Core Entities
Flight: flight_id, flight_number, airline_id, origin_airport, destination_airport, scheduled_departure, scheduled_arrival, actual_departure, actual_arrival, status (SCHEDULED, BOARDING, DEPARTED, ARRIVED, DELAYED, CANCELLED), aircraft_id, gate_id. Gate: gate_id, terminal, gate_code (A12), gate_type (domestic, international), is_available, current_flight_id. Passenger: passenger_id, name, passport_number, frequent_flyer_id. Boarding Pass: pass_id, passenger_id, flight_id, seat_number, boarding_zone, barcode, is_boarded. Baggage: bag_id, passenger_id, flight_id, rfid_tag, weight_kg, status (CHECKED_IN, LOADED, IN_TRANSIT, DELIVERED, MISSING).
Gate Assignment
Gate assignment must balance terminal utilization and aircraft type constraints. Algorithm: for each incoming flight, find available gates in the required terminal (domestic/international) that are compatible with the aircraft size. Score candidate gates: prefer gates adjacent to the same airline other flights (improves connection convenience), prefer gates with appropriate jetbridge type for the aircraft. Check gate availability: gate must be free for [arrival_time – 30min, departure_time + 30min] to allow turnaround. Conflict detection: query all flights using the gate and check time overlap. Assign and lock the gate. Reassignment on delay: if a delayed flight conflicts with the next scheduled gate user, trigger reassignment for one of the two flights.
class GateAssignmentService:
def assign_gate(self, flight: Flight) -> Optional[Gate]:
window_start = flight.scheduled_arrival - timedelta(minutes=30)
window_end = flight.scheduled_departure + timedelta(minutes=30)
candidates = self.db.get_available_gates(
terminal=flight.required_terminal,
aircraft_type=flight.aircraft.type,
from_time=window_start,
to_time=window_end
)
if not candidates:
return None
return min(candidates, key=lambda g: self.score_gate(g, flight))Boarding Process
Boarding zones: passengers are grouped into zones (1-5) to reduce aisle congestion. Boarding order: zone 1 (first class, special assistance) first, then zones 2-5 back to front. Boarding pass validation at the gate: (1) Scan barcode. (2) Verify flight matches the gate current flight. (3) Check boarding_pass.is_boarded is false (prevent double boarding). (4) Verify the boarding time is within the allowed window. (5) Set is_boarded = true. (6) Decrement remaining_boarding_count on the flight. API endpoint: POST /gate/{gate_id}/board with the barcode. Boarding starts 45 minutes before departure. Gate closes 15 minutes before departure: passengers not yet boarded are offloaded (bag removal required for safety).
Baggage Tracking
Each bag has an RFID tag scanned at multiple checkpoints: check-in counter, baggage screening (TSA), baggage sorting (conveyor system), loading onto aircraft, arrival carousel. At each checkpoint: scan RFID -> log BaggageEvent(bag_id, checkpoint, timestamp, location). Update bag.status based on the checkpoint sequence. Misconnect detection: if a passenger is rebooked due to a delay, their bags may be on the original flight. Bag tracking system detects: bag is tagged for Flight A, passenger is now on Flight B. Alert the baggage team to retrieve the bag. Lost bag: if the bag has no scan event for 2+ hours, alert the operations team and the passenger. Weight validation: scale at check-in records weight; if over the limit (23kg), charge excess fees.
Delay Propagation
A flight delay creates cascading effects. When Flight A is delayed: (1) Notify passengers via push notification and email. (2) Update the gate display. (3) Check connecting passengers: passengers on Flight A who have a connection to Flight B with less than the minimum connection time (MCT) + delay. For each affected connection: alert the airline operations, possibly hold Flight B. (4) Check crew scheduling: if the delay pushes the crew duty hours beyond legal limits, reassign crew. (5) Gate conflict: if the delayed departure conflicts with the gate next assignment, trigger gate reassignment. Delay cascades can be modeled as a graph: each flight is a node; edges represent connections. Propagate delays through the graph with BFS.
Real-Time Displays and Notifications
Airport display boards (FIDS — Flight Information Display System) show real-time status. Data source: airline operations system pushes updates via Kafka. The airport management system consumes events and updates: database flight records, FIDS displays (WebSocket push to display controllers), passenger mobile app notifications (push via APNs/FCM), airline lounge displays. Update latency target: under 5 seconds from status change to display update. For passenger notifications: only send when status changes significantly (delay > 15 minutes, gate change, boarding open). Filter to affected passengers using flight_id. Notification history stored for compliance.
Asked at: Uber Interview Guide
Asked at: Airbnb Interview Guide
Asked at: Lyft Interview Guide
Asked at: Shopify Interview Guide