Crash: Iran Aseman AT72 near Semirom

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http://avherald.com/h?article=4b511c15&opt=0

An Iran Aseman Airlines Avions de Transport Regional ATR-72-212, registration EP-ATS performing flight EP-3704 from Tehran Mehrabad to Yasuj (Iran) with 60 passengers and 6 crew, disappeared from radar near the Dena Mountain at about 09:30L (06:00Z). The aircraft was found on Feb 20th 2018 at position N30.8229 E51.6143 at an elevation of approximately 4000 meters/13120 feet. There were no survivors.

Emergency services reported fog and snowfall in the crash area hamper rescue efforts and make it impossible to land helicopters at the crash site. Rescuers are on their way to the crash site by foot.

On Feb 21st 2018 rescue and recovery personnel reached the crash site, first bodies have been recovered.

The airline confirmed the aircraft (initially reporting ATR-72-212A registration EP-ATX built in year 2000, later identifying ATR-72-212 registration EP-ATS built in 1993) has crashed in southern Iran due to "atmospheric conditions" while enroute to Yasuj with 60 passengers and 6 crew (all names were published on the airline's website). The aircraft had departed Mehrabad Airport at 08:00L (04:30Z), contact was lost about 50 minutes later. After the aircraft disappeared, helicopters were dispatched and sighted the aircraft in terrain accessible only by helicopters. Rescue forces are being dispatched on site. The airline subsequently reported no survivors were found at the crash site. The airline added, that the captain involved in the accident flight was experienced stating he had experienced the failure of the #2 engine on his aircraft and had been able to safely land the aircraft in Yasuj in 2014.

Iran's News Agency Fars identified the crashed aircraft as EP-ATS (built in 1993) based on "some source". According to Mode-S data the EP-ATS was flying about 160nm north of Semirom at 05:15Z. Iran's News Agency IRNA however reported EP-ATX based on the statement of the airline, but subsequently changed to EP-ATS.

On Feb 19th 2018 local officials reported the wreckage has been located in the range of Dangazloo (Position of village: N30.8687 E51.6483) and Noqol (Position of village: N30.8672 E51.6531), located about 11nm northnortheast of Yasuj.

Subsequently on Feb 19th 2018 the CAO (Iran's Civil Aviation Authority) denied that report stating the exact location of the wreckage has still not been determined, the last radar contact was 14nm from Yasuj. Helicopters have been dispatched again following weather improvement.

On Feb 20th 2018 Iran's Revolutionary Guards reported helicopters and unmanned aerial vehicles have sighted the wreckage 30 meters below the peak of the mountains south of Noqol (Editorial note: airway W144 leading to Yasuj passes over Nogol and Yasuj NDB, according to Google Earth the highest peak below W144 in that area rises up to about 4040 meters/13250 feet at position N30.7946 E51.6355, another peak rising up to 3900 meters/12800 feet is at position N30.8034 E51.6184, both about 7nm northeast of the aerodrome. The instrument approach chart (see below) lists the higher eastern peak at 13,984 feet/4263 meters and the other western peak at 13,819 feet/4213 meters).

On Feb 20th 2018 The Aviation Herald received verified information, that the flight had been enroute at FL210. At 05:52Z the aircraft was cleared to descend from FL210 to FL170 while tracking airway W144. At 05:53Z the aircraft was cleared to join the NDB instrument approach procedure overhead the NDB Yasuj, the crew reported 25nm from the aerodrome at 05:55Z and at 05:59z 14nm from the aerodrome. At 06:00Z the crew correctly read back QNH 1021 reported by ATC, this was the last communication from the aircraft. When tower called the aircraft at 06:04Z there was no reply anymore.

The French BEA joined the investigation led by Iran's CAO and dispatched three investigators and technical advisors to the crash site.

The Dena Mountain features more than 40 peaks above 4000 meters, the highest peak rises up to 4409 meters (14,460 feet).

The aerodrome of Yasuj is surrounded by high mountains. The AIP Iran do not publish any Standard Arrival Route, only Instrument Approach Procedures 1 (Cat A/B including ATR-72) and 2 (Cat C/D) are published together with the aerodrome chart. The IAC marks the MSA 25nm north of the aerodrome at 15,500 feet MSL.

On Oct 26th 2017 the airline had posted a photo of EP-ATS reporting that the aircraft will be restored to flying condition by qualified maintenance engineers after being out of service for seven years.

On Feb 22nd 2018 Iran's Civil Aviation Authority (CAO) reported Iran Aseman Airlines temporarily stopped operating their ATR aircraft until further notice in order to permit a comprehensive study of the causes of the crash and thus ensure safety of flights.

