Epidemic of cracked windshields in KDEN, explanation unknown

[Mxsmanic]

See

http://us.cnn.com/2007/WEATHER/02/17/winter.weather.ap/index.html

So what would cause windshields to crack on many different types of aircraft
at the same time? It wasn't impact or anything like that. The weather was
not exceptional for a Denver winter. Multiple aircraft models from multiple
manufacturers were affected.

--
Transpose mxsmanic and gmail to reach me by e-mail.

[Kev]

On Feb 17, 11:15 am, Mxsmanic > wrote:
> See
>
> http://us.cnn.com/2007/WEATHER/02/17/winter.weather.ap/index.html
>
> So what would cause windshields to crack on many different types of aircraft
> at the same time? It wasn't impact or anything like that. [..]

I don't believe the "wasn't impact" part. I lived in Denver for a
while, and when the winds whip up, stones fly around. Cracked
windshields and dust-storm-scarred paint can be quite common out
there.

Kev

[Matt Barrow[_3_]]

"Kev" > wrote in message
ups.com...
> On Feb 17, 11:15 am, Mxsmanic > wrote:
>> See
>>
>> http://us.cnn.com/2007/WEATHER/02/17/winter.weather.ap/index.html
>>
>> So what would cause windshields to crack on many different types of
>> aircraft
>> at the same time? It wasn't impact or anything like that. [..]
>
> I don't believe the "wasn't impact" part. I lived in Denver for a
> while, and when the winds whip up, stones fly around.

That brought to mind the skit in "Monty Python and the Holy Grail" about
things that will float in water, one of them being small rocks.

[Mxsmanic]

Kev writes:

> I don't believe the "wasn't impact" part. I lived in Denver for a
> while, and when the winds whip up, stones fly around. Cracked
> windshields and dust-storm-scarred paint can be quite common out
> there.

Maybe. The news article implied that impact wasn't involved.

I was thinking of perhaps some sort of incredibly large temperature
differential, but surely no such differential on the ground could compare with
the differences seen at altitude, so that doesn't seem to explain it, either.

I also understood that most of the cracked windshields occurred on the ground;
only a few involved aircraft that were in the air.

I was under the impression that just about nothing could crack an airliner
windshield short of a transonic brick, but I may be wrong. On smaller
aircraft, I don't know. I suppose they have some sort of regular safety glass
for the windshields, but less fancy than that of high-flying jets (?).

--
Transpose mxsmanic and gmail to reach me by e-mail.

[Jim Macklin]

How cold did it get in Denver? Aluminum and plastic have
different contraction rates with cold. Plastic also gets
brittle with cold. Wind flexes wing, which also flexes
fuselages, erg---cracks.



"Matt Barrow" > wrote in message
...
| "Kev" > wrote in message
|
ups.com...
| > On Feb 17, 11:15 am, Mxsmanic >
wrote:
| >> See
| >>
| >>
http://us.cnn.com/2007/WEATHER/02/17/winter.weather.ap/index.html
| >>
| >> So what would cause windshields to crack on many
different types of
| >> aircraft
| >> at the same time? It wasn't impact or anything like
that. [..]
| >
| > I don't believe the "wasn't impact" part. I lived in
Denver for a
| > while, and when the winds whip up, stones fly around.
|
| That brought to mind the skit in "Monty Python and the
Holy Grail" about
| things that will float in water, one of them being small
rocks.
|

[Bob Moore]

Mxsmanic wrote
> I was under the impression that just about nothing could crack an
> airliner windshield short of a transonic brick, but I may be wrong.
> On smaller aircraft, I don't know. I suppose they have some sort of
> regular safety glass for the windshields, but less fancy than that of
> high-flying jets (?).

