Boeing is working on updating 747 flight computer software to eliminate an issue introduced in the software’s most recent version that causes both of the aircraft’s computers to reset in-flight.
The problem was introduced in Block Point 4.0 software developed for next generation flight management computers (NG FMCs). That version was rolled out in early 2019, in part to solve a similar issue in a previous version. But the Block Point 4.0 software, installed on all 139 747-8s and about 180 747-400s equipped with NG FMCs, is linked to a new problem.
“With the introduction of the new 4.0 software, operators reported a new issue that resulted in resets,” Boeing said. “After careful analysis of the software update and a review of in-service fleet data, we are making additional improvements to the software to further improve airplane safety and performance. We continue to work diligently with the FAA, our supplier and operators to ensure the software meets all safety and regulatory requirements.”
Honeywell supplies the 747 program’s NG FMCs.
FMC resets are common and present different risk levels. The current 747 NG FMC issues are “cold-start” resets, which a Honeywell article on the issue describes as three software exceptions occurring within one minute of each other. In some cases, the FMC recovers and all relevant information, including flight plans and performance, is retained. But some cold starts result in complete data loss.
If only one FMC has an issue, data from the stable FMC is synced. The 747s are experiencing dual-resets, however, including some reports of issues during critical phases of flight, such as takeoff and landing.
Boeing confirmed it has received reports of "about a dozen" dual resets involving the Block Point 4.0 software since its introduction in early 2019. “In each occurrence, the pilots were able to land the airplanes safely using established procedures,” the company said.
In each of the instances, flight plans were "deactivated" and performance data deleted, Boeing said.
Boeing said it has notified operators and the FAA about the incidents. The agency issued a draft airworthiness directive in August 2019 mandating the Block Point 4.0 software upgrade based on Boeing operator bulletins sent out in February 2019. Boeing suggested operators upgrade within six months. But the mounting reports convinced the agency to withdraw the proposed rule while Boeing works on a fix.
“The manufacturer is developing new software to resolve the unsafe condition,” the FAA said in an Oct. 20 announcement. “In light of these changes, the FAA is considering further rulemaking.”
Boeing does not have a timeframe for when Block Point 5.0 will be ready.
“We’re working with the FAA and our supplier to accelerate a 5.0 version with additional enhancements,” the company said. “Once the software modifications are complete it will go through rigorous testing to ensure it operates as intended.”
Meanwhile, Boeing is working with operators to mitigate risks while it develops the new software version. It issued a multi-operator message in October 2019 explaining the issue to operators and highlighting “existing procedures to safely use alternate navigation systems on the airplane, as outlined in the flight crew operations manual,” the company said.
“We are continuing to hold regular calls with operators to discuss flight crew procedures that Boeing recommends and keep them informed of the progress we’re making,” Boeing said.
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