Crashed Lion Air jet had faulty speed readings on last 4 flights

The Lion Air plane that crashed in the Java Sea last week had faulty airspeed readings during its last four flights and Indonesian investigators called on planemaker Boeing Co. and U.S. authorities to ensure there aren’t fleet-wide issues.

The Southeast Asian country’s National Transportation Safety Committee, which is charged with finding the cause of the crash that killed 189 people, is collecting data on what happened during the three prior malfunctions and the flight crew’s actions prior to the accident, it said in a statement Monday. The agency gleaned the information on the plane’s previous trips from the flight data recorder retrieved from the wreckage last week.

The body asked the U.S. National Transportation Safety Board (NTSB) “and Boeing to take necessary steps to prevent similar incidents, especially on the Boeing 737 Max, which number 200 aircraft all over the world,” it said in the statement.

A spokeswoman for Boeing in Singapore declined to comment. Investigators haven’t revealed reports of other airspeed failures on 737 Max aircraft.

The latest information released by investigators still doesn’t answer why the pilots on three previous flights were able to handle the problem while the crew on Oct. 29 ended up diving at high speed into the sea, said John Cox, president of consulting company Safety Operating Systems and a former airline pilot.

“I’m still of the opinion that losing airspeed on the airplane shouldn’t result in losing the airplane,” Cox said.

Pilots are trained to deal with faulty airspeed readings. There are three separate systems to calculate speed and altitude, and there are a variety of measures pilots can take when speed readings become unreliable.

Greater scrutiny not pursued?

An area that investigators will want to explore is how Lion Air addressed a recurring problem on the plane. If malfunctions continue to occur on a component and routine maintenance procedures don’t solve it, airlines are supposed to have a process to bring greater scrutiny to the issue, Cox said.

“When you see recurring problems, it says the normal easy fixes aren’t solving it,” he said.

While search teams scouring the waters managed to bring up the flight data recorder, a separate recorder that captures cockpit conversations and background noise is still buried in the seabed where the plane plunged. The audio device may be crucial to unraveling what happened during the flight’s final moments. In particular, it may help explain why the crew asked to return to base minutes into the journey.

“We have said there’s a technical problem but we also want to know what they were discussing in the cockpit and what they were doing,” Soerjanto Tjahjono, chief of Indonesia’s NTSC, told reporters on Monday. “Cockpit voice recorder and flight data recorder are both important to reveal the truth in this case.”

The initial readings from the data recorder showing an airspeed malfunction offer the first solid explanation for why the flight appeared to vary its speeds and altitude starting shortly after takeoff.

The plane’s altitude was mostly about 5,000 feet (1,524 meters), but rose and fell repeatedly within a range of a few hundred feet, according to flight-tracking data from FlightRadar24. The speed also fluctuated in a range of roughly 320 to 375 miles (515 to 604 kilometers) an hour, according to FlightRadar24’s data.

Data recorder flying data under investigation

With the data recorder in the hands of investigators, the NTSC has recovered about 69 hours of flying data by the crashed jet during its last 19 trips.

Because Flight JT610 lasted only a few minutes, the voice recorder may also include at least some audio from the previous night’s trip from Denpasar, Bali to Jakarta. The aircraft experienced problems on the flight from Bali with sensors used to calculate altitude and speed.

The instruments were checked by maintenance workers overnight and the plane was cleared to fly, according to Lion Air.

Even with modern GPS tracking, planes need to calculate their precise speed through the air. To determine airspeed — which can vary substantially compared to the speed over the ground due to winds — aircraft rely on Pitot tubes which measure the air rushing into them.

By comparing that pressure against the ambient air pressure obtained from what are known as static ports, the aircraft can determine airspeed. If either of the pressure sensors are blocked, it can cause erroneous readings.

Strong underwater currents, muddy seabed at crash site

Indonesia’s rescue agency said Sunday that wreckage spotted by divers had turned out to be only pieces of skin of the Boeing Co. jet rather than the main fuselage. Strong underwater currents in the Java Sea off Jakarta and a muddy seabed have complicated a week-long hunt that’s involved dozens of ships and hundreds of specialist personnel.

As the 270-square-mile search for debris widened over the weekend, Indonesian authorities broadened a review of Lion Air’s operations, including the airline’s standard operating procedures and flight-crew qualifications. That followed the discovery of defects on two other Boeing 737 Max 8 planes — both operated by Lion Mentari Airlines — during checks on six aircraft of that type. Neither of the faults appeared related to the accident.

The inspection of plane debris indicated the aircraft didn’t explode mid-air before plunging into the Java Sea, Tjahjono said earlier on Monday.

Aircraft broke apart on impact

“The aircraft broke apart under the impact of hitting the water at high speed and it didn’t break apart mid-air,” Tjahjono said. “The engines were still running at high RPM.”

President Joko Widodo has asked airlines to make passenger safety the highest priority, and the government had already ordered a review of Lion’s repair and maintenance unit and suspended several managers.

The transport ministry is coordinating with airport authorities, navigation operators and airlines among others to ensure airworthiness at all airports in Indonesia is well maintained, according to Transport Minister Budi Karya Sumadi.