scope:

Description of Driving Event:

During the STS-90 flight, two of the internal air circulation fans within the Research Animal Holding Facility (RAHF) failed to operate. To successfully complete the mission, an in-flight procedure was utilized to maintain the required air flow. Upon landing and recovery, an investigation was conducted to determine the cause of the failed fans.

A small (approximately 6.0 X 0.5 X 0.1 inch) cloth/velcro strap was found to have been ingested into the RAHF air flow, and was eventually pinched between the fan blade and the rotor housing causing the fan to stop. The cloth strap came loose from another piece of stowage hardware and was apparently ingested into the RAHF through an opening while one of the removable rodent habitats was being removed or replaced. While the RAHF has an inlet filter over the main air inlet to the unit (that would have stopped this strap), it does not have a filter directly in front of the circulation fans that would catch any debris in the system, regardless of source.