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APU Fuel Loading. The crew was surprised to learn, before our first launch attempt, that APU fuel was only loaded to approximately 93 percent. Weight and CG were not factors in this decision to load only 92 percent. It has apparently become the "standard", since STS-9, to "light-load" the APU fuel for all flights in order to simplify paperwork. While it may be argued that it is "unlikely" that more than 92 percent of APU fuel would be needed except in an extreme emergency, and while the "extra" APU fuel should certainly be traded off when performance is critical, the potentially catastrophic results of APU fuel exhaustion make the decision to light-load fuel routinely, merely to simplify paperwork, seem questionable at best. It is recommended that the descision to light-load APU fuel routinely be readdressed. 

IN-FLIGHT MAINTENANCE 

CRT changeout. Because of a failure in forward CRT 2, a swap was performed with aft CRT 4 to provide full capability during entry. Access to the back of CRT 2 was made by lowering panel MO58F. The initial attempt to lower this panel was frustrated by tool callouts in the IFM checklist which were correct for OV-099 but not for OV-103. A teleprinter message was later recieved which updated the published procedure. In addition, one of the two captive fasteners holding MO58F was partially stripped, and the second was, in fact, not captive and was lost. This panel was noted to sag during entry as a result of only one tie-down point. 

It was not necessary to remove the IMU manifold to reach the two connectors on the back of CRT 2. The large connector could easily be removed by hand; the small connector, however, could not be accessed even with connector tools until the CRT was loosened from the front and pulled forward approximately two inches to eliminate interference with structural beams. 

Access to the back of CRT 4 was easily made through panel R17. As an afterthought, it was discussed that access could have also been made through R16 to avoid some of the wire bundles associated with R15. Removal of CRT 4 was aggravated by all four mounting fasteners being severely overtorqued. The ratchet wrench was totally unsuccessful in breaking loose any of the fasteners, and the PLT finally resorted to attaching vise grips to an Allen wrench and exerting so much force on each fastener that he was concerned about stripping them. KSC maintenance procedures should be reviewed to ensure that fasteners are properly torqued. 

During reconnection of the large cable in the forward CRT slot to the replaced CRT, it was difficult to confirm that the connection had seated fully and, in fact, on initial power-up the CRT did not work. The PLT attempted the similar connection on the failed CRT in the aft slot to compare the feel. After a second attempt, the connector on the replacement CRT was successfully mated and it functioned properly. A point of interest which was noted during post-flight debriefings is that there is no concern about powering on a previously failed CRT in its holdings (e.g., the original CRT 2 remounted in the CRT 4 slot), since no failures have been identified in which a bad Display Unit can harm a Display Electronics Unit. The converse is not true, however, since a bad DEU can possibly can loss of a CRT