AAE5304 Chap.7 Ground Risk, Air Risk and SAIL
Ground Risk, Air Risk and SAIL
Keep two risk paths separate
Ground Risk Class addresses potential fatalities on the ground through aircraft, operation and population exposure. Air Risk Class addresses encounter probability through airspace, traffic and procedures.
Show every mitigation credit
Intrinsic GRC becomes final GRC through supported ground measures.
Initial ARC becomes residual ARC through accepted strategic measures, followed by the tactical performance appropriate to the remainder.
Use SAIL as a requirement index
Final GRC and residual ARC meet in the matrix to assign SAIL.
That level sets the robustness burden across operational, organisational, personnel, design and manufacturing controls.
Preserve the unmitigated states
Write intrinsic GRC before any reduction and initial ARC before strategic control. Then show each credited step on its own line.
This preserves the amount of safety credit resting on every measure and shows where the analysis returns if one condition is unavailable. A final class without its path conceals dependency and makes change review impossible.
Prove the mechanism and the evidence
A controlled ground area, observer or parachute is a mitigation mechanism, not a complete credit.
State the safety effect, required integrity, assurance evidence, operating limitation, failure indicator and fallback. Access controls need enforceable boundaries and incursion response; observation needs coverage, communication and action; impact reduction needs installed configuration, maintenance and performance evidence.
Unsupported subtraction is not risk reduction.
Keep strategic and tactical air controls distinct
Airspace structure, coordination, timing or route restriction may lower encounter likelihood before flight and lead to a residual ARC. That residual class still determines tactical performance for detecting and avoiding traffic. A quiet time window does not create zero encounter risk.
State who detects a conflict, what information is available, how action is commanded and what fallback applies when detection is unavailable.
Carry conditions through SAIL
The matrix joins final GRC and residual ARC into a requirement index from I to VI; it does not calculate accident probability. Every favourable input remains conditional on credited mitigations.
SAIL then drives robustness for containment and Operational Safety Objectives. When route, population, airspace or aircraft changes, reopen the affected ground or air path before retaining the matrix result.
What this chapter covers
- 01
Intrinsic and final GRC
- 02
Initial and residual ARC
- 03
Strategic ground mitigation
- 04
Tactical ground mitigation
- 05
TMPR and detect-and-avoid
- 06
SAIL and robustness
Worked example · free
Combine final GRC and residual ARC
- 3Show every ground-risk reduction.
- 3Show the air-risk reduction and tactical obligation.
- 4Read SAIL and state evidence dependencies.
Key terms
- Intrinsic Ground Risk
- The ground-risk classification before credited mitigations are applied.
- Residual Air Risk
- The air-risk classification remaining after accepted strategic mitigation.
- Robustness
- The combination of a control's safety effect and confidence that it will perform.
Ground Risk, Air Risk and SAIL FAQ
Why must GRC and ARC remain separate?
They measure different hazards with different inputs and controls. Ground risk concerns consequences to people on the ground; air risk concerns encounters with manned aircraft. Combining them early hides which mitigation changes which hazard and can lead to unsupported credit.
Is SAIL the probability of an accident?
No. SAIL is a classification from I to VI that maps final GRC and residual ARC to the required assurance burden. Higher SAIL means more demanding robustness across controls and evidence; it is not a direct accident probability.
What makes a mitigation credit defensible?
State the safety effect, integrity level, assurance evidence, operating limitation, failure indicator and fallback. A restriction, observer or parachute changes the operation and needs procedures, training, configuration and records. Without those, the subtraction from risk class is unsupported.
When must the SAIL lookup be repeated?
Repeat it after a change alters final GRC or residual ARC, and reconsider every later requirement whose robustness depends on the revised result and its credited controls.
Exam move
Make a two-column ledger. On the left show intrinsic GRC, each ground mitigation and final GRC. On the right show initial ARC, each strategic reduction, residual ARC and tactical performance. Join the columns only at the SAIL matrix. Annotate every arrow with the condition and evidence that permit it.
Remove one mitigation at a time, return to the preceding class and identify which SAIL-derived requirements must be reconsidered. For each reduction, write the safety mechanism, integrity claim, assurance evidence, limitation, failure indicator and fallback. On the air side, separate the measure applied before flight from the tactical response that remains after strategic reduction.
End by stating that SAIL is a requirement index and by naming the operational or evidence burden it drives. This sequence prevents a favourable class from being presented without the conditions that make it valid.
