The Federal Aviation Administration (FAA) has issued a new Airworthiness Directive (AD) for all Boeing Model B-17E, B-17F and B-17G aircraft recommending “inspections of the wing terminal-to-spar chord joints” to “address the unsafe condition on these products”.

It is estimated that this AD affects 18 US aircraft, of which only three are currently in flying condition; the youngest of which – Michigan-based Yankee Air Museum’s B-17G Yankee Lady – was temporarily grounded in April 2023.

During 2021, walk-around checks performed prior to takeoff of B-17G Aluminum Overcast discovered that the left wing had “shifted away” from the fuselage by about two inches. When both wings were removed in 2023, further inspection found “complete separation of the left front spar lower fitting at the wing-to-fuselage joins as well as additional cracking on the equivalent joint on the right side of the airplane”.

In recognition of the severity of this condition – which could result in fatigue cracking of the wing terminal-to-spar chord joints, potentially resulting in “loss of control of the airplane and reduced structural integrity” – this FAA AD has been issued to cover all B-17s, including those operated under experimental airworthiness certificates.

The AD requires inspection of the wing terminal-to-spar chord joints to detect cracking and corrosion, using one of two methods: a “magnetic particle inspection of the terminal fittings and an eddy current inspection of the spar chord”, or “an eddy current bolt hole inspection on the steel terminal fittings and the aluminum spar chord”.

Any cracking and corrosion must be repaired, and regardless of the inspection method, all results (both positive and negative) must be sent to the FAA. Estimated compliance costs are detailed in the table below, and the FAA predicts “most operators will chose to do the eddy current bolt hole inspections, which do not require major disassembly”.