Check landing gear bolts

[AlexZ]

Check landing gear bolts regularly!
In March we had a mishap during landing. The bolt holding the axle snapped and the wheel rotated. Luckily no nose over. Pffft.

Mishap

We made up a report of the fix.

Damage repair after incident 20240306.pdf

Repair report

(276.88 KiB) Downloaded 248 times

[WaiexB22]

Thanks for sharing! Did you have the AN bolts in or the originally specified stainless? Any photos of the bolt you could share?

[bvolcko38]

I saw this situation developing on my Xenos. This is my fix:

[MichaelFarley56]

I'm a little curious on the damage of the Sonex pictured above. The left axle is obviously broke but how did the damage occur on the right wheel pant? It looks like the wheel pant itself was dragged on the top surface, perhaps by a broken weldment holding the wheel pant bracket in place?

[Kai]

As the originator of the first report to Sonex that resulted in the first edition of service bulletin SNX-SB-006 (I see that it has now been edited and extended somewhat), we had our fair share up here of broken bolts in the undercarriage- but all were the upper bolts fixing the titanium legs to the engine mount. As such, the pictures above had me scratching my head: my first reaction was that there must have been some misalignment- but of course there might very well be other explanations as well.

SNX-SB-006 mandates the replacement of the upper original stainless steel 1/4 in bolts with AN-4 hardware. We have found that these bolts too could very well snap off in the leg without anything visible on the outside, but as long as both halves of the bolt remain inside the leg, the worst of a calamity might be avoided. As such we as a matter of course apply an outside safety wire between bolt head and nut, keeping everything were it should be. True, the leg is no longer as securely fixed as it should be, but the worst of scenarios is avoided. And having once stood the Sonex on its nose after a main gear collapse with a DHC Twin Otter jumper plane hot on my heels on the rollout, I was not particularily interested to repeat this unhappy event: for me flying in all its aspects offers plenty of exitement as long as everything goes according to the book.

Since then we have extended the SB somewhat, reaming out the holes in engine mount and gear leg to 5/16 in (ø8mm), and replaceing the original (now AN-4) bolt with ø5/16 (ø8mm) 12.9 quality capscrews, as well as high strength long nuts. Then the whole assy is torqued to maximum bolt specs. That was back in 2011- everything is still sitting in there as originally intended.

[AlexZ]

I'm a little curious on the damage of the Sonex pictured above. The left axle is obviously broke but how did the damage occur on the right wheel pant? It looks like the wheel pant itself was dragged on the top surface, perhaps by a broken weldment holding the wheel pant bracket in place?

When the left wheel rotated it pulled so hard at the brake cable the right wheel blocked and the weldment at the right axle holding the backplate of the brake broke. The wheel pant is mounted to that plate so it rotated with the brake plate. I think acting as skid now it prevented a nose over and/or ground loop.

[AlexZ]

For the top bolt we're aware of the SNX-SB-006 and have the AN bolts in and we check them every annual inspection by rotating them and see if it's still one piece. When dismantling the bolts showed severe damage and where at the point of snapping. From now on we'll simply replace them at every annual. The same goes for the bottom bolts.

To prevent loosing the gear leg in the event a bolt will break and drop out I've put a disk at the top end. The bolt holding the disk is just long enough to clamp the top bolt in place.

[DCASonex]

Kai, 5/16" bolts, fully torqued, Sounds like what I did way back in 2011, with okay from Kerry at Sonex. No problems despite quite a number of hard landings.

David A.