Mandala Airlines Flight 091

The investigation was carried out by the Indonesian [[National Transportation Safety Committee]] (NTSC), with assistance from United States [[National Transportation Safety Board]] (NTSB) and representatives from [[Boeing]] as the manufacturer of the aircraft.<ref>{{citeweb|title=Kedatangan NTSB AS Untuk Bantu KNKT Ungkap Jatuhnya Mandala|url=https://news.detik.com/berita/d-437156/kedatangan-ntsb-as-untuk-bantu-knkt-ungkap-jatuhnya-mandala-|publisher=Detik|accessdate=16 November 2021}}</ref> NTSC had also requested [[Australian Transport Safety Bureau|Australian]] and [[Aircraft Accident Investigation Committee|Thai authorities]] for a readout on the black boxes. According to a member of NTSC, Rita Wijaya, the investigation could take up to one year. She assured that the final report on the crash will be made public.<ref>{{citeweb|title=Pastikan Penyebab Kecelakaan Mandala, KNKT Butuh 1 Tahun|url=https://news.detik.com/berita/d-436372/pastikan-penyebab-kecelakaan-mandala-knkt-butuh-1-tahun|publisher=Detik|accessdate=16 November 2021}}</ref>

The investigation was carried out by the Indonesian [[National Transportation Safety Committee]] (NTSC), with assistance from United States [[National Transportation Safety Board]] (NTSB) and representatives from [[Boeing]] as the manufacturer of the aircraft.<ref>{{citeweb|title=Kedatangan NTSB AS Untuk Bantu KNKT Ungkap Jatuhnya Mandala|url=https://news.detik.com/berita/d-437156/kedatangan-ntsb-as-untuk-bantu-knkt-ungkap-jatuhnya-mandala-|publisher=Detik|accessdate=16 November 2021}}</ref> NTSC had also requested [[Australian Transport Safety Bureau|Australian]] and [[Aircraft Accident Investigation Committee|Thai authorities]] for a readout on the black boxes. According to a member of NTSC, Rita Wijaya, the investigation could take up to one year. She assured that the final report on the crash will be made public.<ref>{{citeweb|title=Pastikan Penyebab Kecelakaan Mandala, KNKT Butuh 1 Tahun|url=https://news.detik.com/berita/d-436372/pastikan-penyebab-kecelakaan-mandala-knkt-butuh-1-tahun|publisher=Detik|accessdate=16 November 2021}}</ref>

Both flight recorders were recovered immediately after the crash and were sent to United States for a read out by NTSB. Even though both recorders were found in good condition, NTSC noted that there was a malfunction on the cockpit microphone (CAM). As such, investigators could not determine the actual situation inside the cockpit due to the poor quality of the cockpit voice recorder.<ref name=”NTSC” />

The FDR and the CVR were found and sent to Washington to be read out by the [[National Transportation Safety Board|NTSB]] in United States. They were found in good condition; however, the team experienced difficulty reading the Cockpit Area Microphone (CAM). The team also found that the channel from the CAM was masked by hum and noise dominating the signal. There were some voices heard on the CAM track; there were a number of step changes in background noise level and character that may have been consistent with an intermittent electrical connection in the CAM wiring circuit. As a result, the team was not able to conclude that the CAM was providing input to the CVR throughout the entire 30 minutes. Such a poor quality in CVR record failure makes it impossible to find out whether the flight crews made proper take-off configuration procedures including checklist execution. Several crew words, cockpit switch activations, engine noise, and cabin chime sounds heard on the CAM channel of the CVR were typically at a volume level much lower than the standard take off warning horn of the Boeing 737-200. The typical sound of the take-off configuration warning was not heard in the CVR CAM channel. The stick-shaker warning (typically as loud as or louder than the takeoff warning horn) was also not heard on the CVR CAM channel.<ref name=”NTSC” />

Knowing that the aircraft had an incident involving one of its engines, investigators tore both engines down to know if there was any abnormalities on them. Not a single indication of an engine failure was found on the engines, and engine failure was ruled out by investigators.<ref name=”NTSC” />

Knowing that the aircraft had an incident involving one of its engines, investigators tore both engines down to know if there was any abnormalities on them. Not a single indication of an engine failure was found on the engines, and engine failure was ruled out by investigators.<ref name=”NTSC” />