The frightening derailment of an A train Tuesday morning, leaving dozens of subway riders injured, was not caused by a track defect or decaying infrastructure, but rather "human error," the MTA said last night.

MTA Chairman Joe Lhota released a statement at 11:15 p.m. on Tuesday (his fifth day on the job), "The preliminary investigation of Tuesday morning's A train derailment indicates the cause was an improperly secured piece of replacement rail that was stored on the tracks; the cause appears to be human error, not a track defect."

Storing equipment in between tracks is a common practice employed by railroads across the country to accelerate rail repairs. The key to this being an effective and safe practice is making sure that the extra equipment is properly bolted down, which does not appear to have happened in this case.

NYCT is inspecting every inch of rail to ensure that each and every replacement part is properly stored and secured. Nothing is more important than the safety of our customers. The investigation into this incident continues.

Earlier in the day, Lhota had said that the agency was investigating why the emergency brake was activated before the derailment. For riders along the A, B, C and D lines, the commute was complicated.

Around 9:45 a.m. on Tuesday, the fourth and fifth cars of the southbound A train derailed. Passenger Skip Suva told us, "We were between 135th and 125th and... the train started shaking insanely violently, the lights started flickering. I was leaning against the left door, on the left side of the train, and the right door was ripped open. I don't think anyone was hurt."

"I will vouch for reports that the train left the rails," another passenger, Mary Hodges, said. "No doubt. We were in the air. I'm pretty sure we scraped the sides of the tunnel wall. But I couldn't swear it."

Kevin Kopp, who was on the second to last car of the train, described the chaotic situation, "It was a bit of a rough ride. Then it felt like the train was jumping. I was like, 'This is serious.' All of a sudden, I saw what I thought was a flash or explosion. I wasn't sure. It all happened so quick. A car went off, then the train stopped. People were screaming. It was chaos... People were throwing up, people were screaming. I thought I might be caught in some fire. I was terrified."

WABC 7 reports, "[T]he rail work was overnight Monday and the rail apparently stayed in place during the entire morning commute. The union representing transit workers claims the old rail and unused pieces of the replacement rail were correctly secured in the center of the track, per protocol."

Governor Cuomo said the derailment was "an unacceptable manifestation of the system's current state... It is my expectation that with new leadership brought by Joe Lhota, the MTA will address the fundamental issues plaguing the transit system and overhaul the organizational structure of the MTA."

Cuomo, who is in control of the MTA, has lately wondered who is in control of the MTA, while demanding more control.