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Safety analysis of aircraft systems

Safety analysis of aircraft systems. In aviation, safety is defined as the absence of accidents and incidents. JAR 25 treats systems as a whole. Acceptable accident rates must be established, 100% safety can never be guaranteed.

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Safety analysis of aircraft systems

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  1. Safety analysis of aircraft systems • In aviation, safety is defined as the absence of accidents and incidents. • JAR 25 treats systems as a whole. • Acceptable accident rates must be established, 100% safety can never be guaranteed. • A relationship must be established between severity of effect and probability of occurrence.

  2. Probability versus severity of effect

  3. The principle of graceful degradation • In any system the failure of a single element, component or connection should not prevent continued safe flight and landing. • This single failure should also not lead to an unacceptable workload for the operating crew.

  4. Types of failure to be considered • Single active failure • Passive and undetected (dormant) failures • Combinations of independent failures • Common-mode failures • Cascade failures • Failures produced by the environment

  5. Errors • Design errors • Manufacturing errors • Maintenance errors • Pilot mismanagement • Errors in manuals or checklists

  6. Dormant failure • Reverser is deployed! • Lauda Air B767 , 26-5-1991 • Design errors in the thrust reverser electric systems led to unobserved deterioration of the HIV valve

  7. Common-mode failure • Whatever you do, keep us away from the city!” • UA 232, 19-6-1989, Sioux City, Iowa. • No. 2 engine fan disc disintegration severed all 3 hydraulic lines in the tail area. • Exceptional flying by the crew led to a landing at Sioux airport

  8. Cascade failure • THY 981, 3-7-1974, Paris • Inadequately closed lower deck door opened, causing floor collapse • This blocked the flying control runs under the floor, causing catastrophic failure

  9. Failure rates in light single engined aircraft • Engine failure. A minimum demonstrated flying speed must be 61 kts or below, to enable a succesful off-airport landing. • Instrument systems for IFR operations must be dual and independent. Vacuum pump MTBF 700 hrs. • Prevention of flap asymmetry must be adequate

  10. A few examples • Cessna 172. Seat rails, flap system, elevator control • Piper PA 28 wing attachment • Robinson R22 helicopter, mast bumping

  11. Current concerns for GA • Inadequate training • Inadequate currency • Insufficient pilot ability • Lack of familiarity with the full flight envelope • Inadequate understanding of increasingly complex systems

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