A Q train in Stillwell Avenue Station View Full Caption Flickr/de la Cuna

SHEEPSHEAD BAY — An “abnormal condition” on a train car likely caused a derailment of a Q train with more than 130 passengers on board during the morning rush Friday, an MTA official said Monday.

Wynton Habersham, the senior vice president of subways for New York City Transit, said at the MTA's monthly meeting they believe an "abnormal condition on the truck of the incident car” is the most likely cause of the derailment.

The southbound Q train derailed at 8:58 a.m. on July 21, just south of the Sheepshead Bay station, he said.

Straphangers evacuated the train through a rescue train to the platform, and one passenger, a pregnant woman, was taken to a hospital for evaluation.

In addition to the “abnormal condition,” which he did not detail further, Habersham said there were maintenance issues that contributed to the derailment.

► TIMELINE: A History of Recent NYC Train Derailments

“We found evidence of a failure to follow proper maintenance protocol, resulting in diminished performance of the performance vehicle truck,” he said.

It was the second derailment in the area in recent weeks, sources and transit officials said.

On July 9, a maintenance train derailed at the nearby West Eighth Street stop, a transit source said. However, MTA spokesman Kevin Ortiz said that a train did not derail on that date, but that a "high-rail vehicle" had a mechanical issue.