REG NASA-LLIS-0012-1991 Lessons Learned - Leak Checks of Critical Systems (Orbiter APU Coolant) After Installation Maintenance or Modifications Which Require System Disconnects.pdf

1、Lessons Learned Entry: 0012Lesson Info:a71 Lesson Number: 0012a71 Lesson Date: 1991-07-08a71 Submitting Organization: JSCa71 Submitted by: L. UnderwoodSubject: Leak Checks of Critical Systems (Orbiter APU Coolant) After Installation, Maintenance, or Modifications Which Require System Disconnects Des

2、cription of Driving Event: During post ascent shutdown of an orbiter OV-102 Auxiliary Power Unit (APU) on shuttle mission STS-2, the unit increased in temperature. Flight data indicated stoppage of coolant (water) flow to the APU. Post flight tests indicated proper operation of the coolant control v

3、alves and no flow restrictions. During disassembly, a coolant inlet filter interface fitting was found to be cross threaded. It was concluded that this fitting leaked during ascent and while on orbit. The leak caused water to flash freeze in the line, blocking the flow. The ice thawed on entry and r

4、emoved evidence of the blockage. Initial installation and maintenance procedures were revised to add leak checks and visual inspection for proper alignment of fittings.Lesson(s) Learned: Inadequate leak check requirements may allow defects such as cross threaded fittings to remain undetected. These

5、defects can cause leakage on critical fluid systems (orbiter auxiliary power unit coolant system).Recommendation(s): Procedural requirements were changed to include leak checks on fittings after initial installation and any time they are opened or disconnected.Evidence of Recurrence Control Effectiv

6、eness: N/AProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Documents Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Space Operationsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Configuration Managementa71 Flight Equi

7、pmenta71 Hardwarea71 Launch Vehiclea71 Parts Materials & Processesa71 SpacecraftAdditional Info: Approval Info: a71 Approval Date: 1993-09-10a71 Approval Name: Ron Montaguea71 Approval Organization: JSC/NS3a71 Approval Phone Number: 281-483-8576Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-