Airworthiness Directives; Learjet Model 23, 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, and 25F Airplanes

The FAA is adopting a new airworthiness directive (AD) for certain Learjet Model 23, 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, and 25F airplanes. This AD requires replacement of the spherical accumulator for the main hydraulic system with a new cylindrical accumulator. For certain airplanes, this AD also requires modification of the accumulator pressure gauge. This AD results from reports of the failure of two thrust reverser accumulators (which are similar to the main hydraulic system's spherical accumulator) and fatigue cracks found on four thrust reverser accumulators. We are issuing this AD to prevent failure of the spherical accumulator for the main hydraulic system, due to fatigue cracking on the threads, which could result in the loss of hydraulic power, damage to the surrounding airplane structure, and loss of airplane control. The failure of the accumulator could also result in injury to any persons in the surrounding area. The loss of hydraulic fluid could also leak onto a potential source of ignition and result in a consequent fire.