A Russian-built MiG-29 bought and refurbished by Iran crashed during a test flight on Wednesday, two days after an advanced Sukhoi Su-57 stealth fighter crashed during a test flight in eastern Russia.

The Su-57 crashed in the Khabarovsk region of eastern Russia due to what Russian state media described as a failure in its steering system. It was among the first Su-57s to come off the production line after more than a decade of development.

A total of ten of the planes have been built at the Sukhoi plant in Khabarovsk, with another 76 to be delivered over the next ten years, and more possibly built for sale to Russia’s arms customers. Some of the early Su-57s were tested in limited combat exercises during Russia’s intervention in Syria.

The plane that crashed on Monday was reportedly being flown by a civilian pilot for “factory trials.” It was the first known crash of an Su-57. The pilot was able to eject safely.

The Su-57, code-named “Felon” by NATO, is a fifth-generation twin-engine fighter intended to compete with America’s F-22 Raptor. Like the F-22, the Su-57 has design elements that give it very small radar and heat signatures, and it combines a high degree of maneuverability with an extensive inventory of weapons – it can dodge and throw a punch. The Su-57 had a troubled and secretive design process, but it is believed to trade some of the F-22’s stealth for increased speed and agility.

The Iranian crash involved a much older MiG-29 that was launched from Tabriz airbase in northwestern Iran and went down in the Sabalan mountains near the border with Azerbaijan, not far from a dormant volcano.

Early reports said the Iranian plane had two pilots and both were killed, but this was later revised to say that at least one of the pilots was alive and able to send a message back to base after the crash.

A rescue mission involving ground teams and helicopters was dispatched to recover the pilot, who was described as an experienced military officer. On Thursday the Iranian military announced the “martyrdom” of the pilot, who was identified as Col. Mohammad Reza Rahmani of the Islamic Republic of Iran Air Force (IRIAF).

The cause of the crash is reportedly under investigation. The Iranian military’s account of the unsuccessful mission to rescue Rahmani from the mountains mentioned “severe weather conditions,” while a military source told Iranian media the plane experienced some kind of malfunction.

The Jerusalem Post noted that Iran’s air force is “made up of aging planes, and it cannot afford to lose them.” Thanks to Iran’s turbulent history in the last decades of the 20th Century, it has a mixture of old American and Russian warplanes. The latter were acquired with great difficulty by Iran during the 1980s due to American diplomatic pressure and have been kept in service with periodic overhauls.