Summary
We propose to adopt a new airworthiness directive (AD) for all The Boeing Company Model 747-400, 747-400D, and 747-400F airplanes. This proposed AD was prompted by a report of a 13.4-inch crack in the left wing front spar web inboard of pylon number 2 between front spar station inboard (FSSI) 655.75 and FSSI 660, found following a fuel leak. This proposed AD would require repetitive detailed, ultrasonic, and high frequency eddy current inspections for cracking of the front spar web between FSSI 628 and FSSI 713, and repairs if necessary. We are proposing this AD to address the unsafe condition on these products.