This slide presentation reviews the precursor analysis for flight and ground based anomaly risk significance. It includes information on accident precursor analysis, real models vs. models, and probabilistic analysis

Groen, Frank

NASA Technical Reports Server

Precursor Analysis for Flight- and Ground- 
Based Anomaly Risk Significance 
Determination 
Frank Groen, PhD 
NASA Office of Safety and Mission Assurance 
Presented at 
Space System Risk Management Symposium 
El Segundo CA, April 2010 
https://ntrs.nasa.gov/search.jsp?R=20100014015 2019-08-30T09:19:29+00:00Z
Need far Precursor Analysis 
a CAlB Final Report (October 2003) 
- Section 6.1 : "The Board notes that although there is a process for 
conducting hazard analyses when the system is designed and a process 
for re-evaluating them when a design is changed or the component is 
replaced, no process addresses the need to update a hazard analysis 
when anomalies occur." 
- Section 7.1: "Signals of potential danger, anomalies, and crktiea8 
information shsu~di, in principle, surface in the hazard identification 
process and be tracked with risk assessments suppo~ed by engineering 
analiyses." 
- Finding 7.4-5: "'Risk informatiasin and data from hazard analyses are no8 
communicated effeckiveiy to the risk assessment and mission assurance 
processes. The Board ~ o u l d  not find adequate application of a process, 
database, or metric analysis tool that took an integrated, systemic view of 
the entire Space Shuttle system.'' 
* 2006 ASAP Annual Report in regards to Safety Management 
- "the ASAP "ioud that ... the Agency, could better gauge the likelihood sf 
Bosses by developing Deading indicators, rather than continuing to depend 
on lagging indicators." 
""Swiss Cheese" Concept of Precursor Analy 
Ordinarily, accidents are prevented by a combination 
-s (human and hardware system features 
prevent accidents) 
... Y 
Same hales due 
to anive fri iurws 
,/A*,# ir 
r* 
- . /- #"+" 
-_ J Other halas due Be, 
latent condinone &_. 
--_ _ (resirlent "pethogeoamX 
Succesa~ve layam of delenms, barr1~3rs and ~ a f a ~ u a r d s  
Complete pathway through cheese represents accident 
Precursor conceived as partial pathway through the 
holes in Swiss cheese 
Precursor analysis then corresponds to learning about 
existence and size of holes 
' ' ~ recurs~r "  Definition 
* Definition of a "precursor" 
- An indication of a problem with the potential to recur 
with more severe consequences 
* Key Attributes: 
- Observation indicates some failure mechanism 
- Same mechanism could occur again 
- The consequences could be more severe than what 
has been experienced 
Anomaliies 
Challenger Severe Burn-through, ET 
containment compromised, 
ebris impacts on Loss of Shuttle 
Columbia - 
Davis-Besse 
NPP 
Containment 
i Other Observed 
Anomalies 
t Severe RCG 
Impact, Loss of 
Shuttle on re-entry 
Significant 
Vessel - Large Loss 0% 
Head Coolant Accident 
Erosion 
How do we focus on risk-significant anamalies? 5 
Exarnp es of Types of Precursors 
A near-miss because of chance or an opportune 
mitigation 
Faults that can become failure conditions without 
correction 
Unexpected trend in test, operation, or maintenance 
Unexpected effects from aging of equipment 
bB Common causes of faults or deteriorations 
A~eident Precursor Analysis 
* Establishes a systematic process for evaluation of flight and 
test anomalies 
- Risk-based evaluation of failure mechanisms 
- Triggered by actual flightltest experience 
- Emphasizes 'imagination' through generalization 
* Provides insight into safety performance 
- Identifies safety-related system vulnerabilities 
- Indicates trends in safety performance 
* Makes safety analysis more experience-based 
- Triggers review/modification of safety models based sn 
analysis findings 
Completeness of represented failure modes 
Failure probabilities and influencing factors 
L---- - - - - - - - - -  Management Decisions 
and Actions Risk Information Input 
Overview of NASA's Accident Precursor Analysis 
Technical Approach 
Operational Definition of Precursor 
Historically, precursor analysis has been focused on 
failures, e.g., at Nuclear Regulatory Commission 
NASA process extends focus to anomalies 
- NASA's databases contain mostly anomalies 
(a defect, fault, or other deviation) 
- NASA has a stronger incentive to prevent any failure 
due to fewer barriers in its space systems 
* Operational definition of precursors: 
Anomalies that upon evaluation are determined to 
indicate a failure mechanism that may pose a significant 
degree of risk 
Process 
T T 
No Further Action 
y Dispositioning Mode 
Mechanism Potential for Potential for 
active within Failure Problem Severe 
subsystem or Potential Conditions Consequences 
component of Concern 
Other failure times I
-- - - - - -. -- -. - - -. - 1 
Otner locatloris oti theaffected system 
Larger fault rnagnlluae E -0 I Anomaly fa~lure mecnantsm - e I 
.:: 
0 1 
b-m I 
- - - - -. - - - - - - - -. -. .- - i 
Disposition Pathways 
Anomalies without obvious risk- or reliability implications 
are removed from consideration using rules-of-thumb 
Failure mechanisms of 
screened-in anomalies 
are determined and 
generalized 
* Dispositioning is based on 
- Generalized problem 
potential 
- Evidence caliber 
Path 2: Observation & Trendin 
Decreasing Evidence Caliber 
13 
PasbabiIisti~ Ana 
Parametric Probabilistic Modeling & Risk Significance 
Assessment 
- Quantify the risk potential for anomalies and GPFs dispositioned 
for Risk Modeling 
- Provides a rigorous assessment of the quantified risk 
significance of the failure mechanism acting within the 
system while also highlighting parametric uncertainties 
of the accident sequences that should be further 
PPM Results 
Anomaly Risk 
".*-- Scenario Development for Events 
Dispositioned for Risk Modeling .,,.-+ ~- * ,- ..*, -.,~ ~ .,"""" *,,, <.",~, , " h * 7  " ,,-.,-, -.-  
.", -.~.-, ,..~* ".,*,, 
-.,",* m."" 
Example Space Shuttle Working Session Results 
/- 
- 
Observation & Trending 
Closing Remarks 
* Accident Precursor Analysis (APA) has been used 
by other govt agencies with positive results (e.g., 
N RC) 
Intended to be applied outside the normal problem 
resolution cycle 
Development of NASA APA methodology will 
continue in 2010 


Precursor Analysis for Flight- and Ground-Based Anomaly Risk Significance Determination

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