Tindi Cracked Windsheild Question

['CauseTheCaravanCan]

Thread gone too soon.
Mods don't you know how close to Christmas it is? I didn't have the spare time to get on here and comment before the thread was already locked!

My question IS:

I once heard about some airplane falling out of the sky due to a bird through the windscreen creating a large enough hole, that the aircraft was unable to overcome the drag of the windshield hole.
Maybe these guys heard the same story and figured they had better A) not continue running heat (fire blah blah, B) scrape an already fragile windscreen, or C) wasting the time bombing around trying to scrape it at all, just incase the crack got worse, and fragmented and (well you can imagine the worst case scenario I guess).

Anyways, I still think this is noteworthy, because we aren't JUST talking about a no vis. landing. We're talking about damage to a surface largely resposible for smooth airflow over the cabin, and the ensuing split second decisions I'm sure these guys figured they had to make.

I feel like it turned out really well for them.

Great job Tindi Crew!

[oldtimer]

One item most people seem to forget is that the heated windshield in a pressurized airplane is actually in 3 layers. There is the outer glass portion, the inner viynle layer, oft refered to as the "bird bag" and the inner glass portion. Break the outer layer and the other two still have structural integrety. From the sounds of it, the inner portion broke because it breaks into crumbles so there are no sharp edges. It has been my experience, (Beech 350) that if the outer layer breaks, the glass will crack like an auto windshield but the inner layer will crumble like the side or rear windows in a car. The electric heating element can short out, usually where it attaches to the window, and smake and fire will result but will cease as soon as windshield heat is turned off. Scared the crap out of me when it happened in a Beech 200. The AFM in every pressurized airplane I ahve ever flown states that a cracked windshield will still retain structural integrety. the only time I have ever heard of a bird coming through the windshield is in a non pressurized airplane with thinner glass or plexiglass windshields.

[Brown Bear]

"unable to overcome the drag of the windshield hole....."
Okay, I had a loon come through the windshield of a 310. There is no drag. A bit of a draft, but drag is countered by the back pressure of the air coming in. If the airplane in the "legend" came down, it wasn't due to the drag caused by the hole. After our windshield was holed, we landed, removed most of the right side of the windshield to prevent cracked pieces of plexiglass from coming off in flight.....then took off and flew to our base. It was actually no big.

[GyvAir]

I googled around a bit and came up with a couple documented cases of light singles not being able to maintain altitude after catching a bird through the windshield. I imagine most larger, more amply powered aircraft would be more than capable of overcoming any added drag associated with a broken windshied, especially a Dash 7.

Maybe it was actually the extra weight of the bird laying in the pilot's lap in this case?:

[pelmet]

Thread gone too soon.
Mods don't you know how close to Christmas it is? I didn't have the spare time to get on here and comment before the thread was already locked!

My question IS:

I once heard about some airplane falling out of the sky due to a bird through the windscreen creating a large enough hole, that the aircraft was unable to overcome the drag of the windshield hole.
Maybe these guys heard the same story and figured they had better A) not continue running heat (fire blah blah, B) scrape an already fragile windscreen, or C) wasting the time bombing around trying to scrape it at all, just incase the crack got worse, and fragmented and (well you can imagine the worst case scenario I guess).

Anyways, I still think this is noteworthy, because we aren't JUST talking about a no vis. landing. We're talking about damage to a surface largely resposible for smooth airflow over the cabin, and the ensuing split second decisions I'm sure these guys figured they had to make.

I feel like it turned out really well for them.

Great job Tindi Crew!

Cracked windshields happen. In my experience, for three-pane windshields, usually the outer pane does not affect pressurization requirements(in my experience). Inner one usually does. It is standard for the heat to be turned off. I don't know if the Dash-7 has both front windows on the same circuit or not. If so, then no heating at all. Standard consideration in the case of no heat for either windshield would be to go somewhere with no icing. If that is not possible, an ILS back in YZF makes sense to me. Windshield air heat may be available for some aircraft but several factors would determine how effective that would be.

I have no idea what the weather was like at other airports that day within their range.

