ForeFlight Software Engineer Interview Guide

The 60-second brief

A Software Engineer at ForeFlight is responsible for building and maintaining the highly reliable, safety-critical flight planning and navigation applications used by pilots, flight crews, and aviation departments worldwide. Because our products are actively relied upon in the cockpit and during flight operations, engineering here demands an exceptional commitment to precision, performance, and offline-first capabilities. You will work on complex systems that translate massive amounts of geospatial, weather, and aeronautical data into intuitive, real-time visual interfaces and highly optimized APIs. In this role, your work directly impacts flight safety and operational efficiency.

This guide is scoped to a Software Engineer candidate at ForeFlight.

Focus areas

• Coding Assessments (Take-home/Online OA)
• Linked Lists
• Database Concepts / Data Modeling

The ForeFlight interview process

ForeFlight candidates report 5 rounds over 4-6 weeks. The stages below are what candidates describe, not a published process.

Application Review

Initial review of your application to assess qualifications and fit.

What to demonstrate

• Initial review of your application to assess qualifications and fit
• Depth in Coding Assessments (Take-home/Online OA)

How to prepare

• Be able to walk your CV end to end in two minutes, and say why this company specifically.
• Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.

Group Information Session

Recruiters introduce ForeFlight's engineering culture to candidates.

What to demonstrate

• Recruiters introduce ForeFlight's engineering culture to candidates
• Depth in Coding Assessments (Take-home/Online OA)

How to prepare

• Answer aloud and timed: Write a function to find the first non-repeating character in a string and analyze its time and space complexity.
• Answer aloud and timed: How would you detect a cycle in a linked list using constant extra space?

Online Technical Assessment

Timed assessment to evaluate coding skills, following the information session.

What to demonstrate

• Timed assessment to evaluate coding skills, following the information session
• Depth in Coding Assessments (Take-home/Online OA)

How to prepare

• Answer aloud and timed: Implement an efficient search algorithm to locate a specific flight waypoint within an ordered list of geographical coordinates.
• Answer aloud and timed: Design a relational database schema to support a flight tracking application, including tables for flights, airports, and pilots.

Take-Home Coding Assignment

Some teams may provide a practical assignment that reflects real-world tasks.

What to demonstrate

• Some teams may provide a practical assignment that reflects real-world tasks
• Depth in Coding Assessments (Take-home/Online OA)

How to prepare

• Answer aloud and timed: Explain the difference between an inner join and a left join, and describe a scenario where using an index would significantly optimize query performance.
• Answer aloud and timed: How would you design a caching strategy for an API that serves frequently updated aviation weather data to offline-first mobile clients?

Core Interview Rounds

Interactive sessions including live code review, technical discussions, and behavioral interviews.

What to demonstrate

• Interactive sessions including live code review, technical discussions, and behavioral interviews
• Depth in Coding Assessments (Take-home/Online OA)

How to prepare

• Answer aloud and timed: Describe how you would handle database transaction isolation levels to prevent race conditions when two users attempt to book the same flight crew slot simultaneously.
• Answer aloud and timed: Walk us through your implementation of the take-home API assignment. Why did you choose this specific framework or folder structure?

Where candidates lose points

Prepare for the Information Session

The group info session is a unique part of our process. Pay close attention to the company presentation, as it provides valuable context about our culture and products that you can reference in your later interviews.

Handle CORS Policies Proactively

If your technical challenge involves fetching data from a sample ForeFlight API, ensure your local development environment is configured to handle CORS restrictions. Setting up a simple local reverse proxy or using appropriate headers can save you valuable time.

Prioritize Schema Design

For backend roles, do not rush through the database portion of the interview. Spend time defining clear relationships, primary keys, and indexing strategies before writing queries.

Be Ready to Refactor

During code reviews, do not get defensive about your code. If an interviewer suggests a better way to structure a function, embrace the feedback, discuss the pros and cons, and explain how you would refactor it.

Questions & practice

Implement a custom singly linked list and write a function to reverse it in place.

Medium · Coding & Algorithms

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

Given a string containing nested parentheses, write an algorithm to validate if the structure is balanced.

