scope:

Description of Driving Event:

The gaseous nitrogen service coupling of the shuttle orbiter Auxiliary Power Unit (APU) #2 fuel tank was found to be leaking after servicing for shuttle mission STS-3. It was determined that this leakage was the result of contamination/corrosion at the ground/airborne Quick Disconnect (QD). The probable source of the contamination was believed to be a stainless steel filter in the Ground Support Equipment (GSE). Moisture being trapped and held between the filter and its support screens had corroded the filter elements thereby causing the filter to fail and allowing contamination to migrate to the QD's where it was deposited on the poppet seat. Sampling of the fluid had been conducted at the GSE cart upstream of the filter. Investigation has shown that there are many types of contamination and corrosion present in the QD's. Leaking of nitrogen from the APU fuel tank could potentially result in the inability to restart the APU for orbiter re-entry. The following actions were proposed to resolve this problem: (1) modification of the Ground Support Equipment (GSE) to provide for fluid sampling at the GSE/airborne interface, and (2) change the procedures to require filter inspection and replacement on a regular basis.