I don't remember any airliner ever losing a properly installed windshield due to cracking so not a consideration except for slower airspeeds flown in case of a birdstrike. Scraping a cracked pane of this type is not a worry even if it was an inner pane, except.....never use you bare hand on a cracked pane(at least don't slide your hand across the crack). Even to check if it is the inner, middle or outer that is cracked, you should use a fingernail on the crack or place an object on the window adjacent to the crack such as your pen to see which layer has the crack.

[Brown Bear]

Good point Pelmet. The thought of sliding your hand over a cracked inner pane, hurts!

[Pavese]

I googled around a bit and came up with a couple documented cases of light singles not being able to maintain altitude after catching a bird through the windshield.

I can add another report for a high wing light single. A friend with a Murphy Rebel homebuilt (O-320) had a windshield fail (blew in on him), he reported it became hard to control and could not maintain level flight. His best place to put it down was a beach, apparently he had about 20 miles to "choose from".

He said he drew on the advice of Bob Hoover who apparently said that if you're going to crash, fly the plane as far into the crash as you can and you've got a good chance of walking away and Rick did indeed walk away.

There's a good interview with him at the scene and photos on this site: http://blogs.abc.net.au/nsw/2010/04/eme ... tells.html.

D

[shimmydampner]

From an older thread, some words of wisdom from an esteemed poster:

Please, please respect electrical malfunctions. They can kill you. Think twice before resetting a circuit breaker in flight, unless you really really really need that system. As BPF says, with smoke in the cockpit get the master off and land NOW. Don't worry about ATC getting it's panties in a bunch - just declare an emergency, tell them what you are going to do and turn the master off.

[J31]

From an older thread, some words of wisdom from an esteemed poster:

Please, please respect electrical malfunctions. They can kill you. Think twice before resetting a circuit breaker in flight, unless you really really really need that system. As BPF says, with smoke in the cockpit get the master off and land NOW. Don't worry about ATC getting it's panties in a bunch - just declare an emergency, tell them what you are going to do and turn the master off.

Good advice as a electrical fire can get catastrophic very fast.

This will work in say a late model Cessna 172 where loss of flap extension will have very little effect on an emergency landing.

However electrical malfunctions need to be dealt with according to the aircraft manufactures recommendations. Removing all power in many aircraft will eliminate many essential systems including instrumentation and flight controls. Many aircraft have emergency procedures to isolate electrical problems but the common theme is unless the fire is confirmed out, land ASAP.

Know your aircraft, systems, and recommended emergency procedures. Train to deal with emergencies.

[Siddley Hawker]

Here's the generic shit on aircraft windshield heat, Oldtimer has already covered the windshield makeup. Aircraft windshields are heated for two reasons, the obvious one for anti/deice, and for bird strike protection. If a heated panel shorts out or begins to arc, the procedure is to turn that panel off, thus both anti/deice and bird strike protection is lost. There are airspeed and temperature limitations that must be observed in this case. Cracking of a windshield panel is also cause to turn off the heat, with the added procedure of depressurizing the airplane to some value less than max, usually one psi differential. Hot air defrosting would be still available, but depending on the source - either Janitrol or bleed air - defrosting is wishful thinking, defogging would be more like it. The best defrosting used to be the elephant's pecker in the old DC days.

[lownslow]

Aircraft windshields are heated for two reasons, the obvious one for anti/deice, and for bird strike protection.

I've heard that before but with no real explanation. Am I to believe that warming up the windscreen by a few degrees is going to soften it enough so birds just sort of bounce off or is there something else at work here?

LnS.

[pelmet]

Apparently it makes a difference. And I think it is warmed up more than a few degrees. If the OAT is -30 but your windshield is nice and warm to the touch, there will be a difference.

[lownslow]

Apparently it makes a difference. And I think it is warmed up more than a few degrees. If the OAT is -30 but your windshield is nice and warm to the touch, there will be a difference.

I may have under exaggerated the temp change but I still would have expected the heating to be pushing a thousand degrees to make any real difference. As always, I reserve the right to be wrong on this.

LnS.

