public FlightRecordBuilder withPassengers(Collection<Passenger> passengers) {
   for (Passenger p : passengers) {
     this.passengers.add(p.getUTI());
   }
   return this;
 }
 public FlightRecordBuilder withPassenger(Passenger p) {
   this.passengers.add(p.getUTI());
   return this;
 }
 public void addPassengers(Collection<Passenger> passengers) {
   for (Passenger p : passengers) {
     this.passengers.add(p.getUTI());
   }
 }
 public void removePassenger(Passenger p) {
   this.passengers.remove(p.getUTI());
 }
 public void addPassenger(Passenger p) {
   this.passengers.add(p.getUTI());
 }