Fatal Crash Patrol N964RS

[Ed.Meyer]

I just learned that. So, apparently a significant negative g event for reasons we will probably never know.

[Nev]

Ed.Meyer I initially thought the same, but after viewing a Patrol skylight I realized that it wouldn't need to be a significant negative G event. It only needs to be enough negative G to float the pilot out of the seat and break the skylight or the skylight attachment points. In my mind that's entirely possible. I am still curious (from a maintenance and learning standpoint) what the yaw issue was that they were investigating, but I expect that might have been mostly unrelated.

[jaredyates]

Bob told me on the phone that he calculates a polycarbonate skylight with screws and backing strips to be capable of holding thousands of pounds. The accident aircraft had an acrylic panel. This is one link in the accident chain.

[Battson]

Agree.

That said. I have stood on my acrylic skylight while the plane was upside down and resting on river rocks. It held up fine. So they can take some weight if carefully applied.

But they are prone to cracking upon impact, especially
- impact with a sharp object
- if the holes have any sharp edges
- builder selected a material too thin for the task

[Nev]

Bob told me on the phone that he calculates a polycarbonate skylight with screws and backing strips to be capable of holding thousands of pounds. The accident aircraft had an acrylic panel. This is one link in the accident chain.

To add a data point here, I installed two polycarbonate skylights on my Bearhawk and both failed due to chemical crazing within a day. I was using Loctite Blue on the fasteners (the Loctite was not touching - it seemed to only need to be proximate), however Avgas will have a similar effect. It was a very expensive exercise. I reverted to Acrylic for the final version with good results so far after 400 hours. My understanding is that Polycarbonate can be purchased with a chemical resistant coating on it. If that were available to a builder then it'd be an easy choice. But the often quoted "250 times stronger that glass" comes with a significant caveat if you have any sort of chemicals around it.

[fairchild1934]

He went out the top ? I have to say I didnt see that one coming !....
i know acrylic is pretty brittle when you push it hard enough to break it. Perhaps it was only 1/8 inch or so.
note to self--- make from lexan or thicker acrylic........ But seems like it would take a lot of g force to send him all the way out----
perhaps what started as a small - maybe inadvertent- stick movement lifted him out of the seat a few inches and that somehow caused the stick to be pushed further forward which induced more negative g. Like a feedback loop ---

t