Federal investigators say the engineer on the Metro-North train that derailed last year as it sped around a sharp curve in the Bronx, killing four people, has a serious sleep disorder.
A medical document made available Monday by the National Transportation Safety Board says engineer William Rockefeller has "severe obstructive sleep apnea."
The NTSB did not say whether the engineer's disorder contributed to the crash. The sleep medicine specialist who conducted Rockefeller's exam wrote in a report that "being a shift worker might have contributed to the accident," according to the documents released Monday.
Apnea can disrupt normal sleep and result in sleepiness. The board-certified sleep medicine specialist who observed Rockefeller called his disorder particularly debilitating, and said dozens of abnormalities were noted in his sleeping pattern over a seven-hour period. He has seen been treated and is improving.
The document says Rockefeller had not been tested for the disorder before the Dec. 1 derailment. He had previously been diagnosed with hypothyroidism, high cholesterol, some vitamin deficiencies and was obese.
Metro-North said it was reviewing the document.
Rockefeller's lawyer and union leader have suggested the engineer nodded off as the train raced toward the site of the derailment. His attorney said he entered a "hypnotic-like daze" and tried to slam on the brakes.
The NTSB said determination of a cause would come in its final report.