The Federal Aviation Administration (FAA) has issued an airworthiness directive (AD) requiring US operators of the 737 Classic series to inspect their aircraft for possible wire failures. This advisory, issued late last week, comes as a result of the investigation of the Sriwijaya Air crash that took place in January 2021.
Actions resulting from the January crash in Indonesia
According to Reuters, the FAA requires carriers in the US who still operate 737 Classic jets to inspect aircraft for possible wire failures. The 737 Classic line-up, produced between 1984 and 2000, includes 737-300, -400, and -500 models. This generation was the second iteration of the 737 after the very first 737s were developed.
This AD is a response to investigation findings from Indonesia’s Sriwijaya Air crash in January, which saw a 26-year-old 737-500 crash into the Java Sea. All passengers and crew onboard, totaling 62, were killed in the incident. Much of the investigation has surrounded the aircraft’s autothrottle system, which had issues prior to the aircraft’s fatal accident.
In a statement to Simple Flying, Boeing said,
“Boeing works to ensure that our airplanes are safe and meet all requirements. We are in constant communication with our customers and the FAA, and engaged in ongoing efforts to introduce safety and performance improvements across the fleet. Today’s airworthiness directive makes mandatory the guidance Boeing provided to the fleet in March.”
Wiring connected to the autothrottle system
The FAA is requesting that operators verify that the flap synchro wire, which has a role in operating the aircraft’s autothrottle system, is securely connected to a safety sensor. Failure of this wire could go undetected by the autothrottle computer, posing a safety risk on affected airplanes.
The FAA does acknowledge, however, that there has yet to be evidence from the crash indicating that issues with the flap synchro wire had a role in the accident. Nonetheless, the possibility of a failed connection would pose a safety risk, thus warranting action.
The aviation regulator notes that a faulty connection could result in the failure of the autothrottle system’s ability to detect the position of the aircraft’s flaps if the aircraft’s engines were operating at different thrust settings due to another malfunction.
On March 30th, Boeing directed operators to perform electronic checks of the autothrottle computer to confirm the wire was connected within 250 flight hours. The FAA will require the initial test within two months from the date of the AD or within 250 flight hours, whichever comes first.
After initial inspections, the FAA will require subsequent checks every 2,000 flight hours.
Over 1,000 aircraft worldwide affected
The FAA notes that there are 143 737 Classic series airplanes in the US that require inspections. Worldwide, there are 1,041 aircraft that could be affected. However, due to the ongoing global health crisis, some of these may be inactive or in long-term storage.
When it comes to operators in the US, Reuters notes that Aloha Air Cargo, DHL, iAero Airways, Kalitta Charters, and Northern Air Cargo currently operate 737 Classic aircraft.
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