Iran Aseman AT72 near Semirom on Feb 18th 2018, impacted terrain

Last Update: May 24, 2021 / 14:56:41 GMT/Zulu time

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Incident Facts

Date of incident
Feb 18, 2018


Flight number

Yasuj, Iran

Aircraft Registration

Aircraft Type
ATR ATR-72-200

ICAO Type Designator

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 N30.8238 E51.6158 at an elevation between 13,185 feet and 13,054 feet MSL (top of the mountain 13,412 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.

On Feb 18th 2019 Iran's AIB released their report labelled interim report (in English!) (Editorial note: the report seems to be consistent with a final report as it includes full analysis and conclusions, however, still has the status of an interim report though being close to the release of the final report, the AIB is currently waiting for comments on the already sent out draft final report) concluding the probable causes of the crash were:

The accident was happened due to many chains of considered causes but the “Human Factor” had main roll for the conclusion of the scenario. The Cockpit Crew action which has caused dangerous conditions for the flight is considered as main cause. Based on provided evidences, the errors of cockpit crew were as follows:

- Continuing to the Yasouj airport for landing against Operation manual of the Company, due to low altitude ceiling of the cloud and related cloud mass. They should divert to alternate airport.

- Descending to unauthorized altitude below minimum of the route and MSA

- Lack of enough CRM during flight

- Failure to complete the stall recovery (flap setting, max RPM).

- Inappropriate use of Autopilot after Stall condition

- Inadequate anticipation for bad weather based on OM (Clouds, Turbulence, and Icing ...)

- Quick action to switch off anti-ice system and AOA

- Failure to follow the Check lists and standard call out by both pilots

Contributing Factors:

The contributive factors to this accident include but are not limited to the following:

- the airline was not capable to detect systematic defectives about :
* effectiveness of crew training about Meteorology, OM, SOP, ...
* enough operational supervision on pilot behaviors
- The lack of SIGMET about Mountain Wave or Severe Mountain wave

- Unclear procedure for stall recovery in FCOM

- Lack of warning in aircraft manuals by manufacturer for flight crew awareness about mountain wave.

- Lack of APM System to alert crew about performance degradation

Other Deficiencies and Short Comes:

In the process of the accident investigation, some detailed deficiencies and short comes were found and should be considered as latent conditions by related authorities:

- AD accomplishment and related monitoring

- Sanction on aviation industries and effect on Flight safety

- Non-standard communication between ATC and crew

- Unclear definition of the Fully Qualified Pilot and qualified copilot in Aircrew regulation.

- weather forecast (TAF) in the airports based on annex 3

- procedure in the Civil Aviation Organization for approving alternative method of compliance for aircraft AD,s

- Search and rescue Coordination with local authorities for aviation accidents.

- time setting of aircraft flight data recording(FDR) either by technician or pilots

The AIB reported that the DME in association with Yasuj DVOR was not received (in accordance with NOTAMs). Tower instructed the crew to use the DME associated with Yasuj NDB instead. The captain (62, ATPL, 17,926 hours total, 12,519 hours on type) was also training pilot of the company and CAO examiner, he had flown to Yasuj twice in the last three months. The captain was pilot monitoring. The first officer (36, CPL, 1,880 hours total, 197 hours on type) was pilot flying.

The AIB reported that in cooperation with the French BEA an engineering performance simulation was done. The result:

BEA reported that there was not any performance degradation by ice formation on the wing and aircraft kinetic energy was based on the inputted engine power and aerodynamics characters of flight path accordingly before stall warning. The simulation was based on the takeoff weight and CG data from the load and trim sheet. The SAT at the time of aircraft descending from FL170 to FL150, the simulation revealed a good consistency of aircraft performance motion during the decent for approach Yasouj aerodrome. So the aircraft behavior was due to aerodynamic effect (down draft) of mountain wave.

The AIB analysed:

Based on factual information, the aircraft was flying on the cloud with icing condition and the pilot tried to fly in unauthorized altitude to segregate from the clouds/icing condition and reached unsafe altitude from the mountains. The flight was continued by cutting off the anti-ice/De-ice systems. The flight encountered to mountain wave phenomenon, and tendency to increase altitude of the aircraft was due to updraft, followed by air motion down draft at the area of aircraft near to the top of the mountain. Aircraft experienced low energy flight and low speed, finally caused to approach stall condition.