On Feb 23rd 2018 Iran's CAO released first information in Persian stating, that the minimum altitude along airway W144, that the aircraft was tracking on, was 17,000 feet MSL, in an emergency situation the aircraft could have descended to the minimum safe altitude of 15,500 feet spanning north of the aerodrome and around the crash site. A lot of investment had gone into Yasuj Airport, besides an NDB a DVOR/DME navigational aid has been installed at the airport as well as runway lighting permitting night operations. The aircraft carried 59 adults and one child as passengers and 6 crew (two pilots, two flight attendants, two security officers). Communication with the aircraft was lost about 85 minutes after departure from Tehran Mehrabad. Attempts to locate the aircraft via its ELT were unsuccessful. According to ATC recordings the aircraft reported overhead OBTUX waypoint on airway W144 at 09:20L (05:50Z), was cleared to descend to FL170 at 09:22L (05:52Z), was handed off to and reported on Yasuj Tower at 09:23L (05:53Z) and cleared to join the approach procedure overhead Yasuj, the aircraft descended through FL186 at 09:25L (05:55Z) and exited radar coverage due to mountaineous terrain, the crew reported being 25nm from Yasuj at 09:25L and reported 14nm DME from Yasuj at 09:29L, at 09:30L (06:00Z) the crew acknowledged the QNH transmitted by tower, at 09:32L (06:02Z) there was a transmission as if the microphone of a radio was keyed, however, no actual transmission occurred. When tower called at 09:34L (06:04Z) the aircraft did not reply anymore. The crew did not indicate any emergency or abnormal situation on board (e.g. turbulence). The aircraft was supposed to continue at FL170 until overflying the NDB, then descend to 15,000 feet and join the instrument approach procedure. The CAO reported the weather at Yasuj were very different to the reported Metars: Ambient temperature at Yasuj was between 0 and -2 degrees C (not 13 degrees C as indicated in the METARs), there were clouds between 3500 and 4500 feet with thunderstorms and overcast cloud at 9000 feet. QNH was 1021 hPa. Accident investigators are on site to recover the black boxes (FDR and CVR). The captain (62, ATPL, 17,400 hours total, 15,000 hours on type) was flight instructor within the airline. The first officer (36) had accumulated 1,846 hours total and 96 hours on type.

On Mar 3rd 2018 Iran's CAO reported that two pieces of wreckage recovered by mountain climbers according to training provided likely are the black boxes of the aircraft. Until the pieces are handed over to the specialists of the accident investigation team it is not possible to officially verify the black boxes though.

On Mar 5th 2018 Iran's CAO and the accident investigation team confirmed the pieces recovered on Mar 3rd 2018 were indeed both blackboxes, flight data and cockpit voice recorders, of EP-ATS. On Mar 6th 2018 the CAO added, that the recorders will be read out and analysed in France due to some technical issues.

On Mar 8th 2018 the CAO reported the recorders have been successfully read out in France, the data have been handed to Iran's Accident Investigation Team who will now analyse the data and prepare a report due to in due time.

On Mar 11th 2018 Iran's AIB released their preliminary report in Persian reporting that according to FDR and CVR the aircraft had been handed over to Yasuj Tower, the autopilot was set to 15,000 feet. Descending through 15,600 feet the crew activated the anti-ice systems. The aircraft levelled off at 15,000 feet on autopilot, the crew set the QNH to 1021 and maintained 15000 feet for about one minute. Then the engines were reduced to idle, the speed reduced to 200 KIAS with the angle of attack increasing, the engines get slightly accelerated. The speed continued to decrease and reached 129 KIAS (minimum maneouvering speed 132 KIAS), the pitch reaches 15 degrees nose up, the engines accelerate to 67% torque. The altitude target is set to 14,000 feet and the aircraft begins to descend at about 600fpm. The speed further reduces to 117 KIAS, a stall warning activates, the crew disengages the autopilot, the aircraft rolls 20 degrees to the left, the pitch reduces to about 9 degrees nose down. Descending through 14200 feet at 137 KIAS the autopilot gets re-engaged, the aircraft rolls right by 12 degrees, the pitch increases to 5 degrees nose down. A GPWS warning "TERRAIN AHEAD! PULL UP!" activates, the autopilot is disengaged, the GPWS warning continues for 12 seconds until impact.

The AIB continued that there was no technical malfunction of the aircraft, the engines operated in accordance to pilot inputs, all aircraft systems supplied the crew with valid data. Due to the cloud cover the crew remained unaware of the mountains ahead until 2 seconds before impact and rolled the aircraft sharply left in order to avoid the terrain.

The AIB stated that the crew should have maintained 17,000 feet in accordance with the flight plan, however, descended the aircraft to 15,000 feet followed by a target altitude of 14,000 feet on the autopilot contrary to flight rules. In addition, while the crew was permitted to conduct the flight with the weather data available at the time of departure, the latest weather information provided by Yasuj Tower indicating clouds up to 15,000 feet prohibited the approach to Yasuj according to company procedures due to cloud cover present at the aerodrome, the crew should have diverted to Shiraz or Isfahan planned as alternate aerodromes. Pilot discussions according to the CVR confirm the presence of cloud up to 15,000 feet confirming the accuracy of the weather report by Yasuj Tower. Although the aerodrome was still more than 10km away the crew appeared to be confident the area would be in visual meteorologic conditions. The AIB warns that all of this is first interpretation of first investigation results and is not to be taken as cause of the accident.