Medium · Coding & Algorithms

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

Write a function to find the first non-repeating character in a string and analyze its time and space complexi

Medium · Coding & Algorithms

Write a function to find the first non-repeating character in a string and analyze its time and space complexity.

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

How would you detect a cycle in a linked list using constant extra space?

Medium · Coding & Algorithms

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

Implement an efficient search algorithm to locate a specific flight waypoint within an ordered list of geograp

Medium · Coding & Algorithms

Implement an efficient search algorithm to locate a specific flight waypoint within an ordered list of geographical coordinates.

Approach

1. Restate the input: its shape, its size, and what is guaranteed about it.
2. Name the brute-force solution and its complexity before improving on it.
3. Choose the data structure from the access pattern, not from familiarity.
4. State the target complexity and say which constraint rules the naive version out.

Follow-up

• How does this change if the input no longer fits in memory?
• What is the worst case, and how likely is it on real data?

Describe how you would handle database transaction isolation levels to prevent race conditions when two users

Medium · Database & System Design

Describe how you would handle database transaction isolation levels to prevent race conditions when two users attempt to book the same flight crew slot simultaneously.

Approach

1. Say what the runtime actually does before reasoning about the code.
2. Name what is shared across threads and what owns each piece of state.
3. Identify the window where an invariant is briefly untrue.
4. Distinguish a value from a reference to it, and say which one you handed out.

Follow-up

• What happens if two callers reach this at the same time?
• Where could this allocate more than you expect?

Explain the difference between an inner join and a left join, and describe a scenario where using an index wou

Medium · Database & System Design

Explain the difference between an inner join and a left join, and describe a scenario where using an index would significantly optimize query performance.

Approach

1. Name the grain you start from and join outward from it.
2. Check whether any join is one-to-many before aggregating, or the sums inflate.
3. Say which index the query would use, and what makes it unusable.
4. Handle the rows that do not match: that is usually the actual question.

Follow-up

• How does the query change if that join becomes one-to-many?
• What happens to this when the table is ten times larger?

Keep soft-deleted accounts from blocking re-registration

Easy · soft delete · unique constraints · engine differences

app_user holds user_id, tenant_id, email CITEXT, password_hash (NULL for SSO principals), email_verified_at, auth_version, status ('invited','active','suspended','deactivated'), created_at, updated_at, deleted_at. Two live accounts for one address inside a tenant must be impossible, but an address freed by a soft delete must be reusable, and the same tenant may delete and re-register it repeatedly. Write the uniqueness DDL for PostgreSQL 16, then the equivalent for MySQL 8 where partial indexes do not exist, and say what each permits once three deleted rows already hold that address.

Approach

1. Start from what is actually unique: not (tenant_id, email), but (tenant_id, email) among live rows. PostgreSQL says that directly — CREATE UNIQUE INDEX app_user_live_email ON app_user (tenant_id, email) WHERE deleted_at IS NULL. A full constraint over the same two columns burns the address permanently the first time someone deletes an account.
2. Keep case-insensitivity in the type or the index, never in the application: CITEXT as given, or UNIQUE (tenant_id, lower(email)) as an expression index where the extension is unavailable. A case-sensitive unique column is exactly how two accounts for one human appear.
3. For MySQL 8 the predicate has to move inside the key: add a discriminator column that is a constant 0 while the row is live and is set to user_id on delete, with UNIQUE (tenant_id, email, deleted_marker). Live rows share the constant and still collide; deleted rows differ from each other and stop colliding.
4. State the NULL variant and its dependency: leaving the marker NULL for deleted rows also works, because a unique index treats NULLs as distinct — true in MySQL, and true in PostgreSQL only under the default NULLS DISTINCT, which PostgreSQL 15 lets you reverse. Check the polarity against the three existing deleted rows: constant-on-live is what preserves the collision you want, and reversing it silently admits duplicate live accounts.

Follow-up

• A deleted account re-registers with the same address the next day. Do the old resource rows follow the new user_id, and how does the API keep the two principals apart?
• How do you honour an erasure request while resource_revision.actor_user_id still references this table?

Design a relational database schema to support a flight tracking application, including tables for flights, ai

Medium · Database & System Design

Design a relational database schema to support a flight tracking application, including tables for flights, airports, and pilots.

