Iran Aseman Airlines Flight 3704 was a scheduled Iranian domestic passenger flight from Iranian capital

Tehran Tehran (; fa, تهران ) is the largest city in Tehran Province and the capital of Iran. With a population of around 9 million in the city and around 16 million in the larger metropolitan area of Greater Tehran, Tehran is the most popul ...

Yasuj Yasuj ( fa, ; also romanized as Yāsūj, Yasooj, and Yesūj; Luri language, Luri: ''Jasuc'' or ''Jasyç'') is a city and capital of Kohgiluyeh and Boyer-Ahmad Province, Iran. At the 2006 census, its population was 96,786, in 20,297 families. Ya ...

in southwest Iran. On 18 February 2018, during its approach to Yasuj, the aircraft serving the flight, an ATR 72-212 operated by Iran Aseman Airlines, crashed into Mount Dena in the

Zagros Mountains The Zagros Mountains ( ar, جبال زاغروس, translit=Jibal Zaghrus; fa, کوه‌های زاگرس, Kuh hā-ye Zāgros; ku, چیاکانی زاگرۆس, translit=Çiyakani Zagros; Turkish: ''Zagros Dağları''; Luri: ''Kuh hā-ye Zāgr ...

near Noqol village in

Semirom Semirom ( fa, سميرم, also Romanized as Semīrom, Samirum, and Sīmrom) is a city and capital of Semirom County, Isfahan Province, Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country loc ...

county, Isfahan Province. All 60 passengers and 6 crew members on board were killed. According to the interim report, which was published on 18 February 2019 by the Iranian Civil Aviation Organization (CAO), the accident was caused by multiple factors, with pilot error considered as the main cause. The investigation showed that the crew decided to continue to Yasuj despite deteriorating weather conditions in the area. During its approach, the crew elected to descend below the minimum altitude. The resulting bad weather caused the aircraft to stall. The crew failed to recover the aircraft from the stall and the aircraft crashed onto the mountain. The crash highlighted the danger of

mountain wave In meteorology, lee waves are atmospheric stationary waves. The most common form is mountain waves, which are atmospheric internal gravity waves. These were discovered in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, above ...

and the aviation industry's lack of awareness of the issue. The Iranian CAO published several recommendations to ICAO and the

European Aviation Safety Agency The European Union Aviation Safety Agency (EASA) is an agency of the European Union (EU) with responsibility for civil aviation safety. It carries out certification, regulation and standardisation and also performs investigation and monito ...

to address the hazard that a mountain wave may pose to the safety of a flight. Subsequently, the crash also led to changes of the weather training programs for airliners in Iran.

Aircraft

The aircraft involved was an

ATR 72 The ATR 72 is a twin-engine turboprop, short-haul regional airliner developed and produced in France and Italy by aircraft manufacturer ATR (french: Avions de transport régional or it, Aerei da Trasporto Regionale), a joint venture formed ...

-212 with

MSN MSN (meaning Microsoft Network) is a web portal and related collection of Internet services and apps for Windows and mobile devices, provided by Microsoft and launched on August 24, 1995, alongside the release of Windows 95. The Microsoft Net ...

391. It was registered EP-ATS and was delivered to Iran Aseman Airlines in 1993. No serious incidents were recorded during the aircraft's 24 years of service in the airline. An Iranian source reported that the aircraft had recently resumed operations after being out of service for seven years due to a lack of spare parts and that it had technical problems during a flight some weeks before the crash. It was claimed that an Instagram post from Iran Aseman two months prior to the crash, that announced the aircraft was back in service, had been deleted after it crashed. At the time of the accident, Iran Aseman had six ATR aircraft in its fleet, three of which were in operation.

Passengers and crew

It was initially reported that 59 passengers and six crew members were presumed to be on board. It was later revealed that there were 60 passengers and six crew members aboard. The flight manifest was consisted of 65 adults and 1 child. There were 60 passengers, 2 security guards, 2 flight attendants and 2 flight crew members. The pilot of the flight was identified as 62-year old Hojatollah Foladi. He had accumulated a total flying hours of more than 17,000 hours, of which 12,000 hours were on the type. The pilot also had experience of flying in India from 2002 to 2007, before returning to Iran Aseman Airlines. At least 2 flights to Yasuj had been performed 3 months prior to the accident. His flying certificate was deemed as valid. The pilot not flying was identified as 36-year old First Officer Khevah Khalili with a total flying hours of approximately 1,800 flying hours, including 197 hours on the type.

