A "simple, bolted joint" is the culprit for the latest, one-year delay to certificating the Honda Aircraft HA-420 HondaJet, the engine supplier says.

GE Honda Aero Engines, the joint venture that is building the HF120 turbofan, hoped to complete a critical test in December 2012 to keep the HondaJet on track to reach certification in late 2013.

However, with the engine about 25% through a 150h endurance test required for certification, the bolted joint within the accessory gearbox "encountered an issue", says Terry Sharp, president of GE Honda Aero Engines.

The event surprised Sharp's engineering team. Somehow, a latent fault in an accessory system had slipped through undetected after nearly 7,000h of testing on the overall HF120 engine.

 HondaJet HA-420

 HondaJet

It was only noticed, GE Honda officials believe, because the 150h endurance test includes a requirement to artificially heat the oil to higher than normal temperatures, causing more stress on a joint deep inside the gearbox system. "It's an extremely strenuous test for any engine to pass," he says.

The HF120 team was encouraged that the problem occurred outside the core of the engine's turbomachinery, where a design issue could require a more complicated solution.

"We found that actually the corrective action is really quite simple," Sharp says. "It's a matter of changing minor aspects of our assembly process as well as some minor design changes."

However, GE Honda Aero Engines executives had to decide whether to resume testing from the point of the bolted joint failure and restart the test from the beginning.

The inspection "required we had to tear into the engine fairly deep", Sharp says. "Once we opened the engine up, we decided it was better for us to rebuild the engine as a new engine and completely re-run the block test."

The HF120 is now scheduled to be certificated in late 2013, if it clears a final medium birdstrike test scheduled for July. Certification of the HondaJet is now scheduled for late 2014, about one year later than planned.

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Source: Flight Daily News

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