Mandala Airlines Flight 91
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PK-RIM, the aircraft involved in the crash 2 weeks before the disaster.
|Date||5 September 2005|
|Summary||Pilot error (failure to set flaps/slats properly)|
|Site||Medan, North Sumatra, Indonesia
|Fatalities||149 (including 49 on ground)|
|Injuries (non-fatal)||43 (including 26 on ground) |
|Aircraft type||Boeing 737-230 Adv|
|Flight origin||Polonia International Airport
|1st stopover||Soekarno-Hatta Int'l Airport
|2nd stopover||Adisumarmo International Airport
|3rd stopover||Adisucipto International Airport
|Last stopover||Juanda International Airport
|Destination||Ngurah Rai International Airport
Mandala Airlines Flight 91 was a scheduled domestic passenger flight that originated from Polonia International Airport in Medan, Indonesia to Ngurah Rai International Airport in Denpasar via 4 Airports in Indonesia. On 5 September 2005 (10:15 a.m. UTC+7), the flight crashed into a heavily populated residential area seconds after taking off in 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 have reportedly since died from their injuries. Most of the dead were Indonesian, although at least one Malaysian, Ti Teow Chuan from Sabah, was reported dead. Rizal Nurdin, the governor of North Sumatra at the time, and Raja Inal Siregar, the former governor, were among the dead.
Flight 91 is currently the third-deadliest aviation accident in Indonesia, after Garuda Indonesia Flight 152 and Indonesia AirAsia Flight 8501. It was also the second deadliest air disaster in North Sumatra province, the deadliest civilian plane crash in Medan, and the deadliest airplane crash since the loss of West Caribbean Airways Flight 708 earlier that year. Consequently, it was also the deadliest air disaster involving all the Boeing 737-200 series.
3 passengers were Chinese and the rest were Indonesian. All five crew members, 95 of the 112 passengers, and 49 people on the ground were killed. 15 of the 17 surviving passengers were injured. Twenty-six people on the ground were seriously injured in the accident
A passenger named Rohadi Sitepu told Metro TV from hospital that he and five other people seated in the back of the plane in Row 20 had all survived. "There was the sound of an explosion in the front and there was fire and then the aircraft fell," he said. Rohadi said he escaped the blazing wreck by jumping through the torn fuselage and fleeing on foot as four large explosions erupted behind him.
Another survivor, Freddy Ismail, told Elshinta Radio from his hospital bed that the aircraft seemed to be experiencing mechanical difficulties after take-off. "After take-off, the noise of the engine suddenly became very loud and the aircraft began shaking intensely before it suddenly fell," he said.
Aircraft and airline
The aircraft, Boeing 737-230 Adv registration PK-RIM, was built in 1981 and formerly belonged to Lufthansa where it was registered as D-ABHK "Bayreuth" and was acquired by Mandala in 1993. The aircraft was 24 years old by the time of the accident. It had a Certificate of Airworthiness valid until November 2005. The aircraft had involved in an incident before the crash. On 29 January 2003, while rolling to take off from Achmad Yani International Airport in Semarang, the left engine caught fire. The tower tried to inform about the condition to the crew, but since the pilots were busy, they didn't respond. After the aircraft was airborne, the tower repeated the information and the pilots answered, explaining that the No. 1 engine had failed. The pilot said that they would make a right turn to base. The aircraft landed safely. After inspection, it was found that the No.1 engine was covered by animal wool.
Mandala Airlines was established in 1969 and is one of several low-cost airlines that serve the vast Indonesian archipelago. At the time of the accident it was 90-percent owned by a foundation set up by the Indonesian Army strategic reserve Kostrad (Komando Strategis Angkatan Darat). In 2006 it was acquired by Cardig International and Indigo Partners. It has 1,000 employees (at March 2007).
Flight 91 departed for Soekarno-Hatta Airport, Jakarta from Medan. The plane's previous flight was from Jakarta and arrived at Medan uneventfully. The same crew had the flight scheduled on the same day and returned to Jakarta. The flight was a regular scheduled passenger flight and was attempting to take-off from Polonia Airport, Medan, North Sumatera to Jakarta, and it was the second trip of the day for the crew.
