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Proposed AD for PA-28 wing spars

I cropped the logbook a bit to remove the signatures

Administrator
Shoreham EGKA, United Kingdom

IBRA

The Robin AD is particularly badly written with total hours being the governing factor so a glider tug will make between 5 & 6 landings an hour, a Touring Robin like mine that was going UK to South of France was at about 0.75 landings an hour so the touring aircraft is vastly over maintained . ( But my long range mission is not typical of Robins generally with I would guess 1.5 landings / hour being typical )

The definition of Grass Vs hard surface is a bit harder to make work as some grass airfields are very smooth and others like White Waltham resemble ploughed fields

A_and_C wrote:

The Robin AD is particularly badly written with total hours being the governing factor

Yes, that PA28 AD formula has something that relates to the number of cycles, something very useful to factor in the operating hours number anytime we are talking about crack propagation (aluminum or nickel/titanium alloys)

ESSEX, United Kingdom

Dimme wrote:

First I thought your logbook was Swedish until i paid closer attention to the airports. Danish sounds like a mess but written is actually very similar to Swedish.

Well, it is said that Danes, Norwegians and Swedes all speak the same language, but the Danes can’t pronounce it, the Swedes can’t spell it and the Norwegians can’t decide on what it is.

ESKC (Uppsala/Sundbro), Sweden

Ibra wrote:

Yes, that PA28 AD formula has something that relates to the number of cycles, something very useful to factor in the operating hours number anytime we are talking about crack propagation (aluminum or nickel/titanium alloys)

Indeed. Landings are recorded for gliders and commercial airplanes. So it’s look odd that they are not recorded for light aircraft. Airbus does its fatigue calcs based on Flight Cycles (FC) and then multiply that by an average flight time to give the flight hour (FH) inspections. It is only to catch the a/c used by some operators on much longer range missions.

Nympsfield, United Kingdom

Ibra wrote:

Where do you log the number of landings in aircraft logbook? or tech logs? Or is it owner logbook?

For N-registered Pipers and similar light aircraft with a Hobbs meter or similar recording device, no logbook of individual flights exists by either regulation or typical owner practice. So I would not expect any FAA A.D. to be directly structured around number of aircraft landings, flights, cycles or similar.

Obviously given a recording device the total number of hours on an airframe can be determined from the last maintenance logbook entry and/or the total on the recording device. That’s all the data that will be available for most airframes.

Last Edited by Silvaire at 11 Jan 14:23

Aveling wrote:

What I really don’t understand is what the 5 bolts in series actually do. Since all the load is handled by the end bolt, what are the rest actually for?

This is a spliced beam/spar rather than one section of the wing being mounted to another section by using bolts acting as pins. For the Piper the splice is a normal bolted joint. What the bolts do is to clamp the sections together so hard that the friction between those sections is what holds it together. There are no shear forces on the bolts, only tension. 5 bolts are apparently needed to get enough friction force. Using correct torque on the bots is essential. If too little torque is used, the bolts themselves will take shear forces, and in this case the outer one will take almost all of it. The bolts themselves will have no problem with this, but the forces on the flanges will then be concentrated at the bolts with much higher and different stress than what they are designed for. Using too much torque is also not good, that will also increase the total stress.

Using the bolt as a pin is safer. Then the bolt only take shear forces and the material around the bolt is designed accordingly.

Piper CEO response to FAA about the proposed AD.

https://www.regulations.gov/contentStreamer?documentId=FAA-2018-1046-0079&attachmentNumber=1&contentType=pdf

Local copy

Really interesting to read.

Last Edited by By9468840 at 18 Jan 13:34
EDTG, Germany, Switzerland

You just beat me to it, was about to post the same link.

Very interesting as I (and lots of other people) had assumed Piper was working with the NTSB closely on this. Obviously not the case.

United Kingdom

Archer-181 wrote:

Very interesting as I (and lots of other people) had assumed Piper was working with the NTSB closely on this. Obviously not the case.

Isn’t this the case anytime something come up after a headline accident, FAA may ground all relevant series until full NTSB findings come out? (irrespective of what constructor thinks of final findings or how AD is communicated)

I don’t think grounding PA28/PA32 series with 40k aircraft in the air and high safety record is something that on the table (tough for new models/series this does happen but on 1k numbers), so an emergency AD seems to make more sense?

For comparison, after an un-contained engine failure on Southwest Airlines in 2018, FAA did issue an emergency AD on CFM56 turbofans in the same manner (constructor lamed FAA on lack of communication as themselves have self-raised a similar SB), I don’t think FAA/constructor waited for NTSB to finish their work but they were both right and the case turns out to be similar to another accident in 2016…as far as constructors/faa disagreements goes, they are usually just about the “lack of communication” and the “AD wording”

Last Edited by Ibra at 18 Jan 14:49
ESSEX, United Kingdom
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