OSO-24 — Environmental Conditions
Summary
Compliance route for OSO#24 at SAIL III, requiring the UAS to be designed and qualified for an adverse-environmental envelope specified by the designer in the flight manual. UAS functions/systems/equipment whose failure could directly result in loss of control of operation (per OSO#5 analysis) must be designed and qualified so environment-induced malfunctions are not likely. Five conditions (wind, temperature, pressure altitude, vibration, humidity) must be tested and reported; five more (rain, hail, snow, HIRF, icing) may instead be excluded by flight-manual limitation. Approaches: laboratory tests (DO-160G), flight tests (40 FH or 3 FH × condition × ≥3 flights with 80% exposure), ground tests, or any combination — complemented by analysis/simulation/inspection.
Operation Safety Objective
OSO#24 — UAS designed and qualified for adverse environmental conditions. Designer specifies the qualified envelope in flight manual / equivalent doc. Operator's responsibility under OSO#23 to operate within that envelope and prevent inadvertent flight into adverse conditions.
Means of Compliance
Conditions to be addressed (minimum)
| Condition | Mandatory test? | Notes |
|---|---|---|
| Wind (incl. gusts/cross wind) | Yes | Specify max in m/s |
| Temperature (range) | Yes | Operating temp range |
| Pressure altitude | Yes | Range in hPa |
| Vibration | Yes | "Passed" if no critical failures induced |
| Humidity (max) | Yes | Relative humidity in % |
| Rain | Optional | Test or limit out (mm/hr) |
| Hail | Optional | Test or limit out (g/m³) |
| Snow | Optional | Test or limit out |
| HIRF | Optional | DO-160G §20 OR limit out by flight manual |
| Icing | Optional | Test or limit out (g/m³) |
For not-tested conditions: include explicit limitation in flight manual to prevent exposure during operation.
Test approaches
1. Laboratory testing (§3.1) — DO-160G or equivalent - For each system/equipment that may contribute to LoC, define applicable conditions + test levels based on operational environment / limitations. - Higher-than-minimum test levels permitted to substantiate extended resilience. - Specific battery reference: ASTM F3005–22 (sUAS batteries). - Wind, vibration, pressure altitude generally cannot be confidence-evidenced via lab alone — must also be checked in flight. - Annex I form (DO-160G-tailored) summarises results.
2. Flight test (§3.2) — pick one method: - Method 1: full demo over 40 FH per ASTM F3298-19 §15.2.2.3(4). - Method 2: per-condition campaign — ≥3 FH spread over ≥3 flights for each condition (one flight may cover multiple), per ASTM F3478-20 Annex A1. - Continuous exposure required during test; representativeness met if condition persists ≥80% of flight time. - Stepwise envelope extension allowed via iterative testing; documentation/declaration/flight manual updated each time a limit is expanded. - UAS s/n set: ≥2, ≤10, declared by applicant, each with relevant exposure; adverse effects/failures recorded and used to set environmental limitations. - Specific ASTM F3298-19 cross-references: §7.9.5.3(3) batteries, §16.7.2.1 HIRF design practices, §A2.4.5 icing. - Operational experience may substitute when ≥10 FH of relevant exposure available on same configuration.
3. Ground test (§3.3) - Optional substitute/complement to flight tests for some conditions (rain, humidity, temperature). Setup must produce results representative of in-flight effect.
Specific guidance — HIRF
HIRF environment per EASA AMC 20-158A (10 kHz – 40 GHz, radio/TV/radar/telecoms emitters). Two compliance options: - Demonstrate DO-160G §20 (conducted + radiated susceptibility) at the test levels in Annex I. - Limit by flight manual to prevent flight where the geography includes HIRF sources. Reference: ASTM F3367-21 for simplified methods on HIRF + indirect lightning.
Specific guidance — Lightning (direct & indirect effects)
Qualification not required for the majority of SAIL III products/operations. For peculiarly lightning-exposed operations, designer addresses lightning by specifying applicable limits + appropriate standards.
Annex I — DO-160G qualification reporting form
Per system/equipment: applicable standard, test procedure reference, test title, demonstrated qualification level, evidence document, remarks. Conditions covered: temperature/altitude (ground survival low/high, operating high, in-flight loss of cooling, altitude, decompression, overpressure, temperature variation), humidity, operational shocks/crash safety, vibration, explosion proofness, waterproofness, fluids susceptibility, sand/dust, fungus, salt spray, magnetic effect, power input, voltage spike, audio-freq conducted susceptibility, induced signal susceptibility, RF susceptibility (radiated/conducted), RF emission, lightning induced transient/direct effects, icing, ESD, fire/flammability.
Annex II — Environmental envelope summary (flight manual)
Single table for authority + operator quick reference: condition · tested (Y/N) · max level positively tested · min/max range · units · test method (lab/flight/ground/combination) · remarks (incl. standard applied).
Conclusions
On successful completion of compliance demo and analysis, applicant declares OSO#24 compliance for SAIL III using the authority's declaration form. Compliance evidence (env qualification forms, lab/flight/ground reports) recorded.
Assumptions & Limitations
- Minimum condition list is smaller than traditional type-certification scope.
- Operator (OSO#23) is responsible for staying inside the qualified envelope — applicant defines it but cannot enforce it.
- Lightning qualification typically deferred at SAIL III.
- For un-tested optional conditions, flight-manual limitation is the only acceptable substitute.
References
- EASA Guidelines for Design Verification, Issue 3
- EASA AMC 20-136A (HIRF certification AMC family)
- EASA AMC 20-158A — HIRF environment definition
- EASA MoC for OSO#5 SAIL III — input on systems whose failure could directly cause LoC
- RTCA DO-160G — Environmental Conditions and Test Procedures for Airborne Equipment
- ASTM F3367-21 — HIRF and Indirect Effects of Lightning on Aircraft (simplified methods)
- ASTM F3005-22 — Batteries for sUAS
- ASTM F3298-19 — Design, construction, verification of lightweight UAS
- ASTM F3478-20 — Durability and Reliability Flight Demonstration Program (low-risk UAS)
- ASTM F3120-M-20 §11 — icing reference
Related
- MoC Index
- OSO-03 — Maintenance of UAS — environmental qualification informs life limits
- OSO-05 — System Safety and Reliability — identifies systems requiring env qualification
- OSO-06 — C2 Link — C2 functional performance must hold across the env envelope
Open Questions
- OSO#23 (operator side) provisions are referenced but not in this corpus.