JAKARTA -- Indonesian budget carrier Lion Air's Flight 610 flew with faulty airspeed sensors and was "not airworthy," according to investigators looking into why the Boeing 737 crashed last month, killing all 189 passengers and crew.
The investigators directed criticism at the airline in their preliminary findings from the monthlong inquiry, published on Wednesday, pressing the company to improve its safety practices. Yet they also said they had still not determined the exact causes of the crash, and would attempt to do so by reconstructing the conditions of the accident in a Boeing facility in Chicago.
The findings by the National Transportation Safety Committee, or KNKT, support previous statements on faulty airspeed and altitude indicators and angle-of-attack sensors in the plane's last few flights -- including the ill-fated one.
Investigators said the plane should have been grounded as soon as problems surfaced on a flight from Bali to Jakarta on Oct. 28, the night before the crash. Instead, the Bali-Jakarta flight was completed. "In our view ... the plane was not airworthy," KNKT investigator Nurcahyo Utomo told reporters on Wednesday. "The pilots should have not resumed the flight."
Still, the investigation has been hindered by searchers' inability to locate the cockpit voice recorder, or second "black box."
"The search for CVR is continuing," Haryo Satmiko, deputy head of the KNKT, said in a press statement on Wednesday. "The investigation will perform several tests including the test of the AOA sensor and the aircraft simulator exercises in the Boeing engineering simulator," referring to the angle-of-attack sensors, which gauge the angle at which oncoming air meets the wings, producing lift.
Lion Air, in the meantime, was told to "ensure implementation of operational manuals in order to improve safety culture." Utomo also told the airline to improve its documentation, pointing out that Lion's record only showed five flight attendants on Flight 610 instead of the actual six.
Flight 610 crashed into the Java Sea on Oct. 29, 13 minutes after takeoff from Jakarta on a scheduled one-hour flight to the island of Bangka.
KNKT investigators earlier said data from the flight recorder showed the plane -- a Boeing 737 Max 8 that had only been in service for two months -- had suffered from a faulty airspeed indicator in its last four flights, including the one that crashed. Lion technicians had replaced one of the plane's AOA sensors to deal with the indicator problem at the airport in Bali the night before the crash.
Boeing on Nov. 6 issued a new safety bulletin for pilots suggesting ways to address erroneous input from an AOA sensor -- supporting reports of a new flight control system in Max 8s that pilots are not familiar with.
The U.S. Federal Aviation Administration said in an emergency airworthiness directive the next day that if an erroneously high AOA sensor input is received by the system, there was potential for repeated nose-down trim commands of the horizontal stabilizer at the aircraft's tail. If not addressed, the condition could make the plane difficult to control and lead to an excessive nose-down attitude, causing the jet to plunge.
Lion has denied that its pilots lacked training for the Max 8, despite using only simulators for Boeing 737 NGs -- the previous 737 series -- in its training center outside Jakarta. The director of the training center, Dibyo Soesilo, said only three hours of computer-based training is prescribed for Max 8 pilots who have been licensed to fly the NG. Lion has since added two more requirements, one of which is that only pilots with a minimum of 500 hours of flying NGs can fly the Max 8, he said.
Indonesia's transportation ministry has admitted a lack of supervision in the burgeoning aviation industry. The newly appointed director general for air transport, Polana Pramesti, said there were fewer than 100 public airworthiness inspectors for around 2,000 aircraft registered at the ministry. She said the ministry was planning to add up to 50 inspectors per year.
With the crash again igniting debate over whether cheap tickets compromise safety, and pending investigation results, Transportation Minister Budi Karya Sumadi earlier said the government was planning to raise the floor for airfares.
The Oct. 29 crash was the first fatal accident for Lion Air since a failed landing in 2004 in Solo, a city in Central Java Province, which claimed 25 lives. But the budget airline had a spotty safety record, with a series of minor incidents as well as runway overruns.
Lion Air Group, which was founded in 1999, has grown into Southeast Asia's largest airline by fleet size on the back of rapidly increasing demand for low-cost flights.