The pilots couldn't be well awarded about the existing critical conditions for the aircraft decent flight profile which may cause deterioration of aerodynamic loads and spoil the correct aircraft flight configuration. At the end of flight, pilots tried to recover kinetic energy of the aircraft in order to control the flight but the aircraft performance couldn’t compensate high rate descend of flight.

With respect to the FDR the AIB analysed:

Before reaching Altitude 15000ft, the altimeter setting was changed to QNH 1021. The aircraft leveled at 15,000 ft. During one minute, the IAS was around 200 kt with engine power levers retarded to minimum flight idle (engine torque around 10%) and aircraft pitch down attitude, mainly around -5°. Such an airplane behavior during an altitude hold (pitch down, no power requested and stable speed) was consistent with an airplane flying in updraft wind.

From 09:29:28 to 09:30:45, the vertical wind direction changed. It gradually moved from an updraft wind to a downdraft wind. The aircraft pitch started to increase and the IAS decreased, drag increased accordingly. Then power levers were progressively pushed towards the notch, with engine torque increasing. Based on CVR, the pilot told “wow” which might be due to understanding low speed and focused on putting off a system which leaded to warning prevention. They might refer to AoA after disconnecting LEV II anti-ice system.

At 09:30:44, 25s after the power levers were set to the notch, the IAS reached 129 kt (the minimum low bank manoeuver speed in normal conditions for the given aircraft weight (VmLBO) was 132 kt), the pitch attitude was around +15°, both engine torque were at 67%. The aircraft then started to descend towards the new selected altitude of 14,000 ft and began to descend.

At 09:31:14, the IAS reached a minimum of 118 kt. The angle of attack of the aircraft increased and One second after the stall warning threshold was reached; triggering the stick shaker quit immediately follows by stick pusher activation. Due to stick pusher activation, the pitch attitude decreased. Due to the stall warning, the AP disengaged .the aileron went to position where the hinge moment were balanced. That position induced a limited roll rate to the left until reached 20° left wing down. A pitch down input up the captain was recorded at 09:31:20 and the pitch attitude decreased down to -9°. The crew did not stall recovery procedure completely.

- Based on SOP, the crew should push down the nose until out of stall, and get 15 degree flaps, roll to wings level and increase power as needed. The crew did not set flap however the first officer asked pilot about flap setting. MCT power was previously set on the PWR MGT selector

- Based to on date QRH, at this situation crew should push control wheel firmly, get 15 degree flap, set MCT power, CL to max RPM, PL to notch and then notify the ATC. This procedure is different from SOP.

- There is no any reference in new QRH of FCOM with version 2018 or SOP that the crew is authorized to push power lever up to RAMP or Wall for stall recovery to increase power. Also if crew does not set CL to MAX, propeller will not reach to MAX RPM.

At 09:31:23, at 14,200 ft and IAS 137 kt, the autopilot was re-engaged again and took the control of the pitch and roll attitude. Pitch increased up to -5° and aircraft rolled right to 12°. The pitch increased and reached -4°, while the airplane rolled to the right, banking 12° right wing down.

During the last A/P engagement, the A/P had not the authority to capture the requested altitude without first overshooting it due to the initial conditions: engagement at less than 500 ft from the target altitude, at a vertical speed of more than 4,000 ft/min. The BEA analysis of the recorded parameters validated the autopilot behavior. The non- capture of the selected altitude of 14,000 ft was only due to the initial condition of the A/P engagement: close to the selected altitude with a high initial vertical speed to allow the capture of the selected altitude without first overshooting it.

From 09:31:24, EGPWS alerts triggered (Terrain ahead caution, then terrain ahead Pull Up warning).

At 09:31:32, pilot tried to pull up the aircraft then 2s latter the autopilot disengaged while the EGPWS alerts continued until the end of the recording.

