public airlines(): Observable<any> {
       return this.apollo.query({
            query: gql`{
                allAirlines {
                    id
                    name
                    color
                }
            }`,
            fetchPolicy: 'network-only'
        });
    }

    /**
     * Add a new airline
     *
     * @param {Airline} airline
     * @returns {Observable<any>}
     */
    public addAirline(airline: AddAirline): Observable<any> {
        return this.apollo.mutate({
            mutation: gql`
                mutation($name: String!, $color: String!) {
                    createAirline(name: $name, color: $color){
                        name,
                        color
                    }
                }
            `,
            variables: {
                name: airline.name,
                color: airline.color
            }
        });
    }