Turkey bid farewell to four military officers who were killed when their fighter jets crashed on Tuesday during a training mission. A military funeral ceremony was held yesterday for Major Salih Sezer and First Lieutenants Onur Özkaya, Zeynel Özbahçeci and Yasin Atalay before their bodies were flown to their hometowns. Chief of Staff General Necdet Özel and Minister of Defense İsmet Yılmaz attended the ceremony in the eastern province of Malatya, home to the air base where the officers were stationed.Although the causes are not yet known, the crashes of two RF-4E jets in eastern Turkey on Tuesday have been added to the list of 11 crashes involving aircraft decommissioned by other countries, raising concerns on their airworthiness despite modernization.On Tuesday evening two RF-4E jets on a training flight crashed in the countryside in Malatya. Four military officers aboard the two aircraft were killed in the crash.An investigation was launched into how the two jets, which disappeared from radar about one hour before the accident, crashed and whether they collided mid-air.The crashes raised concerns about how safe the aircraft are as 11 RF4-Es have crashed between 1995 and 2015. Six officers were killed in those accidents, which were both mid-air collisions and crashes.The jets, a sub-class of F-4 Phantom, have been used by the Turkish Air Force since 1980 for reconnaissance and training missions. Turkey purchased eight aircraft from the United States that year and 46 more were purchased from Germany between 1992 and 1994 after the German air force ended decommissioned them. Thirty-two aircraft bought from Germany were modernized and the remaining ones were used for spare parts. Between 2009 and 2011 16 aircraft underwent another modernization process. They were expected to be entirely decommissioned by the end of this year after three of them were discarded. All of the remaining 13 aircraft were used for training missions at Erhaç air base in Malatya.The aircraft were obtained as part of Turkey's efforts to modernize its fleet after it joined NATO in 1952. F-4 Phantoms made a name for themselves in the Vietnam War, and Turkey mostly purchased airplanes built in the 1970s, but instead of discarding the aircraft and buying new ones, Turkey opted to modernize them in the 1990s to cut costs.