The cause of the crash was not immediately clear.
Kyrgyzstan's Emergency Situations Minister, Kubatbek Boronov, stated that it was foggy at Manas at the time of the crash, but that weather conditions were not critical.
By the afternoon of 16 January, one of the two flight recorders had been found, and the other was located later in the recovery process.
Both the flight data recorder (FDR) and cockpit voice recorder (CVR) were damaged in the crash, but investigators were still able to retrieve data from both recorders.

Deputy Prime Minister Abulgaziyev suggested that the cause may have been pilot error, noting that eleven aircraft had landed safely, despite the same weather conditions, on the previous day.
He added that the aircraft had attempted to land twice and had damaged the runway lights at one stage.
This statement was at odds with another official statement that the aircraft crashed during its first landing attempt.

The Interstate Aviation Committee (IAC or MAK) of the Commonwealth of Independent States opened a technical investigation.

The Turkish Transportation Ministry said it had sent two experts from its accident investigation board to Bishkek to assist Kyrgyz authorities.

A Boeing technical team travelled to the accident site to provide assistance at the request and under the direction of the American accident investigation body, the National Transportation Safety Board.

Many initial press responses stated that a Turkish Airlines aircraft was involved in the accident.
In response, Turkish Airlines released a statement saying that neither the aircraft nor the crew were part of the airline, calling it an "ACT Airlines accident".
Journalists were threatened by Turkish lawyers claiming reputational damage.
Nevertheless, the flight was operated under a Turkish Airlines flight number.

The preliminary investigation report found that the aircraft descended late and captured a false glideslope.
On capturing the false glide slope, the 3 auto pilots then initiated the descent of the plane in low visibility conditions.
Initially all three auto pilots were engaged (LAND 3) the false glideslope was lost 15 seconds after it was acquired and AP CAUTION and FMA FAULT 2 events were recorded meaning that the auto pilots would continue to descend the aircraft on a 3 degree slope using inertial guidance.
One autopilot disengaged (LAND 2) and the remaining auto pilots flew down to the decision height.
The crew did not acquire the required visual reference at the decision height (99 ft) and initiated a go-around 1/2 second later at 58 ft radar altitude by pressing the TOGA switches.
Given the slightly up-sloping terrain after the end of the runway, the aircraft did not have sufficient height at that point to climb out safely.

On 2 February 2020, the IAC released the final report on the accident.
The flight crew had failed to keep track of the aircraft's position on the correct glideslope and only initiated a go-around after the aircraft had deviated off course, the pre-flight briefing was insufficient, the crew did not decrease the aircraft's height so it could reach the required approach point on the navigation chart, the air traffic controllers failed to use equipment to monitor the aircraft's position, the flight crew experienced stress, and other factors.
The cause of the crash was not immediately clear. Kyrgyzstan's Emergency Situations Minister, Kubatbek Boronov, stated that it was foggy at Manas at the time of the crash, but that weather conditions were not critical. By the afternoon of 16 January, one of the two flight recorders had been found, and the other was located later in the recovery process. Both the flight data recorder (FDR) and cockpit voice recorder (CVR) were damaged in the crash, but investigators were still able to retrieve data from both recorders.
Deputy Prime Minister Abulgaziyev suggested that the cause may have been pilot error, noting that eleven aircraft had landed safely, despite the same weather conditions, on the previous day. He added that the aircraft had attempted to land twice and had damaged the runway lights at one stage. This statement was at odds with another official statement that the aircraft crashed during its first landing attempt.
The Interstate Aviation Committee (IAC or MAK) of the Commonwealth of Independent States opened a technical investigation.
The Turkish Transportation Ministry said it had sent two experts from its accident investigation board to Bishkek to assist Kyrgyz authorities.
A Boeing technical team travelled to the accident site to provide assistance at the request and under the direction of the American accident investigation body, the National Transportation Safety Board.
Many initial press responses stated that a Turkish Airlines aircraft was involved in the accident. In response, Turkish Airlines released a statement saying that neither the aircraft nor the crew were part of the airline, calling it an "ACT Airlines accident". Journalists were threatened by Turkish lawyers claiming reputational damage. Nevertheless, the flight was operated under a Turkish Airlines flight number.
The preliminary investigation report found that the aircraft descended late and captured a false glideslope. On capturing the false glide slope, the 3 auto pilots then initiated the descent of the plane in low visibility conditions. Initially all three auto pilots were engaged (LAND 3) the false glideslope was lost 15 seconds after it was acquired and AP CAUTION and FMA FAULT 2 events were recorded meaning that the auto pilots would continue to descend the aircraft on a 3 degree slope using inertial guidance. One autopilot disengaged (LAND 2) and the remaining auto pilots flew down to the decision height. The crew did not acquire the required visual reference at the decision height (99 ft) and initiated a go-around 1/2 second later at 58 ft radar altitude by pressing the TOGA switches. Given the slightly up-sloping terrain after the end of the runway, the aircraft did not have sufficient height at that point to climb out safely.
On 2 February 2020, the IAC released the final report on the accident. The flight crew had failed to keep track of the aircraft's position on the correct glideslope and only initiated a go-around after the aircraft had deviated off course, the pre-flight briefing was insufficient, the crew did not decrease the aircraft's height so it could reach the required approach point on the navigation chart, the air traffic controllers failed to use equipment to monitor the aircraft's position, the flight crew experienced stress, and other factors.
Turkish Airlines Flight 6491