At 10.02 WIB, Flight 91 received clearance for take-off with additional clearance from ATC to turn left heading 120 and maintain 1500 ft. The crew read back the clearance heading 120 and maintaining 1000 ft. The ATC corrected the clearance to “one thousand five hundred feet.” The crew re-read it back as 1500 ft. The plane later took off. Some of the passengers and other witnesses stated that the aircraft had lifted its nose in an up attitude and take off roll was longer than that normally made by similar airplanes. Most of them stated that the aircraft nose began to lift-off a few meters from the end of the runway. The ATC tower controller recalled that after rotation the plane began to “roll” or veer to the left and to the right. Eyewitnesses on the ground also reported the same. Witnesses stated that the plane shook violently (possibly indicating a stall). The airplane then overran the departure end of Runway 23, impacted several approach lights, traveled through a grass area and over a river. Some witnesses on the ground recalled that the airplane left wing struck a building before it struck in the busy road, then heard two big explosions and saw the flames. As the airplane came to rest, it fractured into three parts. The airplane was considered a total loss due to the impact forces and post-crash fire. The aircraft had been separated due to impact along the flight track beginning from the end of the runway 23, and then the aircraft came to a halt 540 m from the end of runway. Most of the fuselage section was destroyed by post-impact fire. The remaining part of the fuselage was only the tail section. Both engines detached from the aircraft due to the impact to the ground. The right engine was found about 300 m and the left engine about 400 m from the end of the Runway 23.
At 10.25 AM local time, the ATC declared the airport closed. The airport fire brigade immediately responded to the crash bell activated by the ATC. When they arrived at the end of Runway 23 they realized that the crash site was outside the airport perimeter, and there was no access road to reach the accident site. When they arrived, the fire was still burning at the crash site. Several fire fighting units of the local government and ambulances participated in rescue operation. The local people, police and others were involved in the first hour of the rescue, and later on the Indonesian Air Force and Army asisted. Some victims were evacuated using commercial as well as private cars; it was due to the late arrival of the ambulances at the crash site and their limited number.
At the crash site, there was no person in charge as the coordinator among the rescue teams. The overly crowded situation caused difficulties for the rescue teams in evacuating the victims. According to the witnesses, there were no labels for the victims and no triage area set-up as mentioned in the AEP. Moreover, the rescue team did not know where the uninjured passengers should be transferred to the collection area. The records/labels and the location of the victims were not well documented. The local people tried to rescue one of the pilots; however they were unable to release the pilot from his harness. It was because they were not familiar with aircraft components. While they were trying to save the pilot, the fire blast suddenly came from behind. When they saw the fire, they ran away to avoid the flames. According to them, one of the pilots was still alive at the time they found him. However, after the fire was extinguished, the pilot’s body was not found. The pilot seat was totally burnt. A person who stood close to a store saw that the fire started a few minutes after the aircraft crashed. He could not recall the exact time of the crash. He tried to rescue one of the victims to avoid the fire. According to other witnesses, the fire started a few minutes after the crash.
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 enginse, 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 prized 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.
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- NTSC final report, p.3
- NTSC final report, p.2
- "Aviation Safety Network".
- Richard Lloyd Parry (6 September 2005). "At least 149 die when jet crashes into city moments after take-off". The Times. London. Archived from the original on 4 June 2011.
- NTSC final report, p.7
- "INDONESIAN AIRCRAFT ACCIDENT/INCIDENT DATABASE-YEAR 2003".
- Irwan Firdaus, Associated Press (5 September 2005). "Indonesian Airliner Crashes into City Killing 147". Sarasota Herald Tribune. Retrieved 24 July 2012.
- "Misteri Durian 2 Ton di Mandala Airlines". Suara Merdeka (in Indonesian). 11 September 2005. Retrieved 24 July 2012.
- "Dirut Mandala Akui Angkut 2,7 Ton Durian". Suara Merdeka (in Indonesian). 28 September 2005. Retrieved 24 July 2012.
- "Aircraft Accident Report" (PDF). NTSC. p. 40.
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