Seattle, Washington - According to the FAA report, cockpit screens of Boeing 737 NG series jets go blank during westwards landings at some airports.
According to the report, a software bug causes the incident when the flight crew tries to program the autopilot to follow a selected instrument approach to the seven runways of which five in the United States and two are in South America (Colombia and Guyana).
Instrument approach procedures allow planes to conduct safe landings in all weather conditions regardless of visibility.
All six display units (DUs) blanked with a selected instrument approach to a runway with a 270-degree true heading, and all six DUs stayed blank until a different runway was selected,
The FAA's airworthiness directive summarizes three incidents that happened during landings at Barrow Airport, Alaska, in 2019.
Although full technical details were not given in the airworthiness directive, the FAA said that the seven runways had "latitude and longitude values" that "triggered the blanking behavior, suggesting some kind of memory interaction between onboard computers causing the screens to stop displaying any information until a different runway was selected in the flight plan.
Runways where Boeing 737 Next Generation aircraft are not supposed to land. Source: FAA
The bug affects 737-600, -700, -700C, -800, -900 and -900ER series jets, which are running Common Display System Block Point 15 (CDS BP 15) software for their display electronic units (DEUs) together with flight management computer (FMC) software version U12 or later.
FMCs hold the flight plan, thus navigating the airplane from waypoint to waypoint. DUs are the main screens displaying aircraft information to the pilots and are powered by two DEUs, each of which serves three of the DUs.
In the airworthiness directive, the FAA said it had confirmed that the faulty version of DEU software has already been removed from all airplanes conducting scheduled airline service into the affected airports" in the US.
Commercial jet airliners are far from immune to software bugs. Infamously, Boeing's 787 Dreamliner needed power cycling every 248 days to prevent the aircraft's electronics from powering down in flight, while Airbus' A350 was struck by a similar bug requiring a power cycle every 149 hours to prevent avionics systems from partially or even totally failing to work.