Many have probably heard about China Eastern Airlines Flight MU5735 that crashed near Wuzhou, China on March 21, 2022. Something caused the plane to enter a steep dive while the flight was straight and level at its cruising altitude and impact the ground minutes later. Airplane accidents are extremely rare events, and it is extremely rare for an accident to happen in this way. This post reports what is currently known about the accident and discusses possible causes.

Flgihtradar24 has disseminated much information about the flight. Flightradar24 is a Swedish company that continually collects Automatic Dependent Surveillance–Broadcast (ADS–B) data in real time about airline flights world wide. ADS-B has replaced radar as the primary tool used by air traffic control tool for tracking commercial airliners.  

China Eastern Flight MU5735

China Eastern Airlines (MU) flight 5735 was scheduled to depart Kunming at 13:10 local time (05:10 UTC) and arrive in Guangzhou at 15:05 local time (07:05 UTC). (UTC refers to Universal Coordinated Time which was previously known as Greenwich Mean Time.) The flight was operated by a Boeing 737-800. This model is different than the 737MAX and is not equipped with the MCAS system that was determined to be the primary cause of two 737MAX crashes a couple of years ago.

The flight crew was very experienced. The captain had almost 7,000 flying hours, while the first officer had more than 31,000 hours of experience. A third pilot was on board as an observer and had 556 flying hours.

MU5735 departed Kunming at 05:16 UTC and reached a cruising altitude of 29,100′ 11 minutes later. The flight continued normally until 06:20 UTC when the aircraft began a rapid descent to 7425 ft amsl (above mean sea level) before recovering to 8600′ amsl. At which point the aircraft entered another steep dive. The last ADS-B message was at 06:22:35 UTC at an altitude of 3225′ amsl.

Flightradar24 prepared this graph depicting the final 150 seconds of ADS-B data on altitude, ground speed and vertical speed.

MU5735-final-150-seconds-Altitude-Speed-Vertical-Rate-Chart

This information is illustrated below.

MU5735-Descent-Profile-1920x1318

After a normal flight, MU5735 suddenly and rapidly descended and crashed within a span of about two minutes.

Possible Causes

The cause is undetermined at this time. There are, however, clues about what may or may not have happened. I’m not an airline pilot. This analysis relies on knowledge of other airline accidents and my private pilot training and experience.

Aerodynamic Stall

The airspeed (speed of the plane relative to the air through which it is moving) has not been publicly available although the airspeed can be presumed to have been relatively constant because of the constant groundspeed (the horizontal speed of an aircraft relative to the Earth’s surface). If airspeed was constant, that rules out loss of lift from an aerodynamic stall as the cause of the initial dive.

It is possible that the plane could have lost enough airspeed during the recovery from the initial dive at about 8500′ amsl and 5,000′ agl (above ground level) to enter a stall. Pulling the nose up to stop the initial rapid descent and establish a positive rate of climb would certainly reduce airspeed. A stall might explain the second rapid descent. If the aircraft stalled at an altitude only 5,000′ above the terrain, recovery would be more challenging but not impossible by any means.

Engine Failure

Engine failure is an unlikely cause of the crash even in the unlikely event of a simultaneous double engine failure. From 29,000′ the pilots could have maintained a slight nose-down attitude and glided for a great distance. Engine failure would not explain the second dive either.

Inflight Break Up

In extremely rare cases, planes have broken apart in midair for various reasons including metal fatigue. A strip of metal that may have come from the plane was found 10 km from the crash site. The final descent and impact was recorded on a security camera at a nearby industrial site. The plane appears to be intact.

Elevator Malfunction

Steep dives might indicate a problem with the elevator, the flight-control surface on the tail that raises and and lowers the nose. If a problem with the elevator or its trim control caused the first dive, that problem must have been fixed, at least temporarily, because the plane pulled out of the initial dive at about 7,500′ AMSL.

Intentional Act

A pilot intentionally crashing a plane has happened only a handful of times in the history of commercial aviation. The most recent known example is Germanwings Flight 9525 in 2015 where a pilot crashed an Airbus A320 into the French Alps. At this point, an intentional act by the pilots or someone else on board cannot be ruled out.

Radio communication with the aircraft was normal during the flight. But there were no radio calls from the aircraft, and the pilots did not respond to calls from air traffic control during the incident. The lack of communication from the flight deck might be evidence of an intentional act by someone.

The possibility of sabotage of equipment or systems can’t be ruled out either at this point.

FOXZfKEXoAM2YEJ

Status of the Investigation

Information from the flight data recorder (FDR) and cockpit voice recorder (CVR) will be crucial in determining what caused this crash. The CVR has been recovered. It has been taken to Beijing where it is being examined. The FDR should be found soon. The information from the FDR will shed light on any mechanical problems the aircraft experienced.

Chinese investigators have invited representatives from the U.S. National Transportation Safety Board (NTSB) to join the investigation because the plane was manufactured in the U.S. It may take them a couple of weeks to take part because of Chinese quarantine requirements.

Participation of the NTSB may alleviate concerns over transparency in the investigation. In a few instances, countries have gone to great lengths to avoid assigning any blame for crashes to their own pilots.

Final Thoughts

Airline travel is the safest form of travel and commercial airlines are the safest form of air travel. This commercial airline accident is the first one in China since 2010. The 737-800 is one of the most widely used airliners and has compiled an outstanding safety record.

China Eastern is a decent airline although it has some customer service problems. I’ve flown on China Eastern 737-800s several times. I’d do so again without hesitation except I’m now reluctant to visit or transit through the People’s Republic for reason unrelated to aviation safety.

If there was an intentional act by anyone on board, that should be identified by the CVR rather quickly. Otherwise, identifying the cause may take quite some time. In either case, the release of an official accident report will take months.

Do you have thoughts or questions about MU5735? Don’t let this unfortunate incident deter your travel plans.