Jammed canopy latch

[Chris B]

The main canopy latch jammed in the closed position immediately prior to departure on Thursday. Thankfully my friend is not particularly claustrophobic, though it is quite disconcerting being unable to open the main hatch! We taxied back to the hangar and prepared to clamber out the rear, but the vibrations en-route loosened things up enough that the latch finally opened.

For reference, here is a snip from the AMM (r7, 52-10-00, page eight):



The root cause is a press-fit barrel on the canopy locking bolt that worked loose.

Here is a "normal" locking bolt:



Here is the defective locking bolt:



Somehow the barrel worked loose and slipped forward into the PTFE bushing in the canopy frame. This exposes the sharp machined edge of the locking bolt tip, which readily catches on the outside edge of the frame. No reasonable amount of force is going to overcome the problem if this jams. The canopy handle assembly will probably break first.

Removing the canopy handle and rods is a giant PITA. Unscrewing the outer tip might work, but the connecting rod started to twist before the tip worked loose, and the stainless (non-magnetic) barrel was still inside the frame. Attempting to fix the problem while in a steep climb was clearly the start of an NTSB report.
So after a bit of our solution was:

• Remove the canopy completely (requires three people)
• Tip the canopy aft to expose the barrel
• Clean exposed metal surfaces
• Apply Loctite 271 (red)
• With high-quality pliers, firmly force the barrel onto the locking bolt "shoulder"
• Don't use the latch for several hours

Removing the canopy was surprisingly simple (at least with three people), and so far the fix seems to be working fine. But this is one of the seemingly insignificant checks that I will certainly now make during pre-flight! It also makes me more conscious of ensuring that the latch is not in tension during operation. I can't see any other way that the barrel would otherwise come loose.

Chris

[rwtucker]

Wow! Good save Chris and maybe a save for the rest of us.

[Rich]

Was this the left side? Your illustration seems to indicate so.

[Chris B]

Was this the left side? Your illustration seems to indicate so.

Yes. It failed on the left side. But the same locking bolt design is used on both sides, as well as both locking bolts for the rear hatch. This failure at any of the four bolts will leave the respective hatch INOP. Presumably the risk of simultaneous fore/aft bolt failures is pretty remote, and there is always the emergency release for the rear hatch.

Chris

[mdieter]

Thanks for that report. I would have been freaking out.

[Chris B]

The outer barrel recently started to come loose again from the locking pin.

I subsequently learned a few things that might help others here on DAN:

1. Diamond's support was extremely responsive and helpful.
   I should have called them the first time.
2. The pin/barrel interface is a slip fit (0.05 mm gap) retained via adhesive, NOT a press-fit.
3. Loctite 271 (red) is NOT recommended for this application.
4. The correct adhesive is Loctite 638 retaining compound, specifically designed for "the bonding of cylindrical fitting parts." According to the technical data sheet, Loctite 638 reaches full strength even with stainless steel (unlike other anaerobic compounds), and the barrel should be essentially impossible to remove if correctly installed (~10kN/2000lbs shear). So presumably this problem is rare.
5. For canopies with anodized latch handles (mine is 2008), the locking pin is threaded on an M5 rod, secured with Loctite 242 (blue). But since earlier canopies use different methods of securing the locking pin (e.g., set screw), attempting to unscrew the pin might damage the latch mechanism. Definitely call Diamond support if you have any doubt.
6. Diamond recommended Knipex 86 03 250 pliers to remove the locking pin, which gripped extremely well without marring. Roughing-up the pin/barrel finish will apparently lead to destruction of the PTFE insert inside the frame, which is very complicated to replace.
   
7. To remove the locking pin, Diamond recommended protecting the canopy frame while heating the locking pin tip to weaken the Loctite bonds on the threaded rod. But with the Knipex pliers, we were able to easily remove the pin without heat.

Chris

[NBA]

Hi all,

Apologies for reviving a very old discussion.

Does this also pertain to the DV20?

Can this occur in the DV20 as well? If yes, is there an emergency release? If not, what would be an alternative?