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Fatigue Cracking Inspection


stevo200
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Hi All!

 

I was just wondering in a general sense, what is the regulations regarding fatigue crack inspections for light aircraft?

 

I have had a quick search on CASA but cant see too much.

 

Are the inspection times all based of the manufacturers maintenance schedule or is there an Australian legislation somewhere that states the intervals between inspections?

 

Also any links to information about how exactly they carry out the inspections would be greatly appreciated!

 

Thanks!

 

Steven.

 

 

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Guest Maj Millard

Steven,

 

Fatigue cracking is something that one must always look for during any periodic inspection. A visual check for any cracking is part of Annual, 100 and 50 hourly imspections, and one must always be on the lookout during a daily preflight walkaround.If a particular aircraft has demonstrated that a certain area or areas is prone to it, then usually a Service bulletin is issued requiring a controlled inspection and spelling out when that inspection should be conducted.

 

Fatigue cracking is often associated with vibration so it is common in and around engine bays, propellers hubs and spinners etc. but can also be caused by 'cycles' where a particular item is subjec to the same loads continuously, IE: wing, wing strut or flight control surface or linkage..............Maj....

 

 

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See also http://www.faa.gov/documentLibrary/media/Advisory_Circular/ac23-13A.pdf

 

The FAA introduced the requirement to address fatigue life issues in GA aeroplanes at their initial Type Certification, in FAR 23.572, which was first introduced in 1969, and did not get really specific until 1973, when the FAA published Report AFS-120-73-2. In Australia, fatigue considerations were introduced earlier than this, via ANO 101.22 Appendix 2, which was applied unilaterally to imported aircraft types (as they almost all were) by Airworthiness Directives. Some of these ADs may still be in force, for older types of aircraft. This was done by the Australian Authority, because many overseas Authorities did not address fatigue issues in smaller aircraft at that time; for example, aeroplanes certificated under the old U.S. standard, CAR 3, had no promulgated fatigue lives unless the Australian Authority imposed them via AD. This situation has largely changed by now; most airworthiness authorities do require fatigue issues in the primary structure to be addressed in the original certification - but this is notably missing in the watered-down standards for recreational aircraft, for the most part.

 

So nowadays, the fatigue life aspects for FAR 23 aeroplanes, and others whose certification standard required this, will be found in the "Airworthiness Limitations" section of the aircraft's Approved Maintenance Manual. For older types, check the ADs, both those issued in Australia and those in the country of origin.

 

 

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Get yourself a 50mm round extendable mirror and a good led torch and check as much of the structure [ gain access also thru all removable panels]. If wings are fairly easy to remove do so,as you can then look down to see the spars etc. It really depends on how thorough you need to be [ if you don't have a manufactures manual see other similar aircraft manuals] with respect to time since the last one and hours flown including number of landings.

 

 

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By the time fatigue cracking is visible, it's generally too late - unless the structure is designed to be "damage-tolerant". I do not know of any recreational aircraft that has been certificated as meeting the damage-tolerant criteria. So relying on finding fatigue cracking in critical flight structure as a means of fatigue management is tantamount to a form of Russian Roulette.

 

 

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