Of course these jet windshields are heated to provide the middle layer
of plastic with some flexibility to resist shattering in case of a bird
strike at low temps. Should the heating system be turned off and cold-
soaking occur(electrical bus turned off for trouble-shooting perhaps),
Boeing had a procedure for re-heating the windshield at very low temps
to prevent thermal shock from cracking the glass layers. This involved
cycling the power switches ON-OFF at one minute intervals for several
minutes. Sounds to me as if the temps at DEN were quite low and the flight
crews just turned the windshield heat ON and forgot about it.

Just one possibility of course.....

Bob Moore
ATP B-727 B-707
PanAm (retired)

[Kev]

On Feb 17, 5:14 pm, "Jim Macklin"
> wrote:
> How cold did it get in Denver? Aluminum and plastic have
> different contraction rates with cold. Plastic also gets
> brittle with cold. Wind flexes wing, which also flexes
> fuselages, erg---cracks.

Denver is considered "high plains desert", and is actually quite
moderate. Average temperature in February is around 33 degrees. It's
not unusual to get a blizzard, and then be out in short sleeves the
next day. (It'll be around 50 F tomorrow! )

It'd be a heckuva lot colder in many other places, so cold windshield
cracks make no sense, unless they used the wrong heating process as
Bob Moore suggests.

On the other hand, they mentioned 100 mph ground winds, and that means
flying rocks to me. Windshield replacement is a big business out
there due to so much gravel on the roads :)

Kev

[CRaSH]

Kev wrote:
>
> On the other hand, they mentioned 100 mph ground winds, and that means
> flying rocks to me. Windshield replacement is a big business out
> there due to so much gravel on the roads :)
>


A few decades back we toured the s/e part of Australia by car. At the more
rural towns, the first signs you saw were advertisements for windscreen
replacement. Metal screens in front of your windshield (windscreen) and
headlights were a common sight............

[Blanche]

Winds on Thursday & Friday reached over 100 mph in the foothills.
We don't use salt, as a rule, on the roads. Ice slicer and a
combination of fine rocks. Add to this the everyday, run-of-the-mill
rocks and gravel kicked up on the roads, and it's normal to replace
the windshields every 2-4 years (I'm due this year. Last change
was in 2004). Get these winds, a few hefty rocks, and
a new windshield sooner than expected.

KDEN is surrounded by empty fields (for the most part), which means
lots of "stuff" in the area that is kicked up by the winds.

[Blanche]

High winds. Low temps (-15F and up) ==> very cold wind chill factor.

[Roy Smith]

In article >,
"Matt Barrow" > wrote:

> "Kev" > wrote in message
> ups.com...
> > On Feb 17, 11:15 am, Mxsmanic > wrote:
> >> See
> >>
> >> http://us.cnn.com/2007/WEATHER/02/17/winter.weather.ap/index.html
> >>
> >> So what would cause windshields to crack on many different types of
> >> aircraft
> >> at the same time? It wasn't impact or anything like that. [..]
> >
> > I don't believe the "wasn't impact" part. I lived in Denver for a
> > while, and when the winds whip up, stones fly around.
>
> That brought to mind the skit in "Monty Python and the Holy Grail" about
> things that will float in water, one of them being small rocks.

But, ducks also float, and they fly. Airplanes also fly. Therefore,
airplanes are small rocks.

[Matt Whiting]

Jim Macklin wrote:
> How cold did it get in Denver? Aluminum and plastic have
> different contraction rates with cold. Plastic also gets
> brittle with cold. Wind flexes wing, which also flexes
> fuselages, erg---cracks.

It can't be as cold as the jets routinely see above 30,000 feet. I
suspect the wind was carrying stones or ice chunks or something like
that which cracked the windshields.


Matt

[Kev]

On Feb 17, 7:09 pm, Blanche > wrote:
> High winds. Low temps (-15F and up) ==> very cold wind chill factor.

Common misconception. Wind chill only applies to the heat loss of
animals. It does not apply to inanimate objects. The only thing
wind will do to metal, glass, plastic, etc is help cool it faster to
the ambient temperature.

