This is my data structure

{
  "profileId":5483,
  "name":"BLA BLA",
  "events":[
    {"id":2554,"typeId":1,"detail":"details follows EN",
      "dates":[
        {"id":2558,"eventDate":"2015-11-20","startTime":"2015-11-20"}
      ]
    },
    {"id":2555,"typeId":2,"detail":"BLA BLA",
      "dates":[
        {"id":2559,"eventDate":"2015-11-21","startTime":"2015-11-21"},
        {"id":2560,"eventDate":"2015-11-22","startTime":"2015-11-22"}
      ]
    }
  ]
}

@for (date of datesForArr.controls; let j = $index; track $index) {
///// datesForArr.controls is null
}

get eventsForArr(): FormArray {
    return this.myForm.get('events') as FormArray;
  }

  get datesForArr() {
    return this.myForm.get('dates') as FormArray;
  }