Citing “airworthiness concerns,” the Air Force has grounded its entire fleet of F-15s until the service can determine the cause of a crash involving a Missouri Air National Guard F-15C fighter on Nov. 2. According to the Los Angeles Times:
A couple of things to note. First off, it is not clear what caused the accident. There have not been nearly as many F-15 crashes as there are F-16 crashes; the Eagle has a very good safety record on account of its twin engines, high power-to-weight ratio, big wing (very forgiving at low speed and high angle of attack), and immense structural strength (the kind that allows the F-15E Strike Eagle to be flown at gross weights in excess of 81,000 pounds). It is very unusual for the Air Force to ground an entire fleet of aircraft after a single crash; usually there has to be a pattern of accidents pointing to a systemic cause. The fact that the F-15 appears to have disintegrated in mid-air may have prompted a precautionary grounding and inspection. While it is true that the F-15s now in service average more than 20 years of age, it is important to note that there are several different versions in service, and some are older and more worn out than others. The remaining F-15A and B models, built from the middle to late 1970s, have mostly been consigned to the boneyard, but some soldier on in the Air National Guard. It would be interesting to know the serial number of the Missouri Air Guard plane that broke up, which would tell us how old it was. The later F-16C and Ds, as well as the F-15E Strike Eagles, are newer and have fewer hours. In general, the F-15s have been very well maintained and have shown little evidence of fatigue. They periodically undergo block upgrades in which the airframe is effectively “zero-timed”, and, properly flown, they are practically indestructible. It is conceivable that an overlooked fatigue crack could cause a catastrophic failure, but these are seldom as clear-cut as a wing falling off. Instead, one might look to some lesser failure initiating a string of events culminating in disintegration. For instance, the failure of an elevator actuator might cause the elevators to lock in the full up or down position, resulting in very rapid pitch up or down, which would overstress the airframe. Or, an engine could suffer compressor blade failure, which would cause the engine to explode, sending bits of high-velocity metal into the wings and fuselage. There is no way of knowing until the accident investigation is completed. Until then, a temporary grounding and inspection is a prudent measure. These actually happen pretty regularly, and what makes this newsworthy is that it has not happened to the F-15 in the past (to my knowledge), as was the case with the F-16, the F-111, the AV-8 Harrier, and any number of other military jets. It is not surprising that the Air Force and its partisans would use the opportunity to bang the drum for accelerated F-22 acquisition. There is not doubt that the Raptor is badly needed to maintain the qualitative edge of the U.S. Air Force over potential competitors (e.g., China, India, Venezuela) flying aerodynamically advanced aircraft such as the Su-30 Flanker (see my earlier piece on Chinese air defense). The question is really how many and how quickly. Given the cost of the F-22, there is little possibility of replacing the Eagle on a one-for-one basis, but we should get enough to provide a sharp edge to our air superiority capabilities, in order to overmatch, and hopefully deter potential aggressors.