Kev

[James Robinson]

Matt Whiting > wrote:
>
> Jim Macklin wrote:
>>
>> How cold did it get in Denver? Aluminum and plastic have
>> different contraction rates with cold. Plastic also gets
>> brittle with cold. Wind flexes wing, which also flexes
>> fuselages, erg---cracks.
>
> It can't be as cold as the jets routinely see above 30,000 feet. I
> suspect the wind was carrying stones or ice chunks or something like
> that which cracked the windshields.

I suspect the the crews turned on the electric windshield heating without
proper warmup when it was very cold, and the cracks resulted from thermal
stresses in the windows. The cracks were reported to have happened in the
air, where flying rocks would be rare, and not on the ground.

[Mike Young]

"Blanche" > wrote in message
...
> High winds. Low temps (-15F and up) ==> very cold wind chill factor.

I would think that's still balmy and calm compared to the flight levels. I
dunno why they cracked. The airlines also don't know, and they have been
thinking about this much longer than we have.

[Mxsmanic]

Bob Moore writes:

> Of course these jet windshields are heated to provide the middle layer
> of plastic with some flexibility to resist shattering in case of a bird
> strike at low temps. Should the heating system be turned off and cold-
> soaking occur(electrical bus turned off for trouble-shooting perhaps),
> Boeing had a procedure for re-heating the windshield at very low temps
> to prevent thermal shock from cracking the glass layers. This involved
> cycling the power switches ON-OFF at one minute intervals for several
> minutes. Sounds to me as if the temps at DEN were quite low and the flight
> crews just turned the windshield heat ON and forgot about it.
>
> Just one possibility of course.....

It sounds logical. Many models of aircraft were affected, though (and in fact
Boeing wasn't mentioned--if a Boeing windshield cracks, there's a _real_
problem). Mostly those Brazilian planes and some others. Most were on the
ground, not in the air.

--
Transpose mxsmanic and gmail to reach me by e-mail.

[Mxsmanic]

Blanche writes:

> High winds. Low temps (-15F and up) ==> very cold wind chill factor.

Wind chill applies only to people, not things.

--
Transpose mxsmanic and gmail to reach me by e-mail.

[Matt Barrow[_3_]]

"Jim Macklin" > wrote in message
...
> How cold did it get in Denver? Aluminum and plastic have
> different contraction rates with cold. Plastic also gets
> brittle with cold. Wind flexes wing, which also flexes
> fuselages, erg---cracks.
>

Single digits below zero. Nothing.

Certainly not "rocks blowing around".


> | > I don't believe the "wasn't impact" part. I lived in
> Denver for a
> | > while, and when the winds whip up, stones fly around.
> |

[Matt Barrow[_3_]]

"Kev" > wrote in message
ups.com...
> On Feb 17, 5:14 pm, "Jim Macklin"

>
> On the other hand, they mentioned 100 mph ground winds,

Who is "they"?

> and that means
> flying rocks to me.

As those are borderline tornado winds, it's more like regular debris.

--
Matt Barrow
Performance Homes, LLC

[Matt Barrow[_3_]]

"Roy Smith" > wrote in message
...
> In article >,
> "Matt Barrow" > wrote:
>
>> "Kev" > wrote in message
>> ups.com...
>> > On Feb 17, 11:15 am, Mxsmanic > wrote:
>> >> See
>> >>
>> >> http://us.cnn.com/2007/WEATHER/02/17/winter.weather.ap/index.html
>> >>
>> >> So what would cause windshields to crack on many different types of
>> >> aircraft
>> >> at the same time? It wasn't impact or anything like that. [..]
>> >
>> > I don't believe the "wasn't impact" part. I lived in Denver for a
>> > while, and when the winds whip up, stones fly around.
>>
>> That brought to mind the skit in "Monty Python and the Holy Grail" about
>> things that will float in water, one of them being small rocks.
>
> But, ducks also float, and they fly. Airplanes also fly. Therefore,
> airplanes are small rocks.