[oldtimer]

I am thinking a lot is genaric in nature but most heated windshields I have encountered have thermostats that try to keep portions of the windshield at approx. 100 degrees F. Glass is supposed to be 5 times stronger when warm.
From the posts, it appears that there are a number of pilots thinking small airplane systems but there is a big difference between FAR Part 23 airplanes and Part 25 Transport Category airplanes such as the -7. With small airplanes (12,500 MTOW or less) there is no requirement for the windshield to be bird proof so if a large bird hits the windshield, it will most likely go through with unknown consequences. With small turbine airplanes, again there is no requirement as far a I know but they try to follow the standards of large airplanes such as the "bird bag", heated windshields and glass that is both curved and sloped so a bird cannot hit the windshield dead on, only a glancing blow.
Also, all turbine powered airplanes have the electrical systems divided into many busses so a short or failure in one system will not bring down the whole aircraft system. The Metro for example has the power distribution divided into 3 busses, each with a bus tie switch which will isolate only the malfunctioning bus so all 3 are not taken down.
I also believe the -7 has at least 4 windshields, two facing the pilots and 2 at an angle plus the 2 side windows.
Years ago, Time Air bought the forward section of a crashed F28 fuselage (From New York) to use the doors as a training aid for flight attendents. The windshield was removed but still in its frame so they got the fire department in with their crash axe to try to bust through the window. They were not sucessful. I got a piece of plastic cut from an unservicable Lear Jet windshield and it was about 2 inches thick.
it is nice to see people asking questions , that is how you learn.

[Brown Bear]

Aircraft windshields are heated for two reasons, the obvious one for anti/deice, and for bird strike protection.

I've heard that before but with no real explanation. Am I to believe that warming up the windscreen by a few degrees is going to soften it enough so birds just sort of bounce off or is there something else at work here?

LnS.

Think of a piece of toffee (I love that stuff) fresh out of the fridge. Now, slam it on a table. Instant bite size pieces. Yum. Now, just try to break off a piece at room temperature. No way. It just stretches. Same with your windshield. Cold=Brittle. It's that simple.

['CauseTheCaravanCan]

I find myself very satisfied with these answers. I had no idea about the triple pane and "bird bag". Gotta get me one of those.

[flyinthebug]

Think of a piece of toffee (I love that stuff) fresh out of the fridge. Now, slam it on a table. Instant bite size pieces. Yum. Now, just try to break off a piece at room temperature. No way. It just stretches. Same with your windshield. Cold=Brittle. It's that simple.

Best explanation I`ve heard. Perfect example.

[xsbank]

Once upon a time, a Challenger jet crashed on takeoff at Witchita, during a test flight. It caught fire. The firemen were there almost immediately and set about trying to chop through the windshield, because they could see the crew alive inside just under it.

They failed. Never opened a slot larger than you could post a letter through (a what?) even whaling on it with fire axes. The crew perished.

A windshield is never an exit; all the speed limitations below 10,000' on faster aircraft are not for the regulations, but for bird strikes. Also, I think somebody else mentioned that there are usually speed limitations for windshield heat failures too.

A propos nothing, the heated windshields are frequently the single largest electrical load on many aircraft.

[CID]

Windshields in pressurized aircraft can be made from several layers, sometimes much more than 3. The Kingair series actually use urethane as one of the layers - not all glass.

FAR 23 does in fact have a requirement to address flight into known icing and commuter category aircraft under FAR 23 have a bird strike requirement to withstand a 2 pound bird at maximum approach speed. And that is regardless of whether the aircraft is pressurized.

Although not explicitly stated, the windshield standards cause manufactures to heat windshield panels. They do that to meet the strength requirements. Depending on how you read and interpret the standards, windshield heat is used primarily for material strength requirements (not just bird strikes) and secondarily to keep the frost off. As was mentioned before, inop windshield heat on high performance pressurized aircraft imposes airspeed limitations.

The toffee example was good to demonstrate how materials become brittle when cold but do we really need to leave the airplane and look at candy to see examples of things that break more easily in the cold?

Last but not least, I really don't think it's a good idea to take off in an airplane with a windshield that is compromised to the point you can pass a bird through it. I certainly hope those statements don't cause anyone to actually try it.

[Colonel Sanders]

http://www.ntsb.gov/investigations/summary/AAR0901.html

http://en.wikipedia.org/wiki/Air_Canada_Flight_797

http://en.wikipedia.org/wiki/Swissair_Flight_111

http://www.nationair-canada.com/crash.html