Wenzhou’s Black Box: How China’s Train Tragedy Unfolded - China Real Time Report

Until seconds before he plowed the bullet-shaped nose of his locomotive into the rear of another in an accident that killed him and 39 others, Pan Yiheng had no idea he was whizzing along occupied track.

The other train's driver, He Li, knew something was wrong because fail-safe systems had stopped his train, and he was busying himself getting it moving again.

Zhang Hua, the dispatcher coordinating both trains, was juggling at least eight others as well, some of them traveling through a storm of almost 50 lightning strikes per minute on a railway called the Harmony Express.

On the world's largest, fastest and most-modern high-speed railway, July 23 was a Saturday night marked by massive equipment failure that was made worse by incomplete emergency procedures, confused communications and numerous operational missteps, according to a government report on the incident.

The long-awaited report released late Wednesday on the website of China's State Administration of Work Safety provides previously undisclosed details of a train crash near the eastern Chinese city of Wenzhou that raised serious questions about China's high-speed rail ambitions and served as a metaphor for the nation's emphasis on growth. The accident underscored the growing power of China's Twitter-like microblogs, where the nation's voluble online community provided the first reports of the accident in a rural corner of the east-coast city and criticized the government response and lack of disclosure for weeks afterward.

China's online community continued its criticism on Thursday, saying the report put too much blame on officials already in custody over other matters.

The report lacks technical and systemic details that could shed more light on how the accident happened. It doesn't say specifically how a key railway signaling device could be knocked out by lightning, nor what lines of software code resulted in bungled messages being transmitted to train pilots. The report also fails to say whether the entire railway system is riddled with problems like those that caused July's accident, though it discusses how speedy building of the system made it unsafe.

Still, the report is extraordinary in terms of Chinese government disclosures. Over about 50 pages, it details widespread problems with manufacturers and officials. It includes a second-by-second reconstruction of events, including recorded dialogue the pilots and dispatcher.

It also names culprits, starting with the head of the Railway Ministry, Liu Zhijun, who had already been ousted on corruption charges, continuing down to a station technician named Zang Kai, who first noticed malfunctioning railway signals on the fateful night. Neither train driver is implicated in the accident, and the people named in the report couldn't be reached on Thursday for comment.

Around 7:30 p.m. local time, lightning strikes wreaked havoc with signals on a particular section of the Yongwen line north of Wenzhou South Railway station. When fuses burned out in a trackside LKD2-T1 signal assembly designed to carry messages between dispatchers and trains, no one noticed that it was transmitting a "green" signal that the track was open – in fact, the detection system was broken.

Mr. Zang, the station technician, quickly saw that signals on three other adjacent sections of the track – known as circuits – were malfunctioning. The fourth, flashing green, wasn't spotted as malfunctioning.

The first three malfunctions were quickly fixed, though engineers failed to let anyone know. That would set in motion a process where drivers would be instructed to use visual running procedures in these zones and override the electronics that make trains halt at any hint of problems.

At this point, both trains – Mr. He's D3115 from the eastern Chinese city of Hanghzou, and Mr. Pan's D301 – were sitting as scheduled on the same track to Wenzhou waiting for instructions to proceed.

Mr. He, piloting D3115 with 1,072 passengers, was then told by his dispatcher to enter the problematic track circuit zones but to proceed with caution. "If you come across red lights, switch to visual running procedures, and maintain speed below 20 kilometers per hour," he was told by the dispatcher, Mr. Zhang, according to the account.

Indeed, he soon entered the zone no one knew was a problem, where track-circuit problems triggered a fail-to-safe halt to his train. Mr. He tried to get going again by overriding the system, called an Automatic Train Protection, or ATP, but he couldn't immediately so was stuck on the track. Messages between Mr. He and dispatchers also couldn't go through, likely as a result of the faults that knocked out the LKD2-T1.

Around this time, the dispatcher Mr. Zhang saw empty track on his computers– the failed signal on the Yongwen line that was still broadcasting green – and instructed Mr. Pan's D301 from Beijing with 558 people aboard to set off.

The "green" zone was the last section of a series of track circuits around 15 kilometers long, each one of them designed to electronically detect whether a train is on the track. For trains running at 250 kilometers per hour, the line's designated top speed, passing this section would take less than four minutes, though due to the storm trains were running slower than that. The ATP is part of a multipart signaling system that includes track circuits that detect whether there is activity on a particular stretch of track – they don't see or sense other trains ahead like radar might.

After standing more than seven minutes in the zone that was falsely flashing green signals, Mr. He of D3115 managed to override his ATP's fail-safe and get it moving again about 8:29 p.m.. That action apparently made the train appear on the dispatcher's screen for the first time; the false green signal had made him all but invisible.

But it was immediately apparent to dispatchers that D301 was barreling into the zone.

"D301 please pay attention to your operation. Your zone has a train," a dispatcher barks. "There is D3115. Would you please pay attention to your operation? Now the equipment…."

The black box fails to record the full statement.

Under a half-minute later, D301 – traveling at 99 kilometers per hour and with emergency brakes applied – smashed into D3115, likely killing Mr. Pan first and setting off a major crisis on the world's largest high-speed railway.

–James T. Areddy and Yang Jie; follow Jim on Twitter @jamestareddy