diff --git a/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/data/FlightDao.java b/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/data/FlightDao.java
index 17ee14cb9..f980891cb 100644
--- a/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/data/FlightDao.java
+++ b/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/data/FlightDao.java
@@ -1,6 +1,6 @@
 package com.bobocode.flight_search.data;
 
-import com.bobocode.util.ExerciseNotCompletedException;
+import com.bobocode.flight_search.service.Flights;
 
 import java.util.HashSet;
 import java.util.Set;
@@ -12,7 +12,7 @@
  * todo: 1. Implement a method {@link FlightDao#register(String)} that store new flight number into the set
  * todo: 2. Implement a method {@link FlightDao#findAll()} that returns a set of all flight numbers
  */
-public class FlightDao {
+public class FlightDao implements Flights {
     private Set<String> flights = new HashSet<>();
 
     /**
@@ -22,7 +22,7 @@ public class FlightDao {
      * @return {@code true} if a flight number was stored, {@code false} otherwise
      */
     public boolean register(String flightNumber) {
-        throw new ExerciseNotCompletedException();// todo: implement this method
+        return flights.add(flightNumber);
     }
 
     /**
@@ -31,7 +31,6 @@ public boolean register(String flightNumber) {
      * @return a set of flight numbers
      */
     public Set<String> findAll() {
-        throw new ExerciseNotCompletedException();// todo: implement this method
+        return flights;
     }
-
 }
diff --git a/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/factory/FlightServiceFactory.java b/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/factory/FlightServiceFactory.java
index d7bac6fad..4ac00cdc5 100644
--- a/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/factory/FlightServiceFactory.java
+++ b/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/factory/FlightServiceFactory.java
@@ -1,7 +1,7 @@
 package com.bobocode.flight_search.factory;
 
+import com.bobocode.flight_search.data.FlightDao;
 import com.bobocode.flight_search.service.FlightService;
-import com.bobocode.util.ExerciseNotCompletedException;
 
 /**
  * {@link FlightServiceFactory} is used to create an instance of {@link FlightService}
@@ -16,6 +16,7 @@ public class FlightServiceFactory {
      * @return FlightService
      */
     public FlightService creteFlightService() {
-        throw new ExerciseNotCompletedException();
+        return new FlightService(new FlightDao());
     }
 }
+
diff --git a/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/service/FlightService.java b/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/service/FlightService.java
index 20a3d79ef..86f3f7d95 100644
--- a/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/service/FlightService.java
+++ b/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/service/FlightService.java
@@ -1,10 +1,9 @@
 package com.bobocode.flight_search.service;
 
-import com.bobocode.flight_search.data.FlightDao;
-import com.bobocode.util.ExerciseNotCompletedException;
-
 import java.util.List;
 
+import static java.util.stream.Collectors.toList;
+
 /**
  * {@link FlightService} provides an API that allows to manage flight numbers
  * <p>
@@ -13,6 +12,12 @@
  */
 public class FlightService {
 
+    private Flights flights;
+
+    public FlightService(Flights flights) {
+        this.flights = flights;
+    }
+
     /**
      * Adds a new flight number
      *
@@ -20,7 +25,7 @@ public class FlightService {
      * @return {@code true} if a flight number was added, {@code false} otherwise
      */
     public boolean registerFlight(String flightNumber) {
-        throw new ExerciseNotCompletedException();
+        return flights.register(flightNumber);
     }
 
     /**
@@ -30,6 +35,8 @@ public boolean registerFlight(String flightNumber) {
      * @return a list of found flight numbers
      */
     public List<String> searchFlights(String query) {
-        throw new ExerciseNotCompletedException();
+        return flights.findAll().stream()
+                .filter(flightNum -> flightNum.toUpperCase().contains(query.toUpperCase()))
+                .collect(toList());
     }
 }
diff --git a/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/service/Flights.java b/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/service/Flights.java
new file mode 100644
index 000000000..b6df8ee3c
--- /dev/null
+++ b/4-0-object-oriented-programming/src/main/java/com/bobocode/flight_search/service/Flights.java
@@ -0,0 +1,9 @@
+package com.bobocode.flight_search.service;
+
+import java.util.Set;
+
+public interface Flights {
+    boolean register(String flightNumber);
+
+    Set<String> findAll();
+}