Epidemic of cracked windshields in KDEN, explanation unknown

See

http://us.cnn.com/2007/WEATHER/02/17....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.

On Feb 17, 11:15 am, Mxsmanic wrote:
See

http://us.cnn.com/2007/WEATHER/02/17....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

"Kev" wrote in message
ups.com...
On Feb 17, 11:15 am, Mxsmanic wrote:
See

http://us.cnn.com/2007/WEATHER/02/17....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.

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.

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....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 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)

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

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............

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.

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