The US Federal Aviation Administration has certificated new engine-control software for the AlliedSignal TFE731-60 which has been developed to correct an auto-ignition, or "lean blowout"-problem identified during early operations on the Dassault Falcon 900EX.
Problems were first reported when Falcon 900EX operators experienced difficulty starting the -60 engine in very cold weather in Alaska and Kansas. AlliedSignal identified software in the digital engine electronic control (DEEC) as the cause of the lean blowout problem and sent its Boeing 720 testbed with a -60 engine for cold-weather trials in February 1997 to test the new software.
The auto-ignition feature in the DEEC works by detecting any deceleration in the engine which is inconsistent with the operating mode at that time. "If N2 [gas generator] dips low, then the DEEC will increase the fuel flow or even begin the start schedule," says business-aviation engineering manager Karl Johnson. The problem was traced to the scheduling of fuel in response to changing core speed at various conditions. "We've basically introduced new software which gives more sophisticated scheduling. We are softening it somewhat with this 'de-spike' logic," he adds.
The software development was given more urgency by a recent in-flight auto-ignition incident, says AlliedSignal, which, following FAA certification, is now sending engineering teams out to all Falcon 900EX operators to upload the new software.
The operation is expected to be completed by the start of the US National Business Aviation Association meeting in Dallas, Texas in late September.
Source: Flight International
