Created Sunday, Jul 12th 2020 16:50Z, last updated Monday, Aug 24th 2020 16:18Z
On Aug 24th 2020 Iran's AIB released their FDR/CVR readout report in English and Persian reporting - differently to Iran's CAA - that at 02:44:56Z (06:14:56L) the first missile detonated causing the immediate failure of the FDR, the CVR however recorded the sound of the explosion and continued to record until 02:45:15Z. The investigator in charge states: "The post-detonation sounds show that all the three crew members inside the cockpit had been controlling the situation without any indication of injury/damage to their health. Over the short time of post-detonation recording, according to the instructor pilot, the aircraft engines had still been running, and the flight crew had decided to use the APU. As yet, there exists no voice or sign revealing the passenger cabin's conditions in the recorded data and audios. The information obtained from the flight recorders read-out substantiates the events stated on the Factual Report released by the accident investigation team in July 2020. The information extracted from the flight recorders and other available information indicate that the activation of the first missile fuse caused considerable damage to the aircraft. The detonation and impact of the objects thrown out from that led to the immediate failure of FDR and after 19 seconds, the CVR."
On Aug 23rd 2020 Iran's Civil Aviation Authority reported both FDR and CVR were read out without any technical difficulties. All aircraft systems were working normally and the situation on board was normal until the explosion of the first missile at 06:14:56L (02:44:56Z). Following the explosion one pilot can be heard porivding instructions to the other pilot and advising that both engines were running. Both FDR and CVR continued to record for 19 seconds after the first explosion until both simultaneously failed. Due to the failure 19 seconds after the first explosion the effects of the second explosion 25 seconds after the first can not be assessed from the recordings of the black boxes.
On Jul 23rd 2020 the BEA announced that analysis work on CVR and FDR data with all stakeholders (ICAO, AIB Iran, NBAAI, SHK, TSB, NTSB, AAIB, Boeing, Safran Engines, UIA) is finished.
On Jul 20th 2020 the BEA reported Iran's AAIB Team with the FDR and CVR have arrived at the BEA headquarters, work to download and decode the data has begun.
In the early afternoon of Jul 20th 2020 the BEA reported the CVR was successfully downloaded including the data of the accident flight. The data have been transferred to Iran's AAIB.
In the late evening of Jul 20th 2020 the BEA reported the FDR was successfully downloaded, too, including the data of the accident flight. The data have been transferred to Iran's AAIB, too.
On Jul 12th 2020 Iran's AIB released another
updated interim report (in both Persian and English, English version follows after 17 pages of Persian) stating that at 00:30Z Iran's Air Defense changed their alert levels and instructed the civil sector that only flights cleared by the defense network could be permitted to start up. At 02:21Z PS-752 requested clearance to start their engines, ATC forwarded the request to Air Defense at 02:22Z, Air Defense cleared the flight at 02:23Z. At 02:40:20Z the flight was cleared for takeoff from Imam Khomeini Airport. The report writes: "The flight proceeded towards the flight route at the planned altitude and trajectory."
The report then highlights (with a red Attention Triangle):
After the relocation of one of the air defense units of Tehran, clearly causing a change in its heading, a failure occurred due to a human error in following the procedure of system north alignment. As a result, a 107-degree error was induced in the system. As such, while the PS752 aircraft was flying, the direction of objects and targets detected by this system was being observed with an increase of 107 degrees by the operator. Such a functional failure initiated a hazard chain, which, of course, could be controlled providing other planned measures are implemented.
At 02:43:56, the air defense unit operator detected a target at his 250-degree azimuth, flying on a 52-degree course. At the same time, after takeoff, the PS 752 had been flying towards the defense system from a 143-degree azimuth. The aircraft was passing a 309-degree course.
At 02:44:21, the operator notified the specifications of the detected target to the Coordination Center over the communication network (note paragraph 10 on the communication status). The target was, in fact, the very PS 752 flight departing from IKA, detected by the system as a target approaching Tehran from approximately the southwest.
The recorded information indicates that the mentioned defense system's notification was not communicated successfully. Another link in the chain of events was formed at this point.
The system operator began analyzing the observable information and categorized the detected target as a threat. Although the likelihood of identifying the target for a threat was considerably raised due to his lack of awareness of the 107-degree error, yet still if at this point he had identified the target as a passenger aircraft, the missile would not have been launched. The wrong identification is another link in the chain of events.
At 02:44:41, without receiving any response from the Coordination Center, the air defense unit operator fired a missile at the threatening target he had detected. Under the applicable procedures, if the defense system operator cannot establish communication with the Coordination Center and does not receive the fire command, they are not authorized to fire. This measure had been planned as another error prevention layer, which was not implemented either. The fourth link leading to the firing of the missile was now formed.
At the time of firing the first missile, the aircraft was flying at a normal altitude and trajectory. The aircraft ATC transponder and ADS-B5 signals were received properly.
The missile radio fuse was activated when the aircraft had reached the last position recorded by the dependent surveillance systems. The activation occurred at 02:44:59.
At 02:44:58, the last information received from the aircraft included the Secondary Surveillance Radar (SSR) transponder and Automatic Dependent Surveillance-Broadcast (ADS-B), after which the receiving of such signals was terminated. This time corresponds to the first missile radio fuse activation. From then on, the aircraft position was only being recorded by the Primary Surveillance Radar (PSR).
After the first missile radio fuse was activated, the air defense unit radar still locked on the target, and the defense system kept detecting and tracking it.
By observing the continuity of trajectory of detected target, the second missile was fired at the aircraft by the operator of defense system at 02:45:11.
At 02:45:24, the last communication between the missile and the defense system was recorded in a place close to the aircraft route. After that, the defense system showed a message indicating the strike had failed, with the aircraft clearing from the radar lock-on after some time.
The aircraft turned to the right. Due to the radio communication disconnection, there is no information on the aircraft altitude during the time when it was being detected by the Primary Surveillance Radar.
The evidence shows that at about 02:46:11, a fire broke out on the aircraft, which was intensifying.
At 02:48:23, the aircraft crashed into a playground in Khalajabad near Shahedshahr area. An explosion occurred the moment the aircraft impacted the ground. The aircraft then kept hitting the ground and bouncing on a route towards the airport, making the aircraft pieces, victims' properties, objects and body remains disintegrate completely in a vast area near a residential complex, recreational and sports park, gardens and the surrounding agricultural land.
The aircraft was carrying 176 people on board, nine of whom were the flight crews and the rest passengers. All people on board had already died when the accident site was identified.
The effects produced by the explosives on the aircraft fuselage were analyzed, and it was found that they have similarities to the expected ones of the detonation of the defense system warhead.
Editorial note: Using the position of the aircraft at its correct position at the time of detection, azimuth 143 degrees to the radar site, as well as the false detection position at 250 degrees azimuth, the position of the radar site (and probably the launch site of the missiles) was at position N35.5750 E50.8856.
