Kids Remote Control Airplane

Rationale: Child Pilot, Weekend Park Flight scenario: the primary ConOps scenario shows a 25-minute cycle from unbox to packup. If setup exceeds this budget, children lose interest and the product fails its mission.

Rationale: Child Pilot, Weekend Park Flight scenario: the child practices circuits, left/right turns, and figure-eights on first outing. If controls require pre-training, the product loses the unbox-and-fly value proposition.

Rationale: Parent/Guardian, all scenarios: parent performs go/no-go checks before flight, post-crash inspection, and charging monitoring. Must be accessible to non-technical adults.

Rationale: Parent/Guardian, Charging Fire Emergency scenario: charger detected cell imbalance and triggered warnings, allowing parent to intervene. Without cell-level monitoring, a damaged battery reaches thermal runaway on a kitchen counter.

Rationale: Bystanders, H-004 (descent strike): with ~0.25 kg mass and max airspeed ~15 m/s, KE is ~28 J in a dive. Mass and speed limits must keep energy below the 12 J threshold derived from ASTM toy impact safety standards.

Rationale: Bystanders, Signal Loss Failsafe scenario: aircraft behind trees loses signal, failsafe triggers controlled glide. Without this, lost-link aircraft fly unpredictably until battery dies, potentially striking people or property far from the flying site.

Rationale: Manufacturer: product must be economically viable at scale. EPP foam is CNC-cut, electronics are off-the-shelf. Custom ASICs or exotic materials make the price point impossible and kill the product.

Rationale: Manufacturer, Wind Gust Crash scenario: child replaces propeller and glues wing crack in 10 minutes at field. If field repair is impossible, every crash becomes a warranty return, destroying margins and customer satisfaction.

Rationale: Regulators: these are mandatory market-access requirements. Non-compliance prevents legal sale in the US and EU — the two largest toy markets.

Rationale: Regulators: sub-250g threshold is the globally recognized boundary below which recreational model aircraft avoid registration, remote ID, and pilot certification requirements. Exceeding this mass transforms a toy into a regulated UAS.

Rationale: Retailer: single-box packaging simplifies shelf management and prevents missing-accessory returns. IATA DGR Section II compliance is required for air freight — non-compliant packaging forces expensive ground-only logistics.

Rationale: Retailer: age labelling protects retailer from liability if sold to underage child. Missing or unclear labelling triggers retailer compliance audits and potential delisting.

Rationale: Environment as stakeholder, Physical constraint: 15 kt is typical park-flying conditions. 15-25 kt is marginal but the aircraft must remain controllable enough to land safely rather than becoming uncontrollable.

Rationale: Environment as stakeholder, Electromagnetic constraint: parks have WiFi hotspots, Bluetooth speakers, other RC aircraft. FCC Part 15.249 mandates <1W EIRP. If the link cannot coexist, flights near any public space fail.

Rationale: Derived from STK mass limit (<250g for regulatory exemption) and operational need for slow, controllable flight. Below 5 m/s the aircraft stalls in light wind; above 15 m/s kinetic energy exceeds safe bystander impact thresholds.

Rationale: Derived from STK intuitive control need. Three channels is the minimum for controlled 3D flight. 50 ms latency is the threshold above which novice pilots perceive lag and over-correct, leading to pilot-induced oscillation.

Rationale: Derived from STK novice pilot need. Without attitude limiting, a child's instinctive full-stick response to unexpected motion produces 90-degree banks and vertical dives. ±45° bank and ±30° pitch are the thresholds above which recovery requires trained reflexes.

Rationale: H-003 (flyaway) drives SIL 1. 500 ms is the standard RC failsafe timeout (FHSS frame rate ~9 ms means >50 consecutive lost frames). 3 m/s descent rate limits impact energy to ~1.1 J for a 250g aircraft — well below injury threshold.

Rationale: H-002 (LiPo thermal runaway) drives SIL 2. Per-cell monitoring catches cell imbalance — the primary cause of thermal runaway in multi-cell LiPo packs. 45°C thermal cutoff is the industry-standard threshold for consumer LiPo charging per IEC 62133.

Rationale: H-001 (propeller laceration) drives SIL 2. Nylon or flexible polymer propellers fragment rather than cut on impact. The 15 N breakaway threshold is derived from the force at which a rotating 5-inch prop in EPP foam aircraft can lacerate skin.

Rationale: Derived from STK RF coexistence and operational range need. 150 m covers the typical park flying envelope. 1% frame loss is the threshold below which failsafe does not falsely trigger (50 consecutive lost frames needed at 9 ms rate).

Rationale: H-004 (descent strike) and H-005 (exposed wiring). 10 m/s represents a typical crash speed from 10 m altitude in failsafe glide. Battery ejection creates an electrocution and fire hazard; exposed wiring can short-circuit at 20-40A.

Rationale: Derived from STK session time need. 10-minute setup budget leaves 15 minutes for flying and packup within the 25-minute total session. If setup requires tools, downloads, or adult-only steps, the product fails the child-independence requirement.

Rationale: H-002 (battery thermal runaway from deep discharge) and Battery Critical mode. Over-discharging LiPo below 3.0V causes copper dissolution and internal shorts on next charge. Progressive power reduction gives the pilot time to land rather than suffering sudden power loss at altitude.

Rationale: Derived from STK-REQ-010. The 250g threshold is the EASA/CAA open-category micro UAS limit below which no registration, training, or operational approval is required. Exceeding this makes the product illegal to fly in UK, EU, and most CE/UKCA markets without regulatory action from the child's family. Mass budget also constrains design choices throughout — it is the primary driver for integrated ESC/BEC, EPP foam construction, and 2S LiPo selection.

Rationale: Derived from STK-REQ-012 and STK-REQ-009 (regulatory compliance). EN 71 Part 1 and ASTM F963 labelling are legal requirements for toy products sold in EU/UK/US markets. Missing CE/UKCA marking blocks retail distribution. Propeller warning label is specifically required because the propeller is a laceration hazard to fingers (H-004) and the warning label is the last line of defence after physical guards are impractical at sub-250g mass.

Rationale: Addresses H-002 (LiPo thermal runaway after crash): the primary failure pathway is internal cell damage from crash impact that is not visible externally. Thermal runaway typically initiates 3-15 minutes after damage. No existing SYS requirement addressed the user-facing safe-state procedure after unplanned ground contact. The safe state for H-002 requires battery disconnected and isolated in fireproof container — this requirement makes that safe state reachable by a non-technical user. FAA post-crash guidance for UAVs mandates battery disconnection before approach.

Rationale: STK-REQ-001 requires sessions up to 25 minutes; 5-hour transmitter battery life ensures the transmitter is not the limiting factor across a full afternoon of multi-session use, preventing mid-flight power loss that could cause loss of control.