How the interviewer opens it
“Design a service that shows aircraft positions and flight status worldwide. The service receives observations from several sources and must present fresh, consistent flight tracks.”
The prompt is vague on purpose. The first minutes are for you. Reduce the prompt to the core features and agree on the numbers before you draw.
What to clarify first
- Sources and coverage
- Source volume
- Viewers and read mix
- Latency and availability
- Report contents and disorder
- Flight identity and status
- Consistency
- Coverage gaps and map detail
- Durability and history
- Scope limits
The interviewer has the answers. In a SysRound round, Alex gives these answers, as a real interviewer does.
Scope of a strong answer
Core requirements
- Show current aircraft positions on a world map
- Combine source reports into one current track per aircraft
- Show each flight and its current status
- Show recent positions and the age of the data
Usually out of scope
- Aircraft control or navigation
- Receiver hardware and feed contracts
- Ticket sales and route plans
- Arrival predictions
What interviewers ask about
- Which flight an aircraft serves
- Aircraft serve several flights, while flight numbers repeat and sources can disagree about assignments.
- Conflicting and late position reports
- Report order does not match observation order, and repeated or faulty reports can make a plausible track appear to jump.
- The world map during busy periods
- Many viewers request overlapping areas, but each aircraft moves between areas and each client holds a different view.
Common mistakes
- Uses a flight number or call sign as the permanent identity of a track.
- Uses report arrival order as the order of aircraft movement.
- Treats repeated reports as independent proof that a position is correct.
- Infers arrival when reports stop.
- Serves every map request through a global scan or sends every observation to every viewer.
- Ignores replay effects, map removals, or source clock errors.
The bar by level
- Senior (L5/E5)
- Defines flight assignment rules and source conflict rules. Explains safe replay and map cursor behavior. Uses estimates to control map work and network traffic.
- Staff (L6+/E6+)
- Defines ownership and recovery across regions. Handles uncertain identity and historical corrections without corrupting current tracks. Quantifies freshness, availability, and cost trade-offs during failures.