A software bug that shut-down one engine on a GE Aviation-powered 787 last July has prompted Boeing to ask the US Federal Aviation Administration to temporarily exempt the 787-10 from a safety requirement.

Boeing plans to certificate the GEnx-1B-powered version of the 787-10 in September, but the fix for the software bug won’t be ready until 20 December 2019, Boeing says in the filing.

In a separate interview with FlightGlobal, GE says it plans to deliver the software update sooner.

Unless the FAA approves Boeing’s exemption request, the delivery schedule for the GEnx-powered version of the 787-10 could be delayed, Boeing says. Boeing delivered the first Rolls-Royce Trent 1000-TEN-powered 787-10 in March, but the first GEnx-1B-powered version is to be delivered to United Airlines in September.

GE plans to fix the software bug that caused the engine shutdown as part of a package of updates called the “B200” software version, Boeing says. It could deliver the fix that specifically addresses the engine shutdown problem earlier, but Boeing prefers to keep it packaged with several other updates..

The software bug is related to another safety problem with the GEnx-1B.

In certain, rare conditions, tiny ice crystals blown high by atmospheric convection into the stratosphere can form on blades and vanes within the GEnx-1B. R-R’s Trent engine family seems immune from the problem, but accumulated ice crystals in the GEnx engine can shed suddenly, causing an in-flight shutdown.

Two years ago, GE solved that problem by introducing a software modification. If ice crystal icing (ICI) conditions are detected, the software commands the variable inlet guide vanes – a set of interior doors used to discard foreign object debris on takeoff or landing – to open and eject the ice before it can enter the core of the engine.

That fix appears to be working, but Boeing has found a new bug in the software used for opening the doors.

Last July, a 787 crew encountered ICI conditions at 40,000ft, so commanded the engines to provide power for two step climbs up to 42,000ft. During the climb, the left-hand engine flamed-out, causing power to roll back. The engine’s electronic controls recognized the problem and automatically activated the igniters for a relight. The combustor re-lit within 2s and thrust was restored fully within 18s, Boeing says.

“The root cause of this event is the fact that ICI accommodation logic, as it’s currently certified, is suspended with the application of climb power,” Boeing says.

GE’s software update will insert logic to extend ICI protections at engine power levels up to climb at altitudes over 35,000ft, Boeing says.

GE-powered versions of the 787-8 and 787-9 can continue flying under existing airworthiness certificates. The 787-10, however, is still wrapping up certification testing, so the non-compliance presented by the known software plug requires Boeing to request an exemption.

Source: Cirium Dashboard