airworthiness: potential for propeller failures
DESCRIPTION
Airworthiness: Potential for Propeller Failures by FAASTTRANSCRIPT
Presented to:
By:
Date:
Federal AviationAdministrationAirworthiness
and/or Operations
Potential for Propeller failure
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Federal AviationAdministration
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Description of Airworthiness Concern
On June 18, 2012, a Piper PA-28-200, had a liberation of about 6” of the tip of one propeller blade.
The event occurred at Peoria Airport in Peoria, IL
The propeller is a 2-bladed aluminum propeller.
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Event Aircraft Just After Landing
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Leading Edge Damage
– The propeller leading edge shows a significant amount of dents and scrapes from impact with small rocks (probably flown out of a gravel strip).
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Fatigue of Cracked Propeller Blade
• There was significant fatigue evident (about 75% of blade showed fatigue damage), and with only a few hundred hours on the propeller, this leads us to believe the propeller was being operated in a resonant mode.
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Fatigue of Cracked Propeller Blade
Dark grey is failure in overload
Shiny silver is cyclic fatigue
Dull grey is crack initiation site
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Cause of Fatigue• There is a known resonant mode with this propeller/engine combination that has it’s highest
level between 2200 and 2250 RPM.
– An AD had been issued, creating an operating restriction range between 2100 and 2350 RPM. – The propeller manufacturer had provided information to operators to avoid operation below 2500 RPM
• The president of the flying club said their pilots have been told to operate at 2500 RPM. However, it is possible they have been flying at the more traditional 2400 RPM to save fuel.
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Probable Event Scenario
• When tested after the event, the airplane’s tachometer was reading 80 rpm higher than actual rotational speed of the propeller.– Tachometer error discovered by NTSB.– If the pilot set the RPM to 2400, then he was
probably operating in the restricted range below 2350 RPM.
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Resonant Mode Evaluation
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Why does this happen?
• Mechanical tachometers can loose their accuracy over time.
• Reports of tachometer errors of 50 rpm are common and they have been seen up to 250 rpm.
• When the tachometer is out of calibration, you can inadvertently operate in a restricted range, subjecting the propeller to vibration that will cause damage.
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What can you do?
• Check with the propeller manufacturer regarding restricted ranges for your propeller/engine combination
• Verify the proper RPM restrictions are accurately marked
• Verify the accuracy of the tachometer readings – and repeat at regular intervals
• Be vigilant in checking the propeller for damage that can initiate a crack
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Federal AviationAdministration
For more information……
• FAA Special Airworthiness Information Bulletin NE-08-21, issued May 14, 2008
• FAA Advisory Circular 20-37E, Aircraft Propeller Maintenance, dated September 9, 2005.
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Taking these actions will help to
ensure that this does not happen to
you!
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Federal AviationAdministration
Updated FAA Contact Information• For General Propeller issues – Jay Turnberg,
Propeller Specialist, Engine and Propeller Directorate, [email protected]
• For Hamilton Sunstrand – Michael Schwetz, Boston ACO, [email protected]
• For Hartzell Propellers – Chris Richards, Chicago ACO, [email protected]
• For Sensenich Propellers (wood) – Gary Wechsler, Atlanta ACO, [email protected]
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Updated FAA Contact Information
• For Sensenich Propellers (metal) – Ron Segall, New York ACO, [email protected]
• For McCauley Propellers – Steven Litke, Wichita ACO, [email protected]
• For Aeroproducts/Pacific – Margaret Langsted, Seattle ACO, [email protected]
• For Tarver – Jonathan Oxman, Los Angeles ACO, [email protected]
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