Small maillon failure

Steve Purdie's picture

The small quick link (copy of a maillon-rapide) securing the lines to the risers on a Paramania glider failed during the test flight of a new wing.

The wing was produced at the Gin factory, so a number of different brands could be affected. (Gin gliders appear to use the real deal)

Do check that your are stamped or engraved with the EN number.

http://paramotorcentral.org/viewtopic.php?f=7&t=31947&p=36703

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Carlo Borsattino's picture

Make sure your Maillons are correctly fastened.

Looking at the photo...
http://paramotorcentral.org/download/file.php?id=21&sid=2ccecc389eef8bc9...
... It looks like the Maillon (metal quick link) has been over-tightened as the metal sleeve has come off the wrong end (the metal sleeve should be attached to the bottom of the Maillon, not the top).

So it seems to me that this incident is most likely caused by someone over-tightening the Maillon, and so damaging the thread, which is a well-known way to make any Maillon fail.

Paramania have issued the following general safety notice regarding the proper use of Maillons:
“Warning: If a person uses a higher force then approximately 0.7Nm which is only 0.51 ft/lbs when closing the maillon, even though there is a stop at the end of the threads, it is possible to over-tighten the nut above the top of the threads freeing the lower part of the screw thread. If this is done it is likely that the lower part of the screw thread will not connect correctly with the nut and the maillon can bend open under load.”

It's good to be prepared, and it is easy to check if you're concerned abgout your Maillons: You can undo and refasten your Maillons correctly (or get an approved service centre like The Loft to do it for you). If a Stainless Steel Maillon is done up so that the threads aren't visible and it is correctly "nipped" with a spanner (not over-tightened!), then it should not suddenly fail.

Carlo Borsattino

The FLYBUBBLE PARAGLIDING team

www.flybubble.co.uk

Advance, Aircotec, Airwave, Brauniger, Charly, Compass, Digifly, Flytec, Flymaster, Gin, Icaro, Kortel, Lazer, Niviuk, Nova, Ozone, Plusmax, Skyline, Skywalk, Sup’Air & Woody Valley

Steve Purdie's picture

Over-tightening

Maillons can indeed be damaged by over-tightening.

Genuine Peguet Maillon Rapides have tightening torques as follow:

Ø F (mm) Couple (N/m)
2,5 0,15
3,0 0,30
3,5 0,60
4,0 0,70
5,0 0,80
6,0 1,20
7,0 2,50
8,0 3,00
9,0 4,50
10,0 7,00
12,0 9,00
14,0 12,00
16,0 18,00
18,0 30,00
20,0 40,00

The failed connector was not a genuine Maillon Rapdie, nor seemingly one manufactured by Gin's usual supplier. It was a 4 mm, which as a Peguet would have a tightening torque of 0.7 Nm, ~0.5 lbf, i.e. only very slightly more than finger tight. It was purportedly not tampered with post manufacture of the wing.

The failure mode of the connector in question is a matter of some dispute and is being investigated by the AAIB. Initial inspection by a BHPA CFI found poor thread forming and that over-tightening damage was not the cause, but this may be revised by the AAIB.

In the past I have experienced more than one instance of worn &/or poor quality fake main maillons opening in flight by simply pulling open... (before carabiners became popular and NOT within Airworks I hasten to add!) Don't use quick links in an application where you intend to repeatedly open them, especially in the smaller (less than 10mm) sizes.

If a number of threads are visible at the top when the fitting is closed then it has probably sprung and is closing cross-threaded. This is a separate issue, but must be resolved before flight.

TTFN
SteveP

----------------------------------
AIRWORKS PARAGLIDING & HANG GLIDING
The Old Station
Glynde
BN8 6SS

info@airworks.co.uk
www.airworks.co.uk

Advance, Aircotec, Aircross, Airwave, Ascent, Brauniger, Charly, Digifly, Firebird, Flytec, Flymaster, Gin, GoPro, Independence, Kannad, Kortel, Lazer, MemoryMap, Niviuk, Nova, Ozone, Peguet, Plusmax, Pro-Design, Skyline, Skywalk, Spot, Sup’Air, Swing, Yaesu & Woody Valley

Steve Purdie's picture

Further information

Hello Steve,
just saw your website safety advisory and wanted to give you an update. It appears that the failed maillon is not made by Gin. Gin maillons can be identified by having no markings whatsoever but have plastic insert line keepers and are 4.3mm I think. I do not think that Gin gliders are affected, but only some Paramania ones if they have the 3.5mm maillons with 316 stamped on the long side and rubber O ring line keepers.
Pictures at paramotorcentral.

Kind regards,
Francis