Windshield cracks and "spider-ing"

[Stetson20]

Buddy flew my plane (Mooney M20K Rocket) yesterday on an Angel Flight mission from east coast of FL to panhandle and back. He said these showed up after flying it. 

Anybody have any experience with this? My A&P is out of town until Monday and I was just looking for more information about Mooneys and windshield cracks. Nothing really in previous threads that I've seen. 

I suspect the crack on the lower windshield is from the new panel install last year, and after the install, another shop had to access behind the panel to fix some gremlins.

Thoughts on whether the cracks are repairable, or a new windshield is warranted? Is it flyable or an airworthiness issue?

Thanks for your thoughts...

Stetson20

 

[N201MKTurbo]

Bummer.

Start planning for a new windshield.

[Stetson20]

7 minutes ago, N201MKTurbo said:

Bummer.

Start planning for a new windshield.

Flyable in the interim? 

[N201MKTurbo]

Just now, Stetson20 said:

Flyable in the interim? 

I've seen worse flying. I wouldn't fly it forever. I would look in the service manual and 4313-1B to see if there is any guidance. 

[0TreeLemur]

How old is it?   Seems odd that it shows up top & bottom at the same time.  Suggests an event (thermal stress, bird strike, or improper cleaning solution like ammonia).  If it were mine I'd want to know more about the cause before flying it again.

[N201MKTurbo]

I just did a web search. If you had a jet or a pressurized airplane, there is a lot of guidance. Not much written about out windshields.

[N201MKTurbo]

The service manual just tells how to replace it. The inspection says to inspect got cracks and crazing. It doesn't give any guidance for any crack limits.

[PT20J]

Acrylic tends to propagate cracks and my concern would be that air loads would cause a sudden catastrophic failure. On the other hand, acrylic solvent welds easily and it might be possible to stop drill and solvent weld it enough to make it safe if you need to ferry it to a place to have the windshield replaced. I might call Great Lakes Aero https://www.glapinc.com/ for advice -- they manufacture the windshields.

[EricJ]

25 minutes ago, N201MKTurbo said:

I just did a web search. If you had a jet or a pressurized airplane, there is a lot of guidance. Not much written about out windshields.

Yeah, we're kind of on our own.    I can't find any guidance in the M20J SMM.   AC 43-13-1B has a good section on repairing transparent plastics, and is pretty general as well.   It says, "Replace, rather than repair extensively damaged transparent plastic, whenever possible, since even a carefully patched part is not the equal of a new section, either optically or structurally.", and, "The following repairs are permissible; however, they are not to be located in the pilot’s line of vision during landing or normal flight."    So if you don't have "extensive damage" or damage in the "pilot's line of vision" it's not going to require replacement.

Repair methods in AC 43-13 are pretty straightforward, although I'd be hesitant to try to stop drill them since windscreens are sometimes laminated and you might wind up doing more damage than good.   There are surface patches that are pretty easy to do that will distribute load and reduce the likelihood of cracks propagating.    I've seen those done on some fast twins and they can look nice and last a long time.    At least, the ones I saw looked like they'd been there for a long, long time.

All that said, mine has had similar cracking at the base of the windscreen since I bought it six-and-a-half years ago.    I just keep an eye on it and it hasn't gotten any worse.   If yours do start to propagate, a surface patch might keep it flyable until you can get a replacement.

EDIT:   I should have included the relevant section of AC 43.13 is 3-24.

[N201MKTurbo]

In the end, it is the operator who determines if the airplane is airworthy. The IA just inspects it. That being said, that windshield is ugly! Who wants to fly around with that? 
 

As far as safety is concerned, I wouldn’t worry about it, but I would keep an eye on it. If those cracks start to grow, I would accelerate your replacement schedule.

[ArtVandelay]

In the end, it is the operator who determines if the airplane is airworthy. The IA just inspects it. That being said, that windshield is ugly! Who wants to fly around with that? 
 
As far as safety is concerned, I wouldn’t worry about it, but I would keep an eye on it. If those cracks start to grow, I would accelerate your replacement schedule.

I would replace with the thicker glass if you don’t already have it.

[A64Pilot]

I’ve drilled a row of holes on either side of a side window crack on Military helicopters and sewed it with copper safety wire and glued it as a temporary fix, but that was a side window, and we almost always flew with the doors off anyway.

In my opinion that’s not airworthy, besides the real possibility of getting a windshield in your face when one let’s go the increase in drag is phenomenal so much so that depending on gross weight density altitude etc continued flight may not be possible. I’ve see a 152 that couldn’t fly after a bird strike took out the windshield, landed in a cow pasture, no damages or injury but it wouldn’t fly, almost but couldn’t maintain level flight

I’m real sure if a FSDO inspector sees that he’s red tagging your airplane.

Not trying to disrespect your friend, but I think something happened, I’d at least do a hard landing inspection, to me that looks stress induced

Top AND bottom cracks at the same time?

[ArtVandelay]

Not trying to disrespect your friend, but I think something happened, I’d at least do a hard landing inspection, to me that looks stress induced
Top AND bottom cracks at the same time?

I would think a hard nose landing or severe turbulence could cause it.

[Shadrach]

29 minutes ago, ArtVandelay said:

I would think a hard nose landing or severe turbulence could cause it.

Perhaps, but I don’t think the plane would be reusable after such trauma. Remember that the wings and nose gear attach directly to the steel substructure. The windows are glued and screwed to the aluminum skin. Any energy transfer sufficient to crack a window would likely cause significant deformation of the skin to which it’s anchored.