Tell us how sheep's bladders can be used to predict earthquakes.

[Crash Lander[_1_]]

"CRaSH" > wrote in message
...
>Metal screens in front of your windshield (windscreen) and headlights were
>a common sight............

You never (rarely) see them now days, since the introduction of the
laminated windscreen. The weather is doing silly things though. The last 2
days, we had 38 degrees Celsius, and yet today, we're having 23 degrees
Celsius, and it's raining!
Oz/Crash Lander

[[email protected]]

On Feb 17, 5:07 pm, Blanche > wrote:
> Winds on Thursday & Friday reached over 100 mph in the foothills.
> We don't use salt, as a rule, on the roads. Ice slicer and a
> combination of fine rocks. Add to this the everyday, run-of-the-mill
> rocks and gravel kicked up on the roads, and it's normal to replace
> the windshields every 2-4 years (I'm due this year. Last change
> was in 2004). Get these winds, a few hefty rocks, and
> a new windshield sooner than expected.
>
> KDEN is surrounded by empty fields (for the most part), which means
> lots of "stuff" in the area that is kicked up by the winds.

Boulder is a town just north of Denver, right at the foothills, which
are steep and abrupt.
Sometime in the late 80s or early 90s, a windstorm from the west blew
out nearly all of the front and back auto windshields in a parking
lot. IIRC it wasn't debris, but the wind itself. It gets to howling
there some times.

Probably nothing to do with the current situation, though. I'd have
to think that a wind that strong would also bend the airplanes up a
bit.

[Mike Hunt]

Jim Macklin wrote:

> How cold did it get in Denver? Aluminum and plastic have
> different contraction rates with cold. Plastic also gets
> brittle with cold. Wind flexes wing, which also flexes
> fuselages, erg---cracks.

Wow. Really? Isn't it cold at 40000 feet?

[Noktomezo]

On Feb 18, 10:57 pm, Mike Hunt <postmaster@localhost> wrote:
> Jim Macklin wrote:
> > How cold did it get in Denver? Aluminum and plastic have
> > different contraction rates with cold. Plastic also gets
> > brittle with cold. Wind flexes wing, which also flexes
> > fuselages, erg---cracks.
>
> Wow. Really? Isn't it cold at 40000 feet?

Usually -50.

[Blueskies]

"Noktomezo" > wrote in message oups.com...
: On Feb 18, 10:57 pm, Mike Hunt <postmaster@localhost> wrote:
: > Jim Macklin wrote:
: > > How cold did it get in Denver? Aluminum and plastic have
: > > different contraction rates with cold. Plastic also gets
: > > brittle with cold. Wind flexes wing, which also flexes
: > > fuselages, erg---cracks.
: >
: > Wow. Really? Isn't it cold at 40000 feet?
:
: Usually -50.
:

Does anyone know the type aircraft they are talking about here?

[Mxsmanic]

Blueskies writes:

> Does anyone know the type aircraft they are talking about here?

Some Brazilian commuter aircraft were mentioned; possibly a few others.

--
Transpose mxsmanic and gmail to reach me by e-mail.

[Nobody]

Is it possible that in very cold weather, using some de-icing fluid that is
too hot would cause windshields to crack ?

[Kenny McCormack]

In article >,
Mxsmanic > wrote:
>Blanche writes:
>
>> High winds. Low temps (-15F and up) ==> very cold wind chill factor.
>
>Wind chill applies only to people, not things.

Not just people. Any warm blooded animal.

For that matter, any heat-generating source (object).

[Jose]

> For that matter, any heat-generating source (object).

Are you sure about that? I thought water evaporation had a lot to do
with it.

Jose
--
Humans are pack animals. Above all things, they have a deep need to
follow something, be it a leader, a creed, or a mob. Whosoever fully
understands this holds the world in his hands.
for Email, make the obvious change in the address.

