Wednesday, November 28, 2018

Lion Air’s deadly flight was a 13-minute struggle between man and machine

Indonesian investigators released a preliminary crash report on November 28 that described a battle between the pilots of Lion Air flight JT610 and an automated anti-stall system on the Boeing 737 Max 8 aircraft that continually forced the plane downward in reaction to incorrect flight data. Less than 15 minutes after the flight took off from Jakarta on Oct. 29, the plane crashed in the Java Sea, killing all 189 people on board.
The anti-stall system is known as the Maneuvering Characteristics Augmentation System (MCAS), and is a new addition on the 737 Max 8 and 9 models that can pitch the plane’s nose down without pilot input when sensor data indicates the possibility of a stall.

The 78-page report from Indonesia’s National Transportation Safety Committee, known by the acronym KNKT, described in detail problems experienced with the plane in flights before its crash, and shared information from the flight’s data recorder—the cockpit voice recorder hasn’t been recovered—without drawing conclusions. “When it comes to faulting, I don’t know, our job isn’t to find faults,” Nurcahyo Utomo, who heads KNKT’s aviation-accident subcommittee, said at a press conference (paywall).

In addition to Indonesian investigators, the crash probe involved the US National Transportation Safety Board and investigators from Australia and Singapore.

The report made few safety recommendations other than calling on Lion Air to improve its safety culture. It said that in the penultimate flight, pilots continued flying even though the stick shaker—which generates a noisy warning before a stall—continued to vibrate, instead of opting to land at the nearest airport.

On the final flight, according to the Satcom Guru website run by Peter Lemme, a former Boeing engineer, the flight data recorder information for the JT610 showed “there are 26 occurrences of MCAS trim down, pilot trim up”—with trim referring to the efforts to redirect the plane.

A chart included in the report shows a series of orange lines that designate the automated system’s efforts, matched by a series of blue ones in the opposite direction, indicating the pilots’ efforts.
The Oct. 29 crash was the first such incident with the 737 Max variant, which Lion Air was the first carrier to begin using in 2017. This particular aircraft had only been put into operation in August—the flight recorder included 69 hours of operation for 19 flights, including the final one.

According to the crash report, on that flight the shaker indicating an impending stall activated at about 400 feet. The flight system carried out three maneuvers to adjust the nose downward, but the commanding pilot initiated steps to override it a little over eight minutes into the flight. The flight landed safely in Jakarta about an hour and a half after takeoff.

It’s not clear why pilots of the Oct. 29 flight weren’t able to override the system or what procedures they tried to use. According to today’s report, the 31-year-old Indian commanding pilot of JT610 had more than 6,000 hours of flying experience, while the second-in-command, a 41-year-old Indonesian national, had over 5,000 hours of flying experience.

The crash has turned attention to Lion Air’s safety record and lapses, including a plane’s wing clipping an electricity pole in the days after the crash.

Boeing may be working with the FAA on a software update for the system. It’s also addressing pilot questions about how the system is designed, said captain Tajer, noting that many are now keen to know more about the software. He says pilots are trying to understand why the system appears to be set up to engage based on a single data source. They’re also asking why, after engaging once automatically, the system keeps triggering repeatedly without in some way seeking confirmation of a stall, perhaps via another sensor or pilot input.
28/11/18 Tripti Lahiri/Quartz

0 Comments: