1. Source-of-Truth Data Channels

1.1 Carrier-Native Endpoints

• Direct integration with airline developer portals (e.g., Air Canada API, Emirates Skywards API) to pull live baggage policies.
• Sample call:

GET /v/baggage/policy?flightNo=EK201&cabin=Y&origin=DXB&destination=JFK
Authorization: Bearer <token>

• Pros: 100 % fidelity, updated within minutes of policy changes.
• Caveat: Field names vary (weightLimitKg, maxWeightLb, pieces)—normalize with an internal schema.

1.2 IATA-Compliant Feeds

• NDC or Baggage XML messages via BSP Link for 300+ airlines.
• Use case: Multi-carrier itineraries where one call must resolve baggage for all segments.

1.3 Aggregator APIs

• Duffel, Travelfuison, Kiwi: single contract, normalized JSON.
• Latency: 0–72 h behind airline sources—validate via checksum.

2. Implementation Blueprint

2.1 Hierarchical Fetcher

async def resolve_allowance(carrier: str, flight: str, cabin: str):
    """
    Returns allowance dict with confidence score.
    Priority: carrier → iata → aggregator → manual.
    """
    try:
        return await airline_direct(carrier, flight, cabin)
    except (TimeoutError, ValidationError):
        pass

    iata_resp = await iata_ndc(carrier, flight)
    if iata_resp.confidence >= 0.9:
        return iata_resp

    agg_resp = await aggregator(carrier, flight)
    if agg_resp.delta_pct(iata_resp) < 0.05:
        return agg_resp

    return await create_ticket(carrier, flight)  # human review

2.2 Rule Engine

YAML configuration:

carriers:
  QR:
    rules:
      - route: DOH-AKL
        cabin: Y
        allowance: 2PC 23kg
      - route: DOH-LHR
        cabin: J
        allowance: 2PC 32kg
exceptions:
  - carrier: UA
    condition: "is_star_alliance_gold"
    bonus: +1PC

2.3 Cache & Refresh

• TTL map:
  • Airline direct: 6 h
  • IATA: 12 h
  • Aggregator: 24 h
• Webhook listener: subscribe to airline RSS for policy changes.

3. Edge Cases

3.1 Code-Share Segments

SELECT op_carrier AS rule_carrier
FROM segments
WHERE marketing_carrier = 'VS' AND flight_no = 3;
-- baggage follows rule_carrier

3.2 Alliance Logic

• oneworld: allowance follows most significant carrier (MSC).
• SkyTeam: first international markeitng carrier wins.

3.3 Low-Cost Carriers

function ryanairBaggage(route, fareBrand) {
  const base = fareBrand === 'Value' ? 10 : 20; // kg cabin only
  const purchased = await extrasApi.lookupBooking(pnr);
  return { cabin: base, hold: purchased.holdKg || 0 };
}

4. Accuracy Guardrails

4.1 Contract Tests

Feature: Baggage allowance validation
  Scenario: LAX-NRT on JL economy
    Given flight JL62 in cabin Y
    Then hold allowance should be 2×23 kg
    And carry-on should be 1×10 kg

4.2 Drift Detection

• Daily diff report between airline and aggregator data.
• PagerDuty alert when discrepancy > 5 %.

5. Fallbacks

• Embedded iframe: render airline bagggage calculator inside booking page.
• Ops ticket: auto-create Jira task when confidence < 0.8.