[Tony]

Wind chill has everything to do with how fast heat is lost from
someone at body temperature. It's widely held that the old data,
that's 'wind chill', is not a very accurate measure of the effect of
wind on flesh and there's some work going on for a better measure. The
statement the poster made about any heat-generating object is not
quite complete, I'm sure he meant to remind us that it's related to
the surface temperature of the object, or at least the surface
temperatture in no wind conditions.

Fans in your computer are there to move air mass against hot objects
to carry the heat away, they are trying to create 'wind chill' inside
the computer. You can google 'convective heat loss' or 'forced air
cooling' if you want to explore the subject in more depth.





s Itr has ewverything to do On Feb 21, 9:33 am, Jose
> wrote:
> > For that matter, any heat-generating source (object).
>
> Are you sure about that? I thought water evaporation had a lot to do
> with it.
>
> Jose
> --
> Humans are pack animals. Above all things, they have a deep need to
> follow something, be it a leader, a creed, or a mob. Whosoever fully
> understands this holds the world in his hands.
> for Email, make the obvious change in the address.

[Mike Young]

"Tony" > wrote in message
oups.com...
> Wind chill has everything to do with how fast heat is lost from
> someone at body temperature. It's widely held that the old data,
> that's 'wind chill', is not a very accurate measure of the effect of
> wind on flesh and there's some work going on for a better measure. The
> statement the poster made about any heat-generating object is not
> quite complete, I'm sure he meant to remind us that it's related to
> the surface temperature of the object, or at least the surface
> temperatture in no wind conditions.
>
> Fans in your computer are there to move air mass against hot objects
> to carry the heat away, they are trying to create 'wind chill' inside
> the computer. You can google 'convective heat loss' or 'forced air
> cooling' if you want to explore the subject in more depth.

Googling on "wind chill" nets a different set of results. Notice the human
reference in the following from weather.gov:

[[
Specifically, the new WCT index:

a.. Calculates wind speed at an average height of five feet (typical
height of an adult human face) based on readings from the national standard
height of 33 feet (typical height of an anemometer)
b.. Is based on a human face model
c.. Incorporates modern heat transfer theory (heat loss from the body to
its surroundings, during cold and breezy/windy days)
d.. Lowers the calm wind threshold to 3 mph
e.. Uses a consistent standard for skin tissue resistance
f.. Assumes no impact from the sun (i.e., clear night sky).
]]

[Alan Gerber]

In rec.aviation.piloting Tony > wrote:
> Fans in your computer are there to move air mass against hot objects
> to carry the heat away, they are trying to create 'wind chill' inside
> the computer. You can google 'convective heat loss' or 'forced air
> cooling' if you want to explore the subject in more depth.

That's not what wind chill is about. You need to take into account
evaporative cooling, which has a significant effect.

.... Alan
--
Alan Gerber
PP-ASEL
gerber AT panix DOT com

[Tony]

I don't think so.

The windchill temperature is calculated using the following formula:

Windchill (ºF) = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)

Where: T = Air Temperature (F)
V = Wind Speed (mph)
^ = raised to a power (exponential)

Windchill Temperature is only defined for temperatures at or below 50
degrees F and wind speeds above 3 mph. Bright sunshine may increase
the windchill temperature by 10 to 18 degrees F.



On Feb 22, 2:12 am, Alan Gerber > wrote:
> In rec.aviation.piloting Tony > wrote:
>
> > Fans in your computer are there to move air mass against hot objects
> > to carry the heat away, they are trying to create 'wind chill' inside
> > the computer. You can google 'convective heat loss' or 'forced air
> > cooling' if you want to explore the subject in more depth.
>
> That's not what wind chill is about. You need to take into account
> evaporative cooling, which has a significant effect.
>
> ... Alan
> --
> Alan Gerber
> PP-ASEL
> gerber AT panix DOT com

[Tony]

I need to retreat a little here. The formula I gave looks to be a
curve fit to an empirical data set, and that data may have been
obtained with evaporative losses as a factor. I seem to remember,
however, the experiments were done observing heat loss from plastic
bottles filled with water, the thickness of the plastic offering more
or less the same thermal impedence as does skin.

