1、Lessons Learned Entry: 0028Lesson Info:a71 Lesson Number: 0028a71 Lesson Date: 1992-09-11a71 Submitting Organization: KSCa71 Submitted by: Lisa L.MusgraveSubject: Extension of Orbiter Access Arm (OAA) Description of Driving Event: Failure of relay K41 to activate or relay K44 to deactivate will disa
2、ble hardwire safing panel control of both the primary and secondary extend pilot valves A101409 and A101410. The command path for the hardwire safing circuits, which controls the orbiter access arm, runs through these relays. If relay K41 fails to activate or relay K44 fails to deactivate, the OAA w
3、ould not extend. If a failure occurs, the hardwire safing system would not activate the extension circuit and emergency re-extension could not be accomplished.Lesson(s) Learned: Failure of relay K41 or K44 will disable control of primary and secondary extend pilot valves and prevent extension circui
4、t from being activated.Recommendation(s): Design a redundant hardwire control of the primary and secondary pilot valves using individual relays to control each valve function.Evidence of Recurrence Control Effectiveness: N/AProvided by IHSNot for ResaleNo reproduction or networking permitted without
5、 license from IHS-,-,-Documents Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Space Operationsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Facilitiesa71 Flight Equipmenta71 Ground Operationsa71 Hardwarea71 Launch Processa71 Launch VehicleAdditional Info: Approval Info: a71 Approval Date: 1994-06-01a71 Approval Name: James G. Klinea71 Approval Organization: KSC/HEIa71 Approval Phone Number: 407-867-7614Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
