Eclipse to Modify FADEC Logic to Cure Dead Throttle Problem

In the wake of the June 5, 2008 incident during which a pilot of an Eclipse 500 experienced loss of throttle response during a windshear escape maneuver, Eclipse Aviation announced Tuesday evening that it’s working with Pratt & Whitney Canada (PWC) and FAA to develop and certify an upgrade to the FADEC software that will prevent recurrence of the engine control problem.

Strain-gauge testing at Eclipse indicated that the FADECs could sense a throttle position fault if both throttles were pushed against the stops simultaneously with more than 30 pounds force on each throttle. The excessive force doesn’t cause a mechanical failure of components within the throttle quadrant. Instead, it results in an electronic glitch. Pairs of potentiometers, linked to each throttle, send electrical signals to the FADECs in proportion to throttle lever movement. The FADECs are programmed to detect a throttle position fault if the potentiometers sense more than 75 degrees of throttle lever travel. That can happen if each throttle is pushed forward with more than 30 pounds of force.

If the FADECs detect such a throttle lever position fault, the result is loss of throttle response, accompanied by a L (R) ENG CONTROL FAIL CAS message. Revised AFM procedures published by Eclipse in response to FAA’s emergency AD 2008-13-51 enable pilots to reset throttle lever position sensing in flight by means of shutting down and restarting an engine or pulling and resetting the appropriate engine control electronic circuit breakers. Either remedial action restores normal throttle response, according to the AFM revision.

To decrease the likelihood of such occurrences, Eclipse and PWC are modifying the FADEC software to increase the maximum allowable travel limit of the potentiometers by four degrees to 79 degrees. Reaching the new limit will require pushing each throttle forward with more than 75 pounds of hand force at the same time, 2.5 times the current level of force required to exceed the allowable maximum travel limits of the potentiometers. This will make the FADECs considerably more tolerant of robust throttle handling.

Eclipse and PWC expect to have approval for the FADEC software revision within ten to 12 weeks. No hardware changes will be required. But factory replacements for current-production throttle quadrants that have failed the operational test required by AD 2008-13-51 are in short supply, some operators report.

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Fonte: Flight Safety Informantion 26/06/2008