So, I hereby extinguish the implied flame.

Sorry about that. Now I'm off to slay more meaningful dragons and save
a maiden or two.

CLEAR!



imperical data ting formay be wrong On Feb 22, 2:20 am, "Tony"
> wrote:
> I don't think so.
>
> The windchill temperature is calculated using the following formula:
>
> Windchill (ºF) = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)
>
> Where: T = Air Temperature (F)
> V = Wind Speed (mph)
> ^ = raised to a power (exponential)
>
> Windchill Temperature is only defined for temperatures at or below 50
> degrees F and wind speeds above 3 mph. Bright sunshine may increase
> the windchill temperature by 10 to 18 degrees F.
>
> On Feb 22, 2:12 am, Alan Gerber > wrote:
>
>
>
> > In rec.aviation.piloting Tony > wrote:
>
> > > Fans in your computer are there to move air mass against hot objects
> > > to carry the heat away, they are trying to create 'wind chill' inside
> > > the computer. You can google 'convective heat loss' or 'forced air
> > > cooling' if you want to explore the subject in more depth.
>
> > That's not what wind chill is about. You need to take into account
> > evaporative cooling, which has a significant effect.
>
> > ... Alan
> > --
> > Alan Gerber
> > PP-ASEL
> > gerber AT panix DOT com- Hide quoted text -
>
> - Show quoted text -

[Tony]

I think the newsgroup would be interested in this finding.

"Although windborne debris was at first dismissed as a cause for the
14 cracked aircraft windshields last week at Denver International
Airport, investigators now are saying FOD, or foreign-object debris,
was indeed to blame. Microscopic analysis showed fine particles caused
pitting that in turn caused cracking, NTSB investigator Jennifer
Kaiser told the Denver Post. The runways had been sanded during recent
snowstorms, and it's suspected that the winds, gusting up to 48 mph,
drove the fine sand particles into the windshields. The fractures
affected six passenger jets as they were taking off, seven on the
airport surface, and one at 19,000 feet. The NTSB offered no
explanation regarding that high-altitude incident. Also unexplained
was the apparent lack of damage to any aircraft surfaces other than
windscreens. "The only commonality across aircraft type, operator,
location, time and phase of flight was the wind and weather," Kaiser
told the Post.


groupOn Feb 18, 9:27 pm, wrote:
> On Feb 17, 5:07 pm, Blanche > wrote:
>
> > Winds on Thursday & Friday reached over 100 mph in the foothills.
> > We don't use salt, as a rule, on the roads. Ice slicer and a
> > combination of fine rocks. Add to this the everyday, run-of-the-mill
> > rocks and gravel kicked up on the roads, and it's normal to replace
> > thewindshieldsevery 2-4 years (I'm due this year. Last change
> > was in 2004). Get these winds, a few hefty rocks, and
> > a new windshield sooner than expected.
>
> > KDEN is surrounded by empty fields (for the most part), which means
> > lots of "stuff" in the area that is kicked up by the winds.
>
> Boulder is a town just north ofDenver, right at the foothills, which
> are steep and abrupt.
> Sometime in the late 80s or early 90s, a windstorm from the west blew
> out nearly all of the front and back autowindshieldsin a parking
> lot. IIRC it wasn't debris, but the wind itself. It gets to howling
> there some times.
>
> Probably nothing to do with the current situation, though. I'd have
> to think that a wind that strong would also bend the airplanes up a
> bit.

[Denny]

Where is Richard Feynman when you need him to explain what the
'experts' can't....

denny

[Mxsmanic]

Isn't sanding areas at an airport kind of a bad idea, precisely because sand
could be FOD?

--
Transpose mxsmanic and gmail to reach me by e-mail.