In 11 years of driving a bus and two decades with the Port Authority, union official Steve Palonis said he has never heard of the type of incident that happened Friday.
Around 6 p.m. that day a female passenger fell out of a Downtown bus through the rear doors, which opened while the vehicle was in motion.
She landed in an intersection and wound up at UPMC Mercy in critical condition.
"We've never had that happen," Mr. Palonis, president of Amalgamated Transit Union Local 85, said Saturday. "The doors just don't open up and you fall out the back door when the bus is moving. It had to be some safety malfunction."
When the woman fell at Stanwix Street and Fort Duquesne Boulevard the bus driver realized what happened, stopped the vehicle and alerted authorities.
Port Authority spokesman Jim Ritchie did not know the nature of the woman's injuries and said Saturday that the most recent condition update he had was from the night before.
The bus, which was on the 22 McCoy route, has been taken out of service and will be inspected. An area of focus will be the door mechanism.
Mr. Ritchie said he did not know when the bus was most recently inspected.
The transit agency did not identify the driver or the victim.
"The doors were closed and when the bus made the turn the doors opened to allow her to go through," Mr. Ritchie said. "That leads to the question of why they came open, and we don't know that yet."
Mr. Ritchie was not sure whether the bus had a rear stairwell or was a low-floor bus, a model in which the bottom of the doors are essentially flush with the floor. He also did not know exactly where the woman was positioned relative to the doors when they opened.
Port Authority bus doors are controlled by the operator except if the emergency release -- there is one near the rear doors -- is triggered.
"It's pretty tough to just manually force the doors open, and they're designed to not allow that to occur," Mr. Ritchie said.
Drivers have a lever that controls the front and rear doors, Mr. Palonis said. The bus can move when the front door is open; that is not the case for the rear doors.
"The rear doors should never open [while the bus is in motion], and even if the driver bumps the door actuator to open, the bus automatically puts the brakes on," Mr. Palonis said. "You can't operate a bus with the rear doors open."
One thing that puzzled Mr. Palonis was why the woman ended up outside the bus. Even if she were standing at the back doors waiting to get off and the doors opened, he said, "You would not go out the door. You'd go against the side wall. It just doesn't happen."
Mr. Palonis said he is aware of instances when a driver pulling up to a stop has moved the lever to open the rear doors, which caused the bus to stop immediately.
"It's a jolt," he said. "It's like an emergency brake."
The transit union has been involved in the investigation since the outset, Mr. Palonis said. It is unclear whether the bus manufacturer will be brought in to consult with the Port Authority, he added.
Jonathan D. Silver: firstname.lastname@example.org, 412-263-1962 or on Twitter @jsilverpg. First Published May 10, 2014 1:41 PM