Arc Skills / Safety
Perform a functional hazard assessment
This task examines what an aircraft or system function can do wrong in its operational context. Arc Skills produces a functional hazard assessment excerpt with separate conditions, effects and assumptions for safety review.
Use this skill
Use Arc Skills to perform an FHA for the named function and operating phases. Start from loss, misleading output, untimely behavior and inadvertent activation before considering component causes.
Inputs:
- Function list and phase definitions.
- Crew alerts, procedures and operating assumptions.
- Project-approved severity criteria and source revision.
Return failure-condition rows with effects, compensating action, evidence gap and follow-on analysis. Propose severity only where the supplied criteria and operational facts support it; do not infer FDAL or item levels.What you provide and what you get
| What you have | How it is used | What you get |
|---|---|---|
| Functions and phases | Defines assessment unit | Failure-condition list |
| Crew/alert context | Tests whether effects differ by response | Assumption record |
| Severity criteria | Supports controlled classification when available | Decision request |
Blank and misleading cabin-pressure indications diverge
Illustrative engineering example.
A synthetic aircraft function displays cabin pressure during climb. A blank screen is obvious to the crew, while a plausible but wrong pressure value may delay recognition. Alert timing and crew procedure are not supplied.
| Failure condition | Possible operational effect | Compensation evidence | Open assessment |
|---|---|---|---|
| Display blank during climb | Crew loses direct pressure indication | Blank state is visibly apparent | Check independent alert and crew procedure |
| Plausible wrong pressure during climb | Crew may trust inaccurate value and delay response | No mismatch alert or detection time supplied | Assess alert latency and operational effect |
| Display updates late | Crew sees stale trend near phase change | Sampling/latency requirement absent | Define acceptable timing from system need |
All three conditions come from one function, but they have different recognition and response paths. Treating “display failure” as one row would hide the difference between obvious loss and misleading information.
The table does not classify severity because the controlled category definitions, alert design and crew response evidence are absent. It also does not translate any later severity into FDAL, IDAL or software level. The safety authority can use these rows to request operational analysis and confirm which conditions need deeper system assessment.
Examine failure behavior in each phase
- State the function from the operator or aircraft perspective and fix the phase.
- Separate no output, wrong plausible output, late output and inadvertent output.
- Record effect, exposure, alerts and crew compensation as evidence or assumptions.
- Apply the project severity scheme only after the relevant operational facts are available.
Questions about this task
Why separate blank from misleading indication?
A blank display may be recognized quickly, while plausible wrong information can be acted on. Their consequences depend on alerts and procedures.
Can this FHA assign software level?
No. The FHA describes function failure conditions; development-assurance allocation is a later, distinct controlled decision.
Sources and further reading
- FAA AC 25.1309-1A: Official system-safety guidance describing functional hazard assessment as a preliminary, function-centered analysis.
- FAA AC 20-174: Official recognition of ARP4754A as an acceptable civil-aircraft development process.