Iran A306 at Tabriz on Oct 23rd 2023, smoke in cockpit and cabin

Last Update: April 14, 2024 / 09:08:20 GMT/Zulu time

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Incident Facts

Date of incident
Oct 23, 2023


Iran Air

Flight number

Aircraft Registration

Aircraft Type
Airbus A300

ICAO Type Designator

An Iran Air Airbus A300-600, registration EP-IBA performing flight IR-718 from Istanbul (Turkey) to Tehran Imam Khomeini (Iran), was enroute at FL330 near Tabriz (Iran) when the crew decided to divert to Tabriz reporting smoke in cockpit and cabin. The aircraft landed safely in Tabriz.

Iran's CAO reported the same happened again on the onward flight to Tehran after a mechanic had released the aircraft. The occurrence was rated a serious incident and is being investigated by the CAO.

On Apr 14th 2024 The Aviation Herald received Iranian CAA/AAIB's final report into the occurrences concluding the probable causes of the serious incidents were:

The investigation of the serious incident was conducted by AAIB based on the Annex 13 to ICAO Convention, notification was sent to the French Investigation Bureau (BEA) as the State of Manufacture and Design, and so far, an accredited representative and his adviser from Airbus Co. were introduced accordingly. The related cooperation between the two investigation authorities was made and hereupon the final report has been issued.

The Cause of incident was entering smoke into the hot air system of cabin due to oil leakage from the broken bearing manifold of the left engine.

The AAIB summarized the sequence of events:

On 23 Oct 2023 at 10:17 UTC, the Airbus A300B4-605R with registration mark EP-IBA flight No. IR718 operated by Iran Air took off from Istanbul/Turkey Airport (IST) with 211 passengers and 15 flight crew onboard to conduct a scheduled passenger flight to Tehran Imam Khomeini International Airport (IKA).

According to the Pilot in Command’s recorded statements; at 11:59 UTC, before entering Tehran FIR and when flying at an altitude of 33000 feet in the latitude N39.1120 and the longitude E39.3262, warning smoke was detected by the system in Minimum Equipment Bay and then by AVIONIC smoke , LAVATORY smoke and subsequently smoke was observed in the cockpit and the cabin. So, cockpit crew used oxygen masks and the Pilot in Command (PIC) requested an emergency landing at Tabriz Airport as the alternate airport of the route.

At 12:23 UTC, aircraft made an emergency landing at Tabriz Airport (TBZ) and all passengers were disembarked to the transit hall. Then, all related inspections and technical assessments were carried out by the onboard technical staff while the air conditioning system of aircraft was evaluated at low engine RPM.

Finally, due to the good cabin air quality and its normal conditions, aircraft was released to fly by the onboard authorized technical staff.

At 18:10 UTC, aircraft took off from Tabriz Airport (TBZ) to Tehran Imam Khomeini Airport (IKA) with 185 passengers and 15 flight crew onboard (26 passengers disembarked the flight).

At 18:21 UTC, about 11 minutes after takeoff, at an altitude of 23000 feet, aircraft experienced real smoke in the cabin and cockpit again, so aircraft returned to Tabriz and successfully landed at 18:42 UTC. Aircraft was grounded at TBZ airport for further investigation.

The AAIB analysed:

Operational Analysis:

The Istanbul-Tehran flight began from Istanbul without receiving any warning from aircraft's smoke control system and aircraft reached to cruise flight level. While aircraft descend from FL350 to FL330, smoke was observed in the cockpit and the pilots received a smoke warning from the relevant systems. According to the pilot's report in aircraft technical logbook (ATL), the pilot recorded these defects:

“During cruise, min equipment bay smoke, followed by avionic smoke & lavatory smoke faults with real existence of smoke in the cockpit & cabin”

According to the Pilot in Command (PIC) note:

At the time of descending to FL330 from Ankara Center, the co-pilot had left the cockpit as necessary, and another pilot was in the cockpit instead. At this moment, first the treble chime sound was heard, the “Minimum Equipment Bay Smoke” guidance was appeared on the ECAM, and then, the cockpit was filled by smoke. The PIC immediately switched on the “Seat Belt” sign, turned off the Gall Power system, wore the oxygen mask, and informed the Chief Purser (CP) of the matter.

The first option the came to the PIC’s mind was landing at Urmia or Tabriz airports as nearest airports. Due to encountering a CB cloud the PIC had turned on the weather radar of aircraft, so he turned it off as his first action to solve the problem with the idea that maybe the weather radar had been the cause of smoke.

The PIC called the Chief Purser (CP) to ask the co-pilot to return to his seat, and then, asked the co-pilot to make operative the sniffer fan. The co-pilot stated that no smoke was observed in the sniffer, however, the PIC asked him to check it one more time, and the co-pilot stated again that no smoke was observed in the sniffer. At the same time, “Avionics Smoke” and Lavatory Smoke” alerts were appeared on the ECAM.

Thereupon, on the basis of the “Flight Crew Techniques Manual (FCTM)” and noting the fact that smoke alerts had been appeared on the ECAM which could be considered a sign of “Air Conditioning Smoke”, the pilots referred to the Quick Reference Handbook (QRH) and applied the related instructions of dealing with smoke, so that the smoke were disappeared. the flight crew has not immediately and clearly identified the source of the event and were not able to isolate it, and decided to divert to Tabriz as alternate airport. Once the diversion was initiated, the flight crew entered the identification and isolation part of the SMOKE / FUMES procedure in order to identify the origin of the event. The identification was not undertaken by isolating different systems and assessing the smoke dissipation completely due to disappearance of the smoke.

