On June 29th, the Russian Air Force allowed its Su-24 aircraft into the air once more. The Su-24s had been grounded for ten days while the causes of two accidents were investigated. The first of these occurred on June 17th, when a Su-24 bomber crashed while landing. The Russian Air Force did not ground all Su-24s, until an investigation to determine if there was a problem with all aircraft of this type. Two days later, another Su-24 crashed while trying to land. At that point, all Su-24s were grounded pending investigation results. It was found that the first crash was the result of pilot error. The second crash was caused by a failure in the wing positioning system. In short, there was not common cause that was likely to be found in all Su-24s. But the Su-24s are getting old. In the last ten years, there have been 13 Su-24 crashes.
Less than two years ago, the Russian Air Force began receiving twelve upgraded Su-24 fighter-bombers. The improvements included modern electronics (all digital, flat panel screens, GPS and so on). The aircraft were also equipped to deliver all the latest smart bombs. Russia wants to get the most out of the few flyable Su-24s it still has in service. Three times that year (2007), all Russian Su-24 bombers were grounded because one of them had crashed. Su-24s have been in service for 34 years, and less than a third, of the 1,400 manufactured, are still technically in service. But, like the U.S. F-15Cs (about the same age as the Su-24), older aircraft get cranky and unreliable.
The Su24 was something of an "F-111 Lite" when it first showed up during the Cold War. The 43 ton, swing-wing bomber has a crew of two and can carry up to eight tons of weapons. The aircraft has inefficient engines, and lots of 1980s vintage electronics. When everything worked, the Su-24 was an all-weather bomber capable of delivering dumb bombs quite accurately. Most of the time, everything didn't work. The new upgrade (the Su-24M2) hoped to fix that. It sort of did, but most of the Su-24 fleet is simply too old. The Su-34 is to replace the aging Su-24s, but only when money is available to purchase the new aircraft. That might not be for five years or more.