Accident

The

aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engine ...

was operating a domestic scheduled passenger flight from Iranian capital Tehran Mehrabad International Airport to Yasuj Airport in

, the capital of Kohgiluyeh and Boyer-Ahmad Province in southwest Iran. The flight was supposed to take about 50 minutes. It was operated by Iran Aseman Airlines, the third largest airline in Iran. It took off from Tehran with 60 passengers and 6 crew members on 18 February 2018 at about 04:35 UTC. At 05:49 UTC, as Flight 3704 approached Yasuj, the flight crew asked the meteorological information in Yasuj. Yasuj Tower later informed Flight 3704 about the weather condition and mentioned that the final approach path was clear. The flight later was cleared to descent to FL170 by Tehran and was handed over to Yasuj on 05:53 UTC. The crew stated that they would continue the approach with FL150. At 05:55, the crew reported that they were 25 miles from the destination airport. Yasuj Tower then told the pilot about the updated condition in Yasuj, stating that clouds were slowly moving to the south. Four minutes later, Yasuj asked the flight again and the crew responded that they failed to receive the signal of Distance Measuring Equipment (DME) from their navigational device. The crew then checked about the weather condition in the area again. At 06:04 UTC, Yasuj Tower lost communication contact with Flight 3704. Attempts had been made to re-establish communication with the aircraft but failed. According to flight tracking website Flightradar24, the last signal from the aircraft was received just before 05:56 UTC, descending from an altitude of .

Search

Locals reported that they had heard the aircraft hit the mountain. Iranian authorities in neighboring Shiraz and Isfahan province had deployed two of their helicopters to the crash site. A total of 12 search and rescue teams had been dispatched to Mount Dena, but due to foggy conditions, rescue helicopters could not reach the crash site in the

. Mount Dena, the location of the crash site, is actually a mountain range within the Zagros Mountains; it is long with several peaks, the highest of which is above sea level. Spokesman from Iran Aseman Airlines initially stated that all 66 passengers and crews on board had been killed in the accident. However, this statement was later retracted by the airline and the airline later issued a statement saying that it could not "accurately and definitely confirm" that everyone had died in the crash. In response to the crash, crisis centres were set up in

, Isfahan, Fars and Yasuj. Weather conditions at the crash site, including snow and strong winds, were hampering search and rescue services. The Red Crescent Society announced that a drone would be flown to the area due to the severe weather condition which prevented helicopters to reach the crash site. Search and rescue team announced on 19 February that at least 5 helicopters had been prepared for the search operation. Troops with search dogs were deployed to hike the mountain and to search the area on foot. Search and rescue operation via air was stopped for the second time due to bad weather conditions. Reports that the wreckage had been found at an elevation of 11,482 feet were refuted by officials from the Iranian Red Crescent and Iranian investigators. On 20 February, two helicopters from

Islamic Revolutionary Guard Corps The Islamic Revolutionary Guard Corps (IRGC; fa, سپاه پاسداران انقلاب اسلامی, Sepāh-e Pāsdārān-e Enghelāb-e Eslāmi, lit=Army of Guardians of the Islamic Revolution also Sepāh or Pasdaran for short) is a branch o ...

Air Force sighted the wreckage of the aircraft, below the peak of the mountains south of Noqol at an elevation of approximately . Another military helicopter sighted the wreckage and pinpointed the crash site. The aircraft was obliterated, with large portion of the tail cone, the

vertical stabilizer A vertical stabilizer or tail fin is the static part of the vertical tail of an aircraft. The term is commonly applied to the assembly of both this fixed surface and one or more movable rudders hinged to it. Their role is to provide control, s ...

, the

rudder A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally air or water). On an aircraft the rudder is used primarily to counter adve ...

and the

empennage The empennage ( or ), also known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an arrow.Crane, Dale: ''Dictionary of Aeronautical Terms, third e ...

were found. Scattered bodies could be seen around the wreckage. No survivors were seen at the crash site. All 60 passengers and 6 crew members on board died. As helicopters were unable to land on the crash site, the recovery of the victims had to be done on foot. Officials stated that the bodies had to be carried on the rescuers' backs to the mountain foot. The head of the country's emergency services said that the recovery of the victims would be challenging due to the adverse weather. As of 21 February, at least 32 bodies had been recovered from the crash site. On 3 March, Iranian officials announced they had found the flight recorders.

Investigation

President of Iran Hassan Rouhani ordered Iranian Minister of Roads and Urban Development Abbas Ahmad Akhoundi to lead the investigation.

