First an Iran Air Airbus A300-600, registration EP-IBC performing flight IR721 from Tehran Imam Khomeini (Iran) to Frankfurt/Main (Germany), was climbing out of Tehran when the crew stopped the climb at about FL190 reporting a strong odour on board. The aircraft returned to Tehran Imam Khomeini for a safe landing about 30 minutes after departure.
A replacement Airbus A310-300 registration EP-IBL reached Frankfurt with a delay of 11 hours.
For the flight back to Tehran, a replacement Airbus A300-600 arrives from VIE to fly the passengers back to Tehran (IKA)
And fly them back to Tehran: