scope:

Description of Driving Event:

During the performance of closed hatch environmental control / life support system (ECLSS) test, Boeing Engineering authorized a deviation to the pre-approved hazardous procedure. The task and procedure to configure the oxygen supply system was to be performed by a subtask document written by a Boeing ground contractor. The subtask document specifically performed the setup, leak check, oxygen supply and shutdown of oxygen systems. The deviated procedure failed to utilize the steps from the subtask document and could have potentially subjected an in-line flex hose lined with Polytetrafluoroethylene to adiabatic compression caused by pneumatic impact. Teflon-lined flex hoses can ignite from pneumatic impacts from tremendous heat build-up. The subtask documents written steps avoid this potential by specific valve configurations and slow system pressurization rates. The written deviation did however; specify the slow delivery of oxygen to the U.S. Lab. No damage occurred to the flight hardware or GSE as a result of operations performed per the deviated procedure.

Root cause: Deviation from approved written hazardous procedure.