A dive from cruising altitude is a mystery

Everything on China Eastern flight MU5735 was routine on Monday. A one and a half hour jump from Kunming in southwest China to the 15 million metropolis of Guangzhou (formerly Canton) in the Pearl River Delta, not far from Hong Kong. Travel within China is currently restricted due to renewed corona outbreaks. According to data provider flightaware, the number of domestic flights last week was just a third of the same week in 2019.

Chinese allowed to travel domestically currently need negative PCR test results. The almost seven-year-old Boeing 737-800 used on the flight was therefore not fully booked, only 123 of 162 seats on board were occupied, and there were nine crew members on board. The most striking thing about flight MU5735 was the plane itself – the machine with the registration number B-1791 wore a colorful special livery showing stylized peacocks and peacock feathers and was popular with plane spotters, as numerous pictures of the colorful jet on the Internet prove. The take-off from Kunming was slightly delayed at 1:16 p.m. local time (6:16 a.m. CET), and everything went as usual for 64 minutes, the aircraft was stable for almost an hour at the cruising altitude of 29,100 feet (8869 meters). On the way.

Interestingly enough, exactly at the waypoint where the day before the same flight from Kunming to Guangzhou had started its regular descent, the routine ended abruptly on Monday. For no apparent reason, the plane went into a dive, in just one minute the Boeing lost ten thousand meters of altitude. Then something mysterious happened that the investigators have to deal with and the background to which only flight data recorders and voice recorders can provide information if they are found and are usable:

After the first dive from cruising altitude to an altitude of just 7425 feet (2263 meters), according to the data automatically transmitted by the aircraft, the dive was suddenly stopped and the aircraft climbed back to 8600 feet (2621 meters) for just ten seconds. This shows, as does the data that was further transmitted, that the aircraft must have been largely intact and also manoeuvrable at this point in time. Whether the brief interception indicates a desperate struggle between the pilots or with strangers in the cockpit to descend or climb, or a last-ditch attempt to stabilize a plane that had gotten out of control for whatever reason, the investigation can at best find out, or it will be for always remain a mystery.

However, the brief climb followed by another dive and 30 seconds of impact in the valley of a forested mountainous area near the city of Wuzhou suggests that the people on board, both in the cockpit and in the cabin, were conscious. There are two video sequences widely circulated on the Internet after the accident, one from a surveillance camera and the other from a so-called dashcam, like those used in cars in some countries. On the film recordings you can see the plane almost vertically with the nose down towards the ground almost identically.

A crater was formed on impact, the plane was torn into tiny pieces, only a few of which are on the surface, and a large forest fire broke out. It is not clear from the videos whether the Boeing was still intact or whether the elevator or tail unit were missing, but it has not yet been reported that these parts were found away from the site of the impact. And at least the fuselage seems to have been undamaged to the last, which, like the compact crash site, proves that the machine did not break apart beforehand or large parts were torn off.

On Tuesday, the accident left its mark on Chinese aviation and Boeing. Boeing’s share price fell 3.6%, twice the rate of declines so far this year. Almost three-quarters of all 11,800 scheduled domestic flights in China have been canceled, including on the Beijing-Shanghai route, typically one of the busiest routes in the world. This, however, as a precautionary measure and not because the Boeing 737-800 would be affected by a take-off ban.

Only China Eastern, the affected airline itself, the country’s second largest in terms of passengers and a member of the international Skyteam alliance with Air France/KLM and Delta Air Lines, is grounding all of its 737-800s for the time being. It operates 107 aircraft of this type itself, including the fleets of its subsidiaries, there are a total of 225. It is important to know that the accident does not affect the newer Boeing 737 MAX variant.

In 2018/2019 there were two serious crashes with a total of 346 deaths, which, according to the investigation, was due to software whose installation Boeing had concealed from the pilots. This led to almost two years of worldwide grounding of this type from March 2019 to late 2020 (in the US) and early 2021 elsewhere. In China, however, the 737 MAX has not returned to flight operations by order of the authorities, but this recently seemed imminent. However, that could now be delayed, although there is technically no connection between the current accident and the previous problems with the 737 MAX. “There is still a credibility issue for Boeing until there is more clarity about the cause,” aviation analyst Rob Spingarn told the New York Times.

The Boeing 737-800 is a more conventional airliner compared to the 737 MAX and has been in scheduled service since 1998. Since then, with over 5100 units built, it has become the most widespread model of all. According to data provider Cirium, of the approximately 25,000 commercial aircraft flying worldwide, the 737-800 accounts for 17% alone, and most of them fly in China with 1,200 examples, followed by Europe with almost a thousand. To date, the 737-800 has had a good safety record, with none of the 22 aircraft destroyed in accidents or incidents to date being due to aircraft inadequacies. China had recently developed into a model country for flight safety, also thanks to strict official supervision; the last fatal accident was recorded in 2010.