Recorded conversations by pilots on a cargo jet carrying packages for Amazon.com Inc. that crashed last month near Houston reveal they began losing control of the aircraft about 18 seconds before it slammed into a shallow bay, investigators said Tuesday.

The communications captured on the cockpit sound recorder were “consistent with a loss of control of the aircraft,” according to a press release issued by the National Transportation Safety Board. The NTSB recovered the crash-proof cockpit recorder and another black box storing flight data in recent days and brought them to its lab in Washington for analysis.

The press release, offering a first glimpse of what happened on the Boeing Co. 767-300 as it was preparing to land at Houston’s George Bush Intercontinental Airport Feb. 23, still doesn’t explain its mysterious, abrupt dive. The second recorder contained detailed data from the accident flight as well as 16 previous ones, but none of its contents were revealed in the NTSB statement.

Atlas Air Flight 3591 dove roughly 6,000 feet (1,829 meters) and plunged into a shallow bay as it was descending and preparing to move around a line of storms ahead. The impact shattered the plane and killed all three aboard: two Atlas pilots and one from a regional airline who was catching a ride. There was no emergency radio call from the cockpit.

Atlas was one of three cargo carriers flying a fleet of 50 aircraft for Amazon, according to a press release from the online retailer in December. Atlas is owned by Atlas Air Worldwide Holdings Inc.

A video recorded from a jail about a mile from the crash showed the plane’s final five seconds before it smashed into the water, NTSB Chairman Robert Sumwalt said in a briefing Feb. 24. The plane was in “a steep descent, steep nose-down attitude” and there was no evidence the pilots tried to “turn or pull up at the last moments,” Sumwalt said.

A separate video from a nearby school showed the plane apparently diving until it disappeared in a cloud bank, according to the Houston Chronicle.

The cockpit recorder is about two hours long, but the audio quality is “poor,” the NTSB said. “There are times during the recording when the content of crew discussion is difficult to determine,” the press release said. “At other times the content can be determined using advanced audio filtering.”

The NTSB is convening a group of experts to evaluate the recorder’s contents and to produce a transcript, the agency said in its release. “It will be a time-consuming process to complete the transcript,” the agency said.

The plane was at an altitude of about 6,200 feet at the time pilots first discussed the unspecified control issue, according to a flight plot provided by tracker FlightRadar24. Around that time, it climbed slightly for a few seconds, then began to drop, according to the website.

It went from 5,850 to 1,325 feet, the last position captured by the website, in about nine seconds, which is many times faster than a normal descent rate.

Pilots were talking to air-traffic controllers and were being guided to the airport, the NTSB said. The normal route to the airport was being altered so they could fly around thunderstorms, according to a recording released by the website LiveATC.net.

The plane’s data recorder captured about 350 parameters, which typically include information on the health of the engines and other aircraft systems, details of the route and speed, and indications of levers and switches activated in the cockpit. Investigators are in the process of validating the data and plan to release more information in a few days.

The 767 family of jetliners, which were introduced in 1982, has a solid safety record. There had been only two fatal crashes on the plane through 2017, according to Boeing’s annual aircraft safety summary.

Related:

Copyright 2020 Bloomberg.