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

How would you design a caching strategy for an API that serves frequently updated aviation weather data to off

Medium · Database & System Design

How would you design a caching strategy for an API that serves frequently updated aviation weather data to offline-first mobile clients?

Approach

1. Fix the scope first: who calls this, how often, and what they do when it fails.
2. Name the read and write paths separately; they rarely have the same bottleneck.
3. Choose a partition key and say what query it makes expensive.
4. State the consistency you need, and where you are willing to be stale.

Follow-up

• What breaks first when traffic grows ten times?
• How does this behave when that dependency is down for an hour?

Walk us through your implementation of the take-home API assignment. Why did you choose this specific framewor

Medium · Take-Home & Code Review Discussion

Walk us through your implementation of the take-home API assignment. Why did you choose this specific framework or folder structure?

Approach

1. Say who the caller is and what they do when the call fails halfway.
2. Define the identity of a request so a retry cannot double-apply it.
3. Separate accepted, pending, failed and confirmed; they are different facts.
4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

• What happens if the caller retries after a timeout?
• How does a client discover it is on an old version of this contract?

How does your solution handle API rate limiting or network timeouts when fetching data from external aviation

Medium · Take-Home & Code Review Discussion

How does your solution handle API rate limiting or network timeouts when fetching data from external aviation services?

Approach

1. Say who the caller is and what they do when the call fails halfway.
2. Define the identity of a request so a retry cannot double-apply it.
3. Separate accepted, pending, failed and confirmed; they are different facts.
4. Design the error taxonomy before the success shape; callers branch on it.

Follow-up

• What happens if the caller retries after a timeout?
• How does a client discover it is on an old version of this contract?

If you had to scale your take-home project to handle ten times the current traffic volume, what bottlenecks wo

Medium · Take-Home & Code Review Discussion

If you had to scale your take-home project to handle ten times the current traffic volume, what bottlenecks would you expect to encounter first?

Approach

1. Clarify what is being asked and what a complete answer contains.
2. State your assumptions explicitly before working the problem.
3. Say what you would check first and why it is the highest-information step.
4. Work from the requirement backwards to the design.

Follow-up

• What assumption would you test first?
• How would you know your answer was wrong?

Looking at this sample of Java code, what code smells or potential performance issues do you identify, and how

Medium · Take-Home & Code Review Discussion

Looking at this sample of Java code, what code smells or potential performance issues do you identify, and how would you refactor it?

Approach

1. Clarify what is being asked and what a complete answer contains.
2. State your assumptions explicitly before working the problem.
3. Say what you would check first and why it is the highest-information step.
4. Work from the requirement backwards to the design.

Follow-up

• What assumption would you test first?
• How would you know your answer was wrong?

Every query on one table stalls for forty seconds mid-deploy

Medium · lock contention · ddl · migrations

During a release on PostgreSQL, every query touching resource times out for about 40 seconds and then recovers with no intervention. The release ran one migration, ALTER TABLE resource ADD COLUMN archived_reason TEXT, and the migration log shows it completing in 6 ms. Unrelated tables showed no change in error rate. Explain how a 6 ms statement caused a 40-second stall, give the ordered checks you would run on a live system to confirm it, and give the migration procedure that prevents a repeat.

Approach

1. Separate the statement's duration from the lock's duration. ADD COLUMN with no default is a catalogue-only change and genuinely runs in milliseconds, but it requires ACCESS EXCLUSIVE, and it cannot acquire that until every transaction already touching the table has finished.
2. Account for the queueing, which is the part that surprises people. A lock request that is waiting blocks later requests for conflicting modes behind it rather than letting them overtake, so one long-open transaction holds the DDL and the DDL holds all the traffic. The stall length is set by the longest open transaction, not by the size of the change.
3. Confirm on a live system in this order: pg_stat_activity for that table ordered by xact_start, looking for the oldest transaction and specifically for state = idle in transaction; then pg_locks where granted = false to find the waiter; then join them on pid to name blocker and blocked. pg_blocking_pids() does that join for you and is the fastest single call.
4. Prevent rather than merely time it better. Set lock_timeout to a second or two on the migration session so the DDL abandons the queue after a bounded wait and is retried, instead of holding it for as long as the oldest transaction lives. Be exact about what that buys: queries arriving during the wait still queue behind the pending ACCESS EXCLUSIVE request, so each attempt costs them up to one lock_timeout of added latency. The outage goes from 40 seconds to about one second per attempt, not to zero. Also run migrations away from deploy-time peaks, and put a statement timeout and an idle-in-transaction timeout on the analytics role that opens the long transactions.