Afterwards, the PIC contacted Tehran Control Center and announced “Mayday” to be considered in priority and finally, aircraft landed safely at Tabriz Airport, where all the possible smoke generating systems were checked by technicians and smoke source troubleshooting was conducted. Ensuring correct operation of the related systems, and in coordination with the maintenance & flight operation unit, aircraft was released to fly to Imam Khomeini International Airport (IKA).

After performing initial flight procedures, aircraft took off from Tabriz Airport and was cleared for FL230. Requesting for FL250, smoke was observed again. Applying the “Removal of Smoke/Fumes Manual”, the PIC decided to return to Tabriz Airport. Based on his experience from the previous flight, and considering the fact that smoke was intermittently observed and disappeared, the PIC assumed it as the “Air Conditioning Smoke” and turned off both of the packs while flying on FL150 and less, and smoke was totally disappeared.

According to the conversations between the pilots recorded on the CVR and on the basis of the investigations conducted on the data recorded on the FDR, the pilots’ interviews, flight documents and aircraft, the following findings were obtained:

1- Considering that the event has occurred before entering Iran FIR, the pilots decided to land in nearest suitable airport in their route.
2- Based on the civil aviation authority’s AIROPS regulation and the Operations Manual (OM) of the airline, audio files of the CVR were not saved.
3- The CVR was saved by the investigators of aircraft Accident Investigation Board (AAIB) as soon as they reached to aircraft, but due to duration of time since the emergency landing and as the result, the CVR had been overwritten, all cockpit voice and communications related to Istanbul-Tehran flight were unavailable.
4- According to the CVR (Tabriz to Tehran flight returned again to Tabriz), the co-pilot requested to read the checklist on “Smoke/Fumes and it’s Removal ” which was agreed by the PIC, but due to flight preparation ,commencement of approach and landing and disappearance of smoke warning , the implementation of the checklist was not continued
5- On the next day, a ferry flight from Tabriz to Tehran was conducted by another instructor-pilot, according to the FDR and CVR of which, smoke was observed in the cabin while taxiing at Tabriz Airport. The instructor-pilot could eliminate the smoke by turning off the cabin fans and switching off the ECON flow of the #1 engine and proceeded to continue the flight, during which, by repeatedly switching on/off the ECON flow of the #1 engine , and observing smoke, the instructor-pilot realized that the smoke must be due to a problem in the engine number 1.

Technical Analysis:

After aircraft emergency landing at Tabriz Airport, an authorized aircraft mechanic who was onboard, initially tries for troubleshooting the unfavorable cabin air quality according to the heading 21-20-00 of the Troubleshooting Manual (TSM) of aircraft, in which, the origins of this problem have been caused by following items which considered by the mechanics:

- APU - Internal and external oil leaks or presence of grease inducts after APU change. (Not applicable)
- Engines - Internal oil leaks and presence of grease in ducts after engine replacement. (Not applicable)
- Ground carts - Internal oil leaks. (Not applicable)
- Hydraulic system - Pressurization line non-return valve leakage/failure and hydraulic tank overfilling. (May be applicable)
- Engine or APU ingestion of: (not applicable)
+ De-icing fluid into inlet.
+ Exhaust fumes from other aircraft, GPU.
+ Pollution (e.g., smoke from fires).
+ Hydraulic fluid leaks.
+ Birds.
+ Compressor wash procedures residues.
+ Pollens.
- Galley equipment, ovens, coffee makers, etc.(N/A)
- Damaged electrical wiring or components. (may applicable)
- Inappropriate or excessive use of CO2 (dry ice) by caterers or excessive quantities being transported. (N/A)
- Toilet fluid spillage, leakage and also unapproved mixing of different disinfectant fluids within the toilet. (N/A)
- Leakage of the rain repellent system or rain repellent contamination within the cabin or flight deck. (N/A)
- Spillages within cargo compartments. (N/A)
- Items stowed in overhead bins. (N/A)
- APU oil leaks into the bleed system. (N/A)
- Engine oil leaks into the bleed system(applicable).
- Contamination of the ECS. (May applicable)

Based on the above-mentioned guidance, the mechanic evaluated the related systems including hydraulic system according to the chapter 29-11-00 of aircraft maintenance manual (AMM) and did not observe any defects. Then, he performed engine run up on the ground and evaluated cabin air conditioning system but no problem was found, so he released aircraft for next flight according to aircraft Troubleshooting Manual (TSM). An inspection of the engine bleed air supplies as requested in the TSM was not performed, which may have allowed the oil leak at engine #1 to be detected.

After the instructor-pilot of the ferry flight informed the engineering department of the airline that the smoke had disappeared by turning off the bleed1 system, the possibility of failure in engine number 1 was considered, so the technicians performed a more detailed troubleshooting on it based on the heading AMM 72-21-01 of aircraft of the technical instruction and finally a fracture was observed in the bearing manifold of the engine number 1 with part number (PN);9196M44G03, which caused oil leakage into the hot air system entering into the cabin during aircraft’s ascend and descend. Due to the high temperature of internal area of the #1 engine, the leaked oil turned into smoke and entered into aircraft cabin air system.

Afterwards, the failed part was replaced by a new one and aircraft was released on 25 Oct, 2023 to perform a local flight without passengers, during which no technical problem was found and therefore aircraft was released for routine flight operation performance.

Finally, aircraft has performed several domestic and international flights during which, the mentioned problem has not been observed anymore.
Incident Facts

Date of incident
Oct 23, 2023


Iran Air

Flight number

Aircraft Registration

Aircraft Type
Airbus A300

ICAO Type Designator

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