[EricJ]

I was thinking either a bird strike, or somebody bonked it pretty hard from the inside somehow.    The ones on the roof may have been from somebody leaning on the roof too hard, maybe?   Regardless, I agree that something likely caused those, but it could have been a lot of things.    Whatever it was I think it was probably significant.

[Shadrach]

19 hours ago, 0TreeLemur said:

How old is it?   Seems odd that it shows up top & bottom at the same time.  Suggests an event (thermal stress, bird strike, or improper cleaning solution like ammonia).  If it were mine I'd want to know more about the cause before flying it again.

Ammonia did not do this...  Agree that it looks like a physical event precipitated the damage. I can’t imagine a natural thermal event would cause this. All of the flights in the last month were well below 10K. I would not rule out vandalism. A hammer fist hit to the center of the windshield might cause this kind of damage.

[A64Pilot]

1 hour ago, Shadrach said:

Perhaps, but I don’t think the plane would be reusable after such trauma. Remember that the wings and nose gear attach directly to the steel substructure. The windows are glued and screwed to the aluminum skin. Any energy transfer sufficient to crack a window would likely cause significant deformation of the skin to which it’s anchored.

You would be surprised, take a ride in most smaller Cessna’s, if they don’t have the seaplane brace the squeaking you hear taxing is the windshield moving in the frame, it’s surrounded by felt to allow the airframe to flex without stressing the windshield. Google “Cessna windshield squeak”. Airframes flex more than we think, especially tube steel ones. Cessna floats the windshield because if they didn’t it breaks. 

Acrylic is very flexible, but as it ages it gets brittle.

My contention is “something” broke that windshield, usually you can see damage at the impact point if something impacted it, if you rule out an impact what’s left?

If it were mine I’d look for hard landing damage, what can looking hurt? At least ask the pilot when it broke.

[Utah20Gflyer]

I have a few cracks smaller than the ones depicted that haven’t grown in several years.  At the moment they don’t concern me and my IA hasn’t had an issue with them.  So until something changes I don’t intend to do anything.  
 

The cracks depicted are a little concerning.  I wouldn’t expect a catastrophic failure but I would start planning on a replacement when convenient.  I’d order a windshield, find a shop to schedule me in and feel just fine flying it to the shop when the time came.  
 

I’ve never heard of a cracked windshield imploding with out a bird being involved.  I could just be unaware but I don’t think that’s a thing.  

[Shadrach]

2 hours ago, A64Pilot said:

You would be surprised, take a ride in most smaller Cessna’s, if they don’t have the seaplane brace the squeaking you hear taxing is the windshield moving in the frame, it’s surrounded by felt to allow the airframe to flex without stressing the windshield. Google “Cessna windshield squeak”. Airframes flex more than we think, especially tube steel ones. Cessna floats the windshield because if they didn’t it breaks. 

Acrylic is very flexible, but as it ages it gets brittle.

My contention is “something” broke that windshield, usually you can see damage at the impact point if something impacted it, if you rule out an impact what’s left?

If it were mine I’d look for hard landing damage, what can looking hurt? At least ask the pilot when it broke.

I agree something broke it. However, given what I know about the construction of the Mooney airframe, it seems highly unlikely this was transmitted through the steel frame to non structural aluminum sheets then through the retainers and the adhesive to the plexiglass.  I don’t believe it likely that it was airframe “flex” from a flying/landing event unless there is additional damage that we can’t see. Looks like someone whacked it with something. Maybe there were some kids playing soccer on the ramp and the ball got away from them…

[A64Pilot]

I would get one from LP aero, get the grey tinted one, not the green and for sure the thicker one, because the thicker one reduces noise by quite a bit

[Stetson20]

The crack at the bottom of the windshield- I'm fairly certain it happened sometime during the installation of the new avionics and front panel. I didn't catch it so it's on me. The top cracks are very small and almost not noticeable. I put my hand in the frame for reference. 

 

[Gary0747]

Those cracks look pretty big but for smaller cracks, there are a few solvents that work well for bonding acrylic.  Methylene Chloride, Ethylene Dichloride and Methyl Ethyl Keytone come to mind.   One could put some in a a glass eye dropper and see if it will weep into the cracks.   

[DCarlton]

I’ve heard there can be fitment issues with the thicker glass option.  Has anyone experienced problems during install?  Considering a new windscreen too.  
 

[A64Pilot]

5 hours ago, DCarlton said:

I’ve heard there can be fitment issues with the thicker glass option.  Has anyone experienced problems during install?  Considering a new windscreen too.  
 

It is more work at least on a Maule which is my only experience but it is do-able and worth the results.

Put your hand on the windshield while in flight, you may be surprised at how much it vibrates, those vibrations of course are like a big speaker cone moving, they make noise, reduce the vibes and obviously the noise is reduced. Thicker / stiffer windshield doesn’t vibrate as much.

It’s my belief that most of the vibrations come from the prop and the reason why a three blade prop is quieter is that it has more frequent but lower amplitude vibrations. I believe most of the noise comes from the windshield. I’ve not tried this experiment but if I’m right if you get a pax to push on the windshield with both hands you should notice a reduction in noise

The thicker windshield in my Maule reduced the noise by as much or more than the three blade prop did, was cheaper and didn’t come with a performance hit the three baked prop did.