More bad news for the US Air Force's aging aircraft fleets.
I'm sure everybody remembers the infamous longeron-cracking that grounded the entire Boeing F-15 fleet in November, which for a time left (gasp!) Oregon's air space briefly undefended.
Less strenuously reported is the worsening structural condition of growing numbers of older-model Lockheed Martin F-16s. Cheers to Graham Warwick for forwarding this snippet of written testimony from a Congressional hearing earlier this month. The writing is attributed to "Daniel J. Darnell Deputy Chief of Staff Air, Space and Information Operations, Plans and Requirements Headquarters, U.S. Air Force."
Wing pylon rib corrosion, a known problem with the F-16 aircraft is an issue we monitor closely. This corrosion prevents the F-16s from carrying pylon mounted external fuel tanks, which limits their effective combat range. While we currently have three F-16 aircraft grounded due to wing pylon rib corrosion, the corrosion problem is somewhat common across the fleet. For example, within the past 24 months, we identified 27 aircraft at Aviano Air Base, Italy with this problem. We currently inspect F-16 aircraft every 800 hours to monitor for this problem. Because of inspections, we have also found approximately 16% (69 of 399) of our Block 40/42 F-16 aircraft now have bulkhead cracks. This discovery has led to 22 Block 40/42 F-16 aircraft grounded due to the severity of the cracks. An additional 41 aircraft continue to fly with flight restrictions. We will continue to monitor this situation closely.
Now comes the news this week that the relatively young C-17 fleet is also dealing with a structural problem.
General Arthur Licthe, chief of Air Mobility Command, told lawmakers this week that stress imposed by the C-17's thrust reversers have spawned fuselage cracks in the airframe. I asked Boeing for elaboration, and here's what they told me:
Thanks for your question on the C-17 fatigue cracks. The stress cracks, beneath and forward of the wings on the C-17 fuselage are a minor occurrence and don’t pose a safety hazard for the aircraft or flight crews. Boeing has developed a fix for the problem and the fix has been demonstrated and validated to meet the durability requirements. There’s no impact on the operational readiness of these planes and the cracks are being fixed during regularly scheduled maintenance with a simple technique.
I also asked Boeing why the thrust reversers would lead to fuselage cracks forward of and beneath the wings. Boeing's reply:
It’s referred to as the "fire hose effect." The reversed air, from the fan thrust reverser, glances off the fuselage forward and below the wing. The resultant stresses in the fuselage skins due to this impingement were higher than anticipated and have resulted in the small skin cracks.