Chinese jet nearly hit speed of sound in final moments before crash

The China Eastern Airlines Corp. jet that crashed Monday was traveling at close to the speed of sound in the moments before it slammed into a hillside, according to a Bloomberg News review of flight-track data.
 

Such an impact may complicate the task for investigators because it can obliterate evidence and damage a plane’s data and voice recorders that are designed to withstand most crashes. One of the two black boxes was located Wednesday, officials in China said.
 

The Boeing Co. 737-800 was knifing through the air at more than 640 miles (966 kilometers) per hour, and at times may have exceeded 700 mph, according to data from Flightradar24, a website that tracks planes.

“The preliminary data indicate it was near the speed of sound,” said John Hansman, a Massachusetts Institute of Technology astronautics and aeronautics professor who reviewed Bloomberg’s calculation of the jet’s speed. “It was coming down steep.”

Sound travels at 761 mph at sea level but slows with altitude as air temperature goes down and is about 663 mph at 35,000 feet (10,668 meters).

Flight 5735 was flying to Guangzhou from Kunming with 132 people on board at an altitude of about 29,000 feet when it began a sudden descent, according to data transmitted by the plane and captured by Flightradar24. The jetliner was cruising at about 595 mph before the dive.
 

The speed data is consistent with videos appearing to show the jet diving at a steep angle in the moments before impact and indicates that it likely hit the ground with huge force.
 

“It was an exceedingly high-energy crash,” said Bob Mann, president of R.W. Mann & Co. consultancy, who did not participate in the speed analysis. “It looks like it literally evaporated into a crater.”

Chinese officials said Wednesday that the black box they had located was badly damaged, but didn’t say which one it was -- the cockpit voice recorder or the one that captures flight data.

Modern black-box recorders, which store data on computer chips, have a good record of survival in high-velocity crashes, said James Cash, who formerly served as the U.S. National Transportation Safety Board’s chief technical adviser for recorders.

The circuit boards storing the data often break loose from the recorder’s protective exterior. But data can usually be extracted even if they’re damaged, Cash said before the black box was found.

“I would suspect it would be O.K.,” he said.

No Beacon Activated

The search for the remaining one won’t be aided by a beacon or “ping” from the devices because they are only activated underwater. The two recorders on the China Eastern 737-800 were supplied by the aerospace division of Honeywell International Inc. and installed on the plane when it was new, according to company spokesman Adam Kress.
 

Crash investigators have over decades perfected the examination of wreckage in search of clues, but some impacts can obliterate evidence. The crash of an Ethiopian Airlines 737 Max in 2019 was traced back to a sensor on the plane’s nose, but the sensor was never found after the jet hit the ground at a high speed, according to a preliminary report from that nation.

Accident investigators should be able to find more precise speed data from the jet’s flight recorder. If it isn’t available for some reason, aerodynamic experts can perform extensive analysis to more closely estimate speed.

Flightradar24’s data includes the jet’s speed, but it’s measured horizontally across the ground. Bloomberg’s computations give a rough idea of how fast it was flying through the air by taking into account its horizontal speed over the ground as well as how fast it was descending.  

The speed estimates were based on how fast the jet traveled between two points and didn’t take into account wind direction or other atmospheric conditions. The Bloomberg review was conservative and actual speeds may be higher. While unverified videos showed the plane diving at a steep angle near the ground, it wasn’t clear how fast it was traveling at impact. The last data transmission captured by Flightradar24 occurred at about 3,200 feet altitude.

About 40 seconds before the last transmission, the jet stopped descending and briefly climbed before resuming the dive. During these later stages of the flight, it slowed somewhat, according to the preliminary review.
 

It was still flying far faster than normal. Typically, jets don’t go above 288 mph at altitudes below 10,000 feet. The China Eastern jet was traveling at roughly 470 mph or more at those altitudes, according to Flightradar24 data.