..THE PROPOSAL RELATE TO CRACKS IN STRINGERS
The Federal Aviation Administration (FAA) has proposed a new airworthiness directive (AD) for all Boeing 747-8 models. According to a notice issued on April 6th, the matter relates to both 747-8i and 747–8F series aircraft.
As per the Federal Register, the FAA has issued a notice of proposed rulemaking (NPRM) following the reporting of “cracks in stringers, common to the end fittings, forward and aft of the pressure bulkhead at station (STA) 2360 at multiple stringer locations.”
The FAA added: “This proposed AD would require repetitive inspections of stringer sidewalls and certain stringer assemblies, common to the end fittings, forward and aft of the pressure bulkhead at STA 2360 for any crack, and applicable on-condition actions.”
Stringers are often mistakenly referred to as their structural counterparts, longerons. They run longitudinally across the fuselage or spanwise of an aircraft wing. They are structural parts that shift loads and stresses from the plane’s skin to its formers. The agency summarized that it proposes addressing what it calls an unsafe condition. It has asked for comments on the matter by May 22nd.
A WORD FROM BOEING
Simple Flying reached out to Boeing for comment on the situation. The company replied with the following statement: “We support the proposed rule, which would align with guidance we shared with our customers in 2021 and 2022.”
The FAA added that following an investigation, it has been determined that during assembly, un-shimmed or incorrectly shimmed gaps larger than what is required caused "excessive and sustained internal tensile stresses and resulted in stress corrosion cracking in the stringers."
If unaddressed, the situation could end in an undetected crack in the stringers that could cause difficulties for the structural element to sustain limit load, which could "adversely affect the structural integrity of the airplane."
System-wide inspection of Boeing's 787 shimming also contributed to the delay of Dreamliner deliveries in 2021. These initial shimming problems and a lack of flatness in structural joints then led to flaws being found in the aircraft's tail.
Still, this 747-8 shimming issue is unrelated to issues on other Boeing aircraft models. Notably, it did not have an impact on production.
ACROSS THE INDUSTRY
This move by the FAA followed a series of AD proposals last year. In November, the group published a document concerning the inspection of skin lap splices across 737 Next Generation (NG) aircraft. The FAA shares that there were reports hinting at fuselage skin cracking on some units.
Moreover, in December, the FAA proposed an AD regarding 787 Dreamliner water leaks. The proposal was issued following reports of a loss of water pressure during operations and water leaks impacting electronic equipment.
It has now been 13 years since the 747-8 first flew. It was manufactured to be more efficient and environmentally friendly than the aging 747-400. The cargo 747-8F was the first to fly, hitting the skies on February 8th, 2010, before entering service with Cargolux on October 12th, 2011. The passenger 747-8i performed its maiden flight on March 20th, 2011, before being introduced with Lufthansa on June 1st, 2012.
In total, 155 units of the 747-8 have been built. The final production rolled off the line on January 31st this year, bringing the 747 program to a close.
In the passenger space, the likes of Air China, Korean Air, and Lufthansa remain prominent operators of the 747-8i. Meanwhile, the 747-F is spotted on numerous crucial cargo routes across the globe.
Source: By Sumit Singh Published Apr 14, 2023