rx - how to chain calls ?

rx-error.ts

import {Component} from '@angular/core';
import {Team} from '../../../models/team';
import {Sprint} from '../../../models/sprint';
import {Observable} from 'rxjs/Observable';
import {Http, Response} from '@angular/http';

@Component({
    selector: 'app-test-backlog-agile',
    templateUrl: './test-backlog-agile.component.html',
    styleUrls: ['./test-backlog-agile.component.scss']
})
export class TestBacklogAgileComponent {

    teams: Team[] = [];

    constructor(private http: Http) {
        this.http.get('/data/teams.json')
            .flatMap((response: Response) => response.json())
            .filter((team: Team) => team.agile === true)
            .flatMap((team: Team) => // équivalent du resolve !!!!!
                this.http.get('/data/sprint.json') // URL paramétrée
                    .map((response: Response) => response.json())
                    .map((sprint: Sprint) => {
                        team.actualSprint = sprint;
                        return team;
                    })
            )
            .reduce((teams, team) => {
                teams.push(team);
                return teams;
            }, [])
            // .bufferCount(Infinity)
            .subscribe(teams => {
                this.teams= teams;
            });
    }

}