Summary
We propose to adopt a new airworthiness directive (AD) for certain Hawker Beechcraft Corporation (Type Certificate previously held by Mitsubishi; Raytheon Aircraft Company) Model MU-300 airplanes, and Hawker Beechcraft Corporation (Type Certificate previously held by Raytheon Aircraft Company; Beech Aircraft Corporation) Model 400, 400A, and 400T airplanes. This proposed AD was prompted by multiple reports of fatigue cracking in the horizontal stabilizer ribs. This proposed AD would require repetitive inspections of the horizontal stabilizer rib assemblies for cracking, and replacement if necessary. We are proposing this AD to detect and correct such cracking, which could result in the failure of the horizontal stabilizer and loss of pitch control of the airplane.