and our have an opportunity to review the data we are collecting with the few trainsets now in operation.”

Metro officials made the decision after meeting with Transportation Technology Center, Inc. — a consultant they hired to analyze the root causes of the derailment.  According to Metro, there are “no new issues of concern” but after the meeting officials concluded “in an abundance of caution” that nightly inspections are the “prudent course of action.”

Metro notified the National Transportation Safety Board and the Washington Metrorail Safety Commission of its new inspection plan Thursday afternoon.

Inspecting the trains is no easy job — it involves a lot more than shining a flashlight underneath. It takes a crew of three people six hours to inspect two 8-car trains.

Metro has cleared 210 of its 7000-series cars to return to service, according to a spokesperson. But exactly how many will be in service on any given day will vary.

Metro did not provide any updated timeline for the railcars’ return, or any explanation of how it would be able to inspect railcars so often.

Metro is currently running reduced service due to the limited number of railcars in use, with trains arriving every 12 minutes on the Red Line, every 20 minutes on the Green and Yellow Lines, and every 24 minutes on the Blue, Orange and Silver Lines.

This story was updated to include a comment from a Metro spokesperson.