page_title: Mandala Airlines Flight 091
section_title: Investigation
hierarchical_section_title: Mandala Airlines Flight 091 / Investigation
caption_attribution_description: English: Boeing 737's port wing with flaps fully extended for landing Polski: Lewe skrzydło samolotu Boeing 737 z klapami w pełni wysuniętymi do lądowania
context_page_description: Mandala Airlines Flight 091 was a scheduled domestic passenger flight that originated from Polonia International Airport in Medan, Indonesia to Soekarno–Hatta International Airport in Jakarta. On 5 September 2005 at 10:15 WIB, the flight crashed into a heavily populated residential area, seconds after taking off from Medan. There were 149 fatalities.
  Dozens of houses and cars were destroyed, and 49 people perished on the ground. 17 passengers survived the accident, with 100 of those on board known to have died. Most of the survivors are thought to have been seated at the rear of the aircraft, though some of these have reportedly since died from their injuries. Most of the dead were Indonesian. Rizal Nurdin, the sitting Governor of North Sumatra, and Raja Inal Siregar, his immediate predecessor, were among the dead.
context_section_description: The FDR and the CVR were found and sent to Washington to be read out by the 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. However 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.
  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. However, not a single indication of an engine failure was found on the engines. Hence, engine failure was ruled out by investigators.
  The disassembly examination of both engines revealed there was no defect with the engines that contributed to the accident. Observers reported smelling durian fruit in the crash, leading to suggestions that the plane was overloaded with the fruit. The director of the airline initially denied that durian was on board, but later admitted that 2.7 tonnes were loaded. The NTSC confirmed that 2 tonnes of durian were on board. However, weight and balance examination also revealed that the actual aircraft take-off weight and center of gravity met the requirements and standards for take-off performance. The weather itself was not a factor in this accident.
  The official final report on the accident was released by the National Transportation Safety Committee (NTSC) of Indonesia on 1 January 2009. According to it the probable causes of the accident were the following:
  The aircraft took off with an improper take-off configuration, namely with retracted flaps and slats causing the aircraft failed  [sic] to lift off.
  Improper checklist procedure execution had led to failure to identify the flap in retract position.
  The aircraft's Take-off warning system horn was not heard on the CAM channel of the CVR. It is possible that the take-off configuration warning was not sounding.
caption: Fully extended flaps of a Boeing 737
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