The derailment on Friday snarled service on the Q and B lines during the morning commute. There were other problems across the system, including subway signal problems in Manhattan and a train with mechanical problems in Queens.

Veronique Hakim, the authority’s interim executive director, said that officials were investigating the derailment, and that it was not immediately clear what had caused it. Ms. Hakim said the train was “lightly loaded” with about 135 people on board.

“We are sorry this occurred this morning,” Ms. Hakim said.

The episode came a day after the authority’s chairman, Joseph J. Lhota, called on Mayor Bill de Blasio to pay more toward the authority’s plans to fix the subway. Mr. Lhota said that he would release an emergency proposal for the subway soon, and that both the state and the city must provide more funding.

Mr. Lhota’s comments echoed Gov. Andrew M. Cuomo, who criticized Mr. de Blasio for playing the role of spectator and argued that the city owned the subway. But transit advocates say the subway is Mr. Cuomo’s responsibility since he controls the authority, selects its chairman and has taken an increasingly hands-on role at the agency.