Summary
We propose to supersede an existing airworthiness directive (AD) that applies to all The Boeing Company Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. The existing AD currently requires repetitive inspections to detect cracking of the lower corners of the door frame and cross beam of the forward cargo door, and corrective actions if necessary. The existing AD also requires eventual modification of the outboard radius of the lower corners of the door frame and reinforcement of the cross beam of the forward cargo door, which would constitute terminating action for the existing repetitive inspections. Since we issued that AD, we have received additional reports of fatigue cracking in the radius of the lower frames and in the lower number 5 cross beam of the forward cargo door. This proposed AD would revise the compliance times for the preventive modification; add certain inspections for cracks in the number 5 cross beam of the forward cargo door; and add inspections of the number 4 cross beam if cracks are found in the number 5 cross beam, and corrective actions if necessary. For certain airplanes, this proposed AD would also add a one-time inspection for airplanes previously modified or repaired, and a one-time inspection of the reinforcement angle for excessive shimming or fastener pull-up, and corrective actions if necessary. We are proposing this AD to prevent fatigue cracking of the lower corners of the door frame and number 5 cross beam of the forward cargo door, which could result in rapid depressurization of the airplane.