Iran Civil Aviation Organization The Civil Aviation Organization of Islamic Republic of Iran (CAO.IRI), ( fa, سازمان هواپیمایی کشوری جمهوری اسلامی ایرانBEA also sent 7 delegations to investigate the crash. The aircraft's manufacturer,

ATR ATR may refer to: Medicine * Acute transfusion reaction * Ataxia telangiectasia and Rad3 related, a protein involved in DNA damage repair Science and mathematics * Advanced Test Reactor, nuclear research reactor at the Idaho National Laboratory, ...

, sent 4 people to Iran to assist with the investigation. Initial assessment didn't find any abnormalities on the aircraft's structure. Flight control failure and power system malfunctions were also not reported by the crew. The assessment did, however, reveal that the flight had entered cloud with icing condition prior to its landing. The flight crew tried to fly in an unallowable altitude to get out from the cloud and reached an unsafe altitude. As the aircraft was flying at the altitude, it encountered a series of updraft and downdraft, its airspeed decayed and it then entered a dangerous stall condition.

Weather

Data on the weather condition in the area were collected from the Iranian Meteorological Agency and from the airport dispatcher. Data were also provided from interviews of numerous individuals including pilots who had flown from and to Yasuj. Additionally, the Iranian counterpart was also assisted by the French METEO-SAT. METAR report retrieved by Iranian investigators showed that, during the dispatch of Flight 3704, the weather didn't meet the minimum criteria for a flight to Yasuj. Yasuj Airport is listed in the airline's operation manual as an airport with a minimum ceiling for an approach and landing at 11,000 ft. The ceiling at the time was broken (clouds cover at least 5/8 – 7/8 of the sky) with clouds reported at 9,000 ft. The report further stated that the condition in Yasuj would later deteriorate as cumulonimbus clouds were observed in the area, with thunderstorm, rain and hail would also occur. As the weather condition didn't meet the criteria, the crews of Flight 3704 should have diverted the aircraft to Isfahan in the north or

Shiraz Shiraz (; fa, شیراز, Širâz ) is the fifth-most-populous city of Iran and the capital of Fars Province, which has been historically known as Pars () and Persis. As of the 2016 national census, the population of the city was 1,565,572 p ...

in the south. As the flight path included mountainous terrain in the route, Flight 3704 would counter a mountain wave phenomena in the area. A mountain wave is a form of a

Lee wave In meteorology, lee waves are atmospheric stationary waves. The most common form is mountain waves, which are atmospheric internal gravity waves. These were discovered in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, above ...

that is resulted by a disturbance on the horizontal air flow. Mountain wave may poses threat to the safety of a flight as it can lead to severe turbulence, icing, strong windshear, and updraft and downdraft motion to the aircraft. The high elevation of the mountain at the flight path indicated that the mountain wave was a hazard for the safety of the flight. To counter the phenomenon safely, the flight crews should’ve flown the aircraft at a minimum airspeed while monitoring the airspeed closely to prevent a stall condition. Vol d'onde

Analysis on Flight 3704’s FDR confirmed that the aircraft indeed had encountered mountain wave. The data revealed that the flight encountered an updraft and a downdraft motion created by the phenomenon. Further analysis by Iran Meteorological Report stated that an unstable layer, turbulence and freezing level at an altitude of 11,000 ft were predicted. French Meteorological Agency stated that the weather condition in the area of the accident at the time was favorable for severe icing condition. However, even though severe icing condition was present at the time, the Aircraft Performance Monitoring (APM) simulation of the flight conducted by investigators suggested that the aircraft's decrease of performance was more likely caused by external gradient such as wind. The mountain wave in the area caused a vertical wind with speed as high as 3,000 ft/min. The simulation revealed that as the aircraft flew over the mountain, a downdraft struck the aircraft and the nose pitch increased to maintain the flight altitude. As it entered a stall condition, the crew then made a nose down pitch to counter it. The EGPWS was later activated until the end of the flight.

