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Jerry_Atrick

Proposed Wing Spar AD for PA28 and PA32 aircraft

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OK, I admit it.. I like - even love permit (RAA) aircraft types. However, I have remained a CoA/Cat A pilot - I like the robust build and how they are in the main forgiving of some pretty solid landings that I sometimes fall prey to. Although having flown a decent variety of these types, I have liked the Piper low wing models as the airframe has the feel of a solidly built, rugged machine (Grumman has a more solid feel; Beech about the same). Although I have flung C150 and 152 aerobats over the skies in the YMMB and YCEM training areas, for some reason, Pipers just felt more solid. And, on the 5th of next month, I have a Single Engine Piston renewal (BFR or whatever it is called now) booked in a PA28 Warrior III, resplendent with its 8.33mhz spaced transceiver, various push buttons over the old rockers and a chunky yoke to boot. 

 

But, I am now questioning the wisdom of my decision: https://www.federalregister.gov/documents/2018/12/21/2018-27577/airworthiness-directives-piper-aircraft-inc-airplanes. An AD looks like coming alive to check on spars of the venerable PA28s (and PA32s) with what in effect will be over 5,000 hours (I think - I will re-read), lest one of the wing folds up at some stage. 

 

So much for the impression of robustness (said somewhat tongue in cheek - as these a/c get a lot of abuse).

 

 

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The formula in the AD means that only aircraft with many thousands of hours and used for training are likely to need inspection. My 6000 hr privately used PA28 will not need it.

 

 

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What a beautiful piece of easily comprehended writing that proposed AD is. And don't you love the inclusion of estimated costs for the various stages of the job? ($US85 = $AU120 today).

 

I bet if CASA wrote up this AD it would sound something like this: 

 

 

 

 

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What I do not get is that a daily inspection involves grabbing the wing tip and checking for any movement ... no way that level of movement in the video built up in one day so either people didn’t know movement was wrong or they just didn’t check.  

 

 

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That video is really scary.

 

The leading edge attachment bolt would have to be removed to allow that movement. Had a look thru ATSB reports for the pa28 in Australia, zero? Structural failures in over 50 years of service, many hours flown by ham fisted students. I would rather fly in a 10,000 hour pa28 (I have) than some RAA types.  

 

 

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I have about 50 hours in a 20,000+ hour PA28 used pretty much exclusively for training it'e entire life. Am I lucky to be alive? Or is this a beat up?

 

 

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Back when Australia had its own certification requirements: http://services.casa.gov.au/airworth/airwd/ADfiles/under/pa-28/PA-28-058.pdf

 

The PA-28 and others with initial certification many years ago (CAR 3 with a smattering of FAR 23 tossed in for later models) in the USA were not required to have any fatigue life assessment. An aluminium structure will suffer metal fatigue just a matter of when and if inspection picks it up.

 

I like my FAR 23 certified aerobatic airplane with its lifed items.

 

 

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AN176 bolts are Close Tolerance bolts with a 3/8" diameter, 24 TPI.   Tool size 9/16" AF. They have a triangle marking on the bolt head. Up to April 1990, these bolts, if steel, were unplated. From then on, they were made with CAD ll plating. Plated bolts have to be replaced with plated bolts. 

 

https://military-fasteners.com/bolts/a_series/AN176-20

 

In his description of the wing at 1:58, is he correct? I thought the spar was to the leading edge of the wing.

 

 

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In his description of the wing at 1:58, is he correct? I thought the spar was to the leading edge of the wing.

 

The main spar is quite rearward to allow the carry through to be located under the rear seat, also good for main gear attachment 

 

 

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The main spar is quite rearward to allow the carry through to be located under the rear seat, also good for main gear attachment 

 

Also allowed for the fuel tanks to be mounted to and forward of the spar. Had spar cap corrosion on one of our Warriors rather difficult to find since it was directly behind the fuel tank. Daffyd  Llewellyn designed a repair scheme for it. I used to worry about the steel to aluminium fittings on the wings but never really found a problem with them.

 

 

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Here's the calculation:

 

Before further flight after completing the action in paragraph (g)(1) of this AD:

 

((g) Review Airplane Maintenance Records and Calculate Factored Service Hours for Each Main Wing Spar (1) Within 30 days after the effective date of this AD, review the airplane maintenance records and determine the number of 100-hour inspections completed on the airplane since new and any record of wing spar replacement(s).

 

calculate the factored service hours for each main wing spar using the following formula:

 

(N x 100) + [T-(N x 100)]/17 = Factored Service Hours,

 

where N is the number of 100-hour inspections

 

and T is the total hours TIS of the airplane.

 

Thereafter, after each annual inspection and 100-hour TIS inspection, recalculate the factored service hours for each main wing spar until the main wing spar has accumulated 5,000 or more factored service hours.

 

It will be interesting to see how CASA rewords this into Australian terms. The way things have been said in the videos, the Americans only do 100 hourly inspections for each 100 hours' TIS, but we would do an equivalent inspection annually. So, for Australia, for an underused aircraft (private ownership low annual usage),do you determine the value of N from the number of annuals since new? Commercially operated aircraft obviously have more thatn one 100 hourly per year.

 

Let's look at a 1968 PA28-180 privately owned. 50 hours per annum TIS. By December 2019, the aircraft will have had 50 annual/100 hourly inspections; N = 50. Its TIS will be 3750 hrs.

 

(50 x 100) + {[3750 - (50 x 100)]/17}

 

= 5000 + {[3750 - 5000]/17}

 

= 5000 - {[1250]/17}

 

= 5000 - 73.529

 

= 5000 - 73.6

 

= 4926.4 Factored Service Hours

 

You have to be careful with the second component of this calculation. it is only the T-(N x 100) that is divided by 17.

 

looks like a lot of the PA28 family will be sitting around doing nothing over the next couple of years while the people doing non-destructive testing catch up with the demand.

 

Looking for a good career: http://www.attar.com.au/?q=node/221

 

 

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