The last relevant part of the CVR Transkript produced by Iran's AIB:
09h22min30 ACC: Descent to FL 170, radar service terminated, continue to destination
09h22min45 Horn
09h23min04 Position 35 mile to yasouj descending 170
09h23min48 Weather condition request to ATC
09h23min54 TWR: Final for RWY 31 is clear; if you make NDB approach, you can see the RWY
09h24min07 Captain: We are coming overhead FL 150 and we hope to get out for clouds on FL 145 to 150
09h24min55 Captain to ATC: Yasouj DME is not working
09h25min06 Captain to ATC: I have the DVOR but I have not the DME 09h25min19 TWR: Use the DME from the NDB because the DME from the DVOR is not working
09h25min37 Captain to ATC: We are now 25 NM 09h25min48 TWR:Left base of the RWY is getting clear by the moving of the clouds
09h26min45 C-Chord (Altitude Alert warning)
09h27min17 Single chime (Master Caution warning) ) captain: Level 3 on
09h27min29 Captain: We don't have the Transition Level information
09h27min34 Captain to ATC: Transition level request
09h27min37 First Officer: It should be FL 150
09h27min43 TWR: 170 Captain
09h27min48 Captain to ATC: Yes, thank you
09h27min49 C-Chord (Altitude Alert warning)
09h28min08 FO: what a bad weather!
09h28min08 C-Chord (Altitude Alert warning)
09h29min03 TWR: IRC3704 your position?
09h29min10 Captain to ATC: Position 14 NM, not received the DME
09h29min15 TWR: Be advised left down wind and left base of the RWY 31 are almost cleared of clouds
09h29min31 First Officer: Left down wind and Left base – We should go overhead
09h29min38 Captain: We can't go now – It is behind these clouds.
09h30min10 Captain to ATC: Acknowledge QNH 1021
09h30min27 Captain: Why?! (Surprise/Fear)
09h30min32 Captain: We ----- cut off this component to be silent.
09h30min34 First Officer: Can we get flap? – Could we descend?
09h30min46 Captain: set it on FL140
09h30min59 C-Chord (Altitude Alert)
09h31min15 Stall Warning + Stick Shaker 09h31min16 Cavalry Charge (Autopilot disconnection warning)
09h31min16 First Officer: May I set the flaps?
09h31min20 Cavalry Charge (Autopilot disconnection warning)
09h31min21 Captain: please set Autopilot
09h31min25 EGPWS Warning: Terrain ahead
09h31min26 EGPWS Warning: Terrain ahead
09h31min28 EGPWS Warning: Terrain ahead
09h31min29 EGPWS Warning: Pull up
09h31min30 EGPWS Warning: Terrain ahead
09h31min31 EGPWS Warning: Pull up
09h31min33 EGPWS Warning: Terrain ahead
09h31min34 EGPWS Warning: Pull up
09h31min34 Cavalry Charge (Autopilot disconnection warning)
09h31min36 EGPWS Warning: Terrain, Terrain
09h31min37 EGPWS Warning: Pull up
09h31min40 EGPWS Warning: Pull up
09h31min41 Continuous Repetitive Chime (CRC, Master Warning)
09h31min42 EGPWS Warning: Pull up
09h31min42 End of the flight
09h31min42 End of recordings

On May 24th 2021 the final report was noticed on Iran's CAO Website, which in essence is identical to the previous interim report of Feb 18th 2019 except for an addition by BEA comments and slightly reworded findings.

Metars Yasuj:
OISY 180630Z 14006KT 9999 FEW035CB SCT040 OVC090 15/M02 Q1021=
OISY 180600Z 13004KT 9999 FEW035CB SCT040 OVC090 13/M00 Q1021=
OISY 180530Z 09004KT 9999 FEW035CB SCT040 OVC090 14/M01 Q1022=
OISY 180500Z 00000KT 9999 SCT040 OVC090 11/M00 Q1021=
OISY 180430Z 08006KT 9999 SCT040 SCT090 10/M01 Q1021=
OISY 180400Z 14006KT 9999 FEW040 BKN090 06/00 Q1022=
OISY 180300Z 00000KT 9999 FEW040 BKN090 06/M00 Q1022=
OISY 180200Z 16004KT 9999 FEW040 SCT090 07/M00 Q1022=
OISY 180100Z 10004KT 9999 FEW040 SCT090 06/00 Q1022=

Wreckage found on Feb 20th 2018 (Photos: APA/Mohammed Khademosheikh/Mizan News Agency):

Infrared Satellite SEVIRI IODC Image Feb 18th 2018 06:00Z (Graphics: AVH/Meteosat):

Map view overhead Noqol at 7000 meters/FL230 looking towards crash site and Yazuj (Graphics: AVH/Google Earth):

Detail Map (Graphics: AVH/Google Earth):

Area Map (Graphics: AVH/Google Earth):

Map (Graphics: AVH/Google Earth):

Excerpt of Enroute Chart around Yasuj (Graphics: AIP Iran):

Instrument Approach Chart 1 Yasuj (Graphics: AIP Iran):
Incident Facts

Date of incident
Feb 18, 2018


Flight number

Yasuj, Iran

Aircraft Registration

Aircraft Type
ATR ATR-72-200

ICAO Type Designator

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