Crew performance

The assessment of both pilots' behavior prior to their flights didn't indicate any abnormalities. Investigators, however, did find that the crews had never been trained on how to execute an appropriate response when a mountain wave struck the aircraft. The crew was not familiar with mountain wave and the manual also didn't provide information regarding the phenomenon. The ATR simulation also did not provide the crews with simulation on handling a mountain wave. Prior to its approach to Mount Dena, the First Officer of Flight 3704 had made several recommendations to the Captain on several instances. The Captain didn't respond at any of the given recommendations and decided to ignore it. The lack of communication between the Captain and the First Officer indicated a steep authority gradient phenomenon in aviation, which may be caused due to difference in flying experience. It was evident that the crew of Flight 3704 had deviated from its operating manual. During Flight 3704’s approach to Mount Dena, the ATC had given clearance for the flight to fly at FL170. ATC later informed the crew that the ceiling was at 15,000 ft. The CVR recording revealed that the crew decided to descent further to an elevation of 15,000 ft so that the aircraft would get out of clouds. The minimum altitude for the airport however was 15,500 ft, so the crew was going to fly under the approved minimum altitude. During its descent, the aircraft encountered an updraft and later a downdraft. The downdraft was strong enough to cause the nose pitch to rise. As the pitch was increased by the force of the downdraft, the airspeed decreased and the drag force increased accordingly, risking a stall condition to occur. As the power lever was increased to counter the low speed of the aircraft, the pitch kept increasing and the airspeed kept decreasing, at one point reaching 118 knots. The nose pitch reached +15 degree. While the crew tried to counter the stall condition by bringing the nose down, the crew didn't execute the recovery properly. The engine was not in full power and the flaps were not set to 15 degree. It was presumed that the crew didn't expect to encounter a mountain wave phenomenon in the area and thus this might have decreased their situational awareness. As the pilots tried to save the aircraft by bringing the nose down, there was no more altitude left for a safe recovery.

Conclusion

The Iranian Civil Aviation Organization published the interim report, with the following: The investigation also noted that, while mountain wave phenomenon rarely cause an aircraft to crash, the phenomenon is rarely, if not ever, addressed to pilots. Many pilots are unaware of the phenomenon and flight manuals did not educate pilots enough on the matter. The Iranian CAO issued 28 recommendations in response to the crash. Among the recommendations were: * ICAO should include the hazard of mountain wave in every flight manual and also should make sure that the retrieval of essential aircraft parts are not affected by an economic embargo * EASA should revise the stall recovery procedure of an ATR 72-212 * Iran CAO should develop an Aviation Search and Rescue program to ensure a better coordination with the search and rescue operation * Every airliners in Iran should include a training program which address the hazards of mountain wave. The final report, published in 2020, had the same findings, albeit with minor rewording. The final report also had comments from the BEA.

Aftermath and reactions

On 23 February 2018, the Iran Civil Aviation Organization temporarily suspended the operation of Iran Aseman Airlines' ATR 72 aircraft. The search and rescue operation was viewed as "too long" by some family members, some were angered due to the incompetent handling of the disaster. On 19 February, more than 100 people reportedly protested outside a government building in Dena Kooh, demanding Iranian officials to step down due to the response on the disaster. Journalists have speculated that the economic

sanctions against Iran There have been a number of sanctions against Iran imposed by a number of countries, especially the United States, and international entities. Iran was the most sanctioned country in the world until it was surpassed by Russia following its inva ...

which have prevented Iranian airlines from obtaining new planes and spare parts and forced them to operate aging aircraft may have contributed to the cause of the crash. Iranian judicial authorities and the special committee of the Islamic Consultative Assembly believed that the flight should not have been allowed in the first place, and blamed the Iran Aseman Airlines for the accident. Iranian Parliament investigation report on the incident, released on May 18, 2020, blamed Iranian Civil Aviation Organization and Aseman Airlines on the incident. The parliament report also accuses the manufacturer of the aircraft for not providing spare parts for the maintenance of the aircraft.

References

External links

*
Accident Investigation Report Issued 17 February 2019
*
Accident to the ATR72 registered EP-ATS and operated by Aseman Airlines on 18/02/2018 near Yasouj [Investigation led by AAIB / Islamic Republic of Iran
/nowiki>]" – Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile *
Accident de l’ATR72 immatriculé EP-ATS et exploité par Aseman Airlines survenu le 18/02/2018 près de Yasouj [Enquête menée par AAIB / République Islamique d'Iran
/nowiki>]" – Bureau d'Enquêtes et d'Analyses pour la Sécurité de l'Aviation Civile {{Aviation accidents and incidents in 2018 2018 in Iran Accidents and incidents involving the ATR 72 Accidents and incidents by airline of Iran Aviation accidents and incidents in Iran Aviation accidents and incidents in 2018 February 2018 events in Iran Semirom County Airliner accidents and incidents caused by pilot error Airliner accidents and incidents caused by stalls