BANGKOK — Enticed by faint pings from the seafloor, Indonesian investigators have determined the general location of the data recorders that will be crucial in discovering what caused the crash of Lion Air Flight 610, one of the deadliest commercial air disasters in years, officials said on Wednesday.
Divers were zeroing in on the so-called black boxes in the muddy waters of the Java Sea, but strong currents hampered the search, said Air Chief Marshal Hadi Tjahjanto, Indonesia’s armed forces chief.
Based on signals from locator beacons attached to the recorders, a 50-strong team of divers was searching a watery square about 11.5 miles on a side northeast of the capital, Jakarta, said Soerjanto Tjahjono, the head of the National Transportation Safety Committee.
“There is a 70 percent likelihood that we will find the black boxes,” said Mr. Soerjanto, whose committee is leading the investigation in a country plagued by aviation accidents. “The other 30 percent will be our prayers.”
Minutes after taking off from Jakarta on Monday morning, in clear weather, the brand-new Boeing 737 Max 8 jet with 189 people on board plunged into the Java Sea. Its brief flight path, as recorded by FlightRadar24, a flight tracking service, was erratic, full of unexplained descents and increases in speed.
Shortly before the crash, the flight crew had requested permission to return to the Jakarta airport. The plane had experienced an unspecified technical issue the night before, during a flight from the holiday island of Bali to Jakarta, but that problem had been resolved, Lion Air executives said.
Determining what specific problem or chain of events led to the crash is almost impossible without the information stored on the cockpit voice recorder and the flight data recorder.
“From our data, accidents in Indonesia are still mainly caused by human factors,” Mr. Soerjanto said. “For technical problems, there are very few. But we still don’t know about this accident.”
Indonesian aviation experts, who examined what they said was the maintenance log from the flight from Bali to Jakarta on Sunday, said the plane had experienced problems with unreliable airspeed readings. While it is difficult to guess what might have caused the crash without the black boxes, aviation experts have raised the possibility that problems with the delicate instruments that gauge speed and altitude could have contributed to the tragedy.
A variety of malfunctions or oversights could lead to inaccurate speed and altitude projections, including electrical glitches or obstructions to the monitoring instruments affixed to the outside of the plane. Part of what is called the pitot-static system, the external probes send three sets of measurements to the flight crew, and any discrepancy between readings is cause for concern, aviation experts said.
Lion Air technicians cleared the flight for takeoff on Monday, and checked the pitot tubes on the outside of the plane, according to the maintenance log viewed by Indonesian aviation analysts. The tubes can be compromised by invading insects or by ice forming during a flight, among other rare complications.
Peter Marosszeky, a longtime aircraft engineer and former senior executive at Qantas, said that while a full investigation of Flight 610’s final hours was needed, the initial evidence was consistent with problems with the pitot tubes. These tubes are particularly vulnerable in hot, equatorial climates like Indonesia’s to being blocked by wasps, he said.
“It’s very hard to see because the wasps go inside the tube and make a mud nest in there,” said Mr. Marosszeky, who is now the managing director of Aerospace Developments, a research and consulting company in Sydney.
In 2013, an Etihad flight that had been on the ground for little more than two hours in Brisbane, Australia, experienced a faulty airspeed reading during takeoff. Australian transport safety investigators later found that wasps had managed to build a nest in a pitot tube during the brief stopover.
“It’s imperative when you park the aircraft that you cover the pitot tubes,” Mr. Marosszeky said.
But the covers also need to be removed before a plane takes off for the tubes to work in flight. In July, a Malaysia Airlines flight left Brisbane, with all three covers still on the probes.
John Goglia, a former board member of the United States National Transportation Safety Board, said that because the pitot tubes of Flight 610 had reportedly been checked during the maintenance that took place hours before Monday’s fated takeoff, investigators will want to know exactly what was done to them.
“Given the fact that the aircraft had a previous problem, one of the first places to check is whether there was the possibility that a mistake was made” in maintenance, he said.
The proper functioning of the tubes could also have been affected if the systems connected to them were touched during maintenance, Mr. Goglia added.
The tubes are covered when a specialized box is attached to them to carry out a safety check, Mr. Goglia said. Again, the instruments must be unsheathed before the plane is flown again.
It is ultimately the pilot’s responsibility to ensure that the covers are off the pitot tubes, aviation experts said. Normally, pilots are supposed to walk around the plane before takeoff and run through a safety checklist, they said.
Given that the flight on Monday morning left before 6:30, this walk-around would most likely have happened before dawn.
“I always carry a strong torch and an extra battery with me to make sure I see things clearly in the dark,” said Budi Soehardi, an Indonesian pilot with 40 years’ experience flying with various carriers, including Garuda Indonesia and Singapore Airlines. “I’m not sure if everyone does that.”
It would have been standard procedure for Bhavye Suneja, the 31-year-old Indian captain of Flight 610, to be shown the maintenance log from the previous night’s flight that recorded the problem with unreliable airspeed.
The 737 Max 8 entered service last year, and the plane involved in Monday’s crash was delivered to Lion Air in August. It was owned by CMIG Aviation Capital, an aircraft leasing company that is a subsidiary of China Minsheng Investment Group, the company confirmed.
It also would have been customary for Mr. Suneja, who had flown with Lion Air for seven years, to have received training before taking the helm of the new model, to learn how it differed from previous versions of the workhorse 737 jet.
But veteran aviators said that what is less common, particularly among low-cost carriers, is for pilots to receive refresher courses on what to do if the flight faces unexpected difficulties, like inaccurate flight data.
Because planes are now so heavily computerized, basic skills like flying a plane without the aid of technology have become a less common art, pilots said.
“People are so intoxicated by automation that they’ve forgotten how to do things in basic mode,” Mr. Budi said.
If Mr. Suneja was dealing with inaccurate speed or altitude measurements, it should have been possible to adjust for the problem, aviation experts said. The Malaysia Airlines flight crew that took off in July with the plane’s pitot tubes covered was able to land again in Brisbane with the help of air traffic controllers and manual measurements.
But in other cases, pitot tube problems appear to have catalyzed pilot confusion that then unspooled a deadly series of events, such as when Air France Flight 447 crashed into the Atlantic Ocean in 2009 and when Birgenair Flight 301 plunged into the sea after taking off from an airport in the Dominican Republic.
To compensate for malfunctioning pitot tubes, pilots must disengage any autopilot systems that are taking in inaccurate readings, and depend on manual controls and visual cues, navigators said. But when flying over water, it is particularly difficult to judge speed by looking out the window.
“They must fly the plane and make decisions in seconds,” Mr. Budi, the veteran pilot, said. “You know, that’s harder than it sounds.”