Follow-up

• The same release also wants NOT NULL on that column. What is the sequence that gets there without a long lock?
• Your lock_timeout retry fails ten times in a row because the analytics transaction is always open. What do you change?

Suggested practice checklist

Built from the rounds and topics ForeFlight candidates report.

Day 1 — Map the ForeFlight loop

• Write out the reported sequence: Application Review, Group Information Session, Online Technical Assessment, Take-Home Coding Assignment, Core Interview Rounds.
• For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.

Deliverable: A one-page map of the 5 reported rounds, with the weakest marked.

Day 2 — Work Coding Assessments (Take-home/Online OA)

• Spend the session on Coding Assessments (Take-home/Online OA), which ForeFlight candidates report being tested on.
• Write one worked example in Coding Assessments (Take-home/Online OA) and time yourself on it.

Deliverable: One timed worked example in Coding Assessments (Take-home/Online OA).

Day 3 — Work Linked Lists

• Spend the session on Linked Lists, which ForeFlight candidates report being tested on.
• Write one worked example in Linked Lists and time yourself on it.

Deliverable: One timed worked example in Linked Lists.

Day 4 — Work Database Concepts / Data Modeling

• Spend the session on Database Concepts / Data Modeling, which ForeFlight candidates report being tested on.
• Write one worked example in Database Concepts / Data Modeling and time yourself on it.

Deliverable: One timed worked example in Database Concepts / Data Modeling.

Day 5 — Answer out loud: Coding & Algorithms

• Answer aloud, timed: Implement a custom singly linked list and write a function to reverse it in place.
• Answer aloud, timed: Given a string containing nested parentheses, write an algorithm to validate if the structure is balanced.

Deliverable: Spoken answers to 2 reported Coding & Algorithms question(s), under time.

Day 6 — Answer out loud: Database & System Design

• Answer aloud, timed: Design a relational database schema to support a flight tracking application, including tables for flights, airports, and pilots.
• Answer aloud, timed: Explain the difference between an inner join and a left join, and describe a scenario where using an index would significantly optimize query performance.

Deliverable: Spoken answers to 2 reported Database & System Design question(s), under time.

Day 7 — Answer out loud: Take-Home & Code Review Discussion

• Answer aloud, timed: Walk us through your implementation of the take-home API assignment. Why did you choose this specific framework or folder structure?
• Answer aloud, timed: How does your solution handle API rate limiting or network timeouts when fetching data from external aviation services?

Deliverable: Spoken answers to 2 reported Take-Home & Code Review Discussion question(s), under time.

Behavioural preparation

Behavioural rounds judge the decision you made and what it cost.

Tell me about a time when you received critical feedback on a pull request. How did you handle it, and what di

Medium · Behavioral & Team Collaboration

Tell me about a time when you received critical feedback on a pull request. How did you handle it, and what did you learn?

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

Describe a challenging technical conflict you had with a teammate. How did you resolve it to ensure the projec

Medium · Behavioral & Team Collaboration

Describe a challenging technical conflict you had with a teammate. How did you resolve it to ensure the project succeeded?

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

Why do you want to work at ForeFlight, and how do you approach learning about a complex domain like aviation?

Medium · Behavioral & Team Collaboration

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?

Tell me about a time you had to deliver a feature under a tight deadline. What trade-offs did you have to make

Medium · Behavioral & Team Collaboration

Tell me about a time you had to deliver a feature under a tight deadline. What trade-offs did you have to make, and how did you communicate them to stakeholders?

Approach

1. Pick a story where you made the decision, not one where you watched it.
2. State the situation in two sentences and spend the rest on the reasoning.
3. Give the blast radius: what could have broken, and what you measured.
4. Name the disagreement and how you resolved it with evidence.

Follow-up

• What would you do differently if you ran that again?
• How did you know your change caused the improvement?