ARP4761A Particular Risk Analysis (systems-engineering-safety/arp4761a/particular-risk-analysis)
Use when the task is a particular risk analysis (PRA) per ARP4761A: a
single event that can affect the aircraft or a system as a whole, its
probability and consequences, and the zone mitigations that keep
protected equipment safe.
Domain quick reference
- PRA covers single-event risks that are not internal system
failures: rotor burst, tire burst, bird strike, fire, and lightning.
- Each event has a probability per flight hour; exposure over the
relevant flight time gives the probability that the event occurs at
all during that exposure.
- The analysis combines the event probability with the conditional
probability that the hazard created by the event damages a system,
producing the failure-condition probability contribution.
- Equipment is grouped in hazard zones; containment, separation, and
redundant routing keep protected zones outside the hazard zone.
- PRA results feed the system safety assessment and close against
the failure-condition probability requirements for the severity
class.
Workflow
- List the applicable particular events (rotor burst, tire burst,
bird strike, fire, lightning) and their probability per flight
hour.
- Compute the event exposure probability over the exposure time
with exposure_probability.
- For each hazard created by the event, combine the event
probability with the conditional probability of the failure
condition using conditional_probability.
- Map equipment to zones and check hazard zone overlap with the
protected zones using containment_verdict.
- Add mitigation (containment, separation, redundant routing) where
the verdict is action, then reassess the zone.
- Roll the contributions into the safety assessment and verify the
failure-condition probability budget closes.
Pitfalls
- Using the event probability alone and skipping the conditional
probability that the hazard actually reaches the system.
- Treating containment as absolute when the hazard zone still
overlaps a protected zone.
- Missing events that originate outside the system under analysis
(tires, engine rotors, birds, fire, lightning).
- Double counting a failure condition already covered by the fault
tree or zonal safety analysis.
Behavior contract (gate 3)
The probability combination, exposure, and zone verdict logic is
exercised by the gate 3 contract test:
scripts/test_particular_risk_analysis.py against
scripts/particular_risk_analysis_logic.py (stdlib unittest, offline).
Run:
python3 scripts/test_particular_risk_analysis.py
Compliance
- Standards referenced, not reproduced: ARP4761A text is
proprietary (SAE); summary-only per standards-map.yaml and
brief 06.
- compliance: STANDARDS-REF, gated: false.
1---2name: particular-risk-analysis3description: Use when you must perform or review a particular risk analysis (PRA) per ARP4761A: quantify the probability of a single-event risk (rotor burst, tire burst, bird strike, fire, lightning), combine it with the conditional probability that the hazard leads to a failure condition, and assess hazard zone containment, separation, and redundant routing mitigations. Produces event-exposure probabilities, combined failure-condition probabilities, and zone verdicts for the safety assessment. Trigger: particular risk analysis, rotor burst, tire burst, bird strike, containment, hazard zone, arp4761a, pra.4license: Apache-2.05---67# ARP4761A Particular Risk Analysis (systems-engineering-safety/arp4761a/particular-risk-analysis)89Use when the task is a particular risk analysis (PRA) per ARP4761A: a10single event that can affect the aircraft or a system as a whole, its11probability and consequences, and the zone mitigations that keep12protected equipment safe.1314## Domain quick reference1516- PRA covers single-event risks that are not internal system17 failures: rotor burst, tire burst, bird strike, fire, and lightning.18- Each event has a probability per flight hour; exposure over the19 relevant flight time gives the probability that the event occurs at20 all during that exposure.21- The analysis combines the event probability with the conditional22 probability that the hazard created by the event damages a system,23 producing the failure-condition probability contribution.24- Equipment is grouped in hazard zones; containment, separation, and25 redundant routing keep protected zones outside the hazard zone.26- PRA results feed the system safety assessment and close against27 the failure-condition probability requirements for the severity28 class.2930## Workflow31321. List the applicable particular events (rotor burst, tire burst,33 bird strike, fire, lightning) and their probability per flight34 hour.352. Compute the event exposure probability over the exposure time36 with exposure_probability.373. For each hazard created by the event, combine the event38 probability with the conditional probability of the failure39 condition using conditional_probability.404. Map equipment to zones and check hazard zone overlap with the41 protected zones using containment_verdict.425. Add mitigation (containment, separation, redundant routing) where43 the verdict is action, then reassess the zone.446. Roll the contributions into the safety assessment and verify the45 failure-condition probability budget closes.4647## Pitfalls4849- Using the event probability alone and skipping the conditional50 probability that the hazard actually reaches the system.51- Treating containment as absolute when the hazard zone still52 overlaps a protected zone.53- Missing events that originate outside the system under analysis54 (tires, engine rotors, birds, fire, lightning).55- Double counting a failure condition already covered by the fault56 tree or zonal safety analysis.5758## Behavior contract (gate 3)5960The probability combination, exposure, and zone verdict logic is61exercised by the gate 3 contract test:62scripts/test_particular_risk_analysis.py against63scripts/particular_risk_analysis_logic.py (stdlib unittest, offline).64Run:65python3 scripts/test_particular_risk_analysis.py6667## Compliance6869- Standards referenced, not reproduced: ARP4761A text is70 proprietary (SAE); summary-only per standards-map.yaml and71 brief 06.72- compliance: STANDARDS-REF, gated: false.
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