Design flaw blamed for Portland Aerial Tram incident
Blustery 38 mph winds and a design flaw in the Portland Aerial Tram were blamed for the December failure of a panel that plunged off the tram and hit a pedestrian below, according to a new report.
The uphill roof panel on Cabin No. 2 unexpectedly detached around 11:52 a.m. on Dec. 4, 2018, dropping at least 100 feet and striking Rose Sprauer, a 21-year-old Portland State University student who declined treatment at the time for the small bump found on her head.
As part of a series of fixes, officials say a new-and-improved tether system will be installed, while the tram's sleek, streamlined panels will be bolted to the cabin body.
Until the fix is completed this summer, the tram will stop running entirely when sustained wind speeds climb above 30 mph — though there have been no known wind delays since the policy was created in late 2018.
"We haven't had a wind stop," said Portland Bureau of Transportation spokesman John Brady. "We know it will be an inconvenience if we did have to stop for wind, but we'd rather do that than take any undue risk."
The failure was the first such total "dislocation incident" reported since the tram began ferrying passengers between the booming South Waterfront and Oregon Health & Science University's campus on Marquam Hill in late 2006. It has completed more than 600,000 trips.
The 50-page report, commissioned by the transportation bureau, found that the eight metal latches and back-up carabiner and wire tethers designed to keep the panel in place were flawed from Day 1. Partial failures had seriously loosened the panel twice before, leading to jury-rigged solutions.
"The size of the hardware used in the system indicates that the tether was likely designed to prevent the panel from falling to the ground if a technician were to accidentally drop it during maintenance," according to the report. "The design of the hardware was inadequate to restrain the wind forces on the panel."
Additionally, the Swiss manufacturer, Gangloff Cabins, failed to provide any maintenance procedures or inspection criteria to tram operators. Despite the lack of guidelines, workers regularly removed the tram's decorative panels twice per month, leading investigators with Ridgeline Engineering Co. to decide the incident was not caused by lack of upkeep.
Instead, it was likely the high winds, and possibly the open roof air vents, that caused "uplift," buckling the panel upward and inward.
"While it is impossible to conclusively say why the panel was pulled from the cabin," the report reads, "it seems that the most likely reason the panel came loose was from lack of stiffness of the panel."
Immediately after the incident, workers fashioned a new tether system using commercially available rock-climbing equipment, which was determined to be "far superior" to the original system.
The tram no longer will open its air ventilation system when winds climb above 35 mph.