Airborne planes' windshields crack in blustery cold

[Airbubba]

Anyone heard of a rash of cracked windshields before?

Excerpts from an article posted on CNN:

Airborne planes' windshields crack in blustery cold
POSTED: 9:15 a.m. EST, February 17, 2007

DENVER, Colorado (AP) -- Airlines were investigating why windshields on at least 13 planes cracked at Denver International Airport as winds of up to 100 mph whipped through the foothills in Colorado.

...SkyWest Airlines reported cracked windshields on eight planes that were taking off or landing Friday as winds gusted up to 50 mph, spokeswoman Marissa Snow said. One plane's windshield cracked while it was airborne.

"Only the outermost layer was affected," Snow said of the windshields, which are made from multiple layers of glass.
SkyWest, a regional carrier for United Airlines, said the planes involved were the Embraer EMB120 Brasilia and Bombardier Canadair Regional Jet, though she did not immediately have numbers.

Two Frontier Airlines Airbus planes had their windshields crack while airborne, while two other windshields cracked while at the gate, airline spokesman Joe Hodas said.
In all instances the planes returned to the airport and/or made it to the gate safely. No emergencies were declared and no injuries were reported.

Hodas said it was unclear whether the high winds were to blame.

"It's not exactly unusual weather for Denver," Hodas said. "We don't know what it is... It's kind of a mystery at this point."

Spokesman Steve Snyder said windshields cracked on several different makes and models of airplanes from several airlines, though he did not immediately know which and how many. None of the pilots reported flying debris, Snyder said.

"Everybody is fairly baffled by it," Snyder said.
At least 55 flights were canceled and others were diverted...

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

[BEagle]

Inadequate pre-heating?

Back in the days of the VC10, it was common knowledge that a cold-soaked aeroplane had to pre-warmed before power on, otherwise there was likely to be a windscreen failure....

[glhcarl]

Marissa Snow of SkyWest Airlines should be informed that only the outer layer of the windshield is glass. Windshields are made of multi layers of acyrlic with a glass overlay. I have seen windshields crack before in extremly cold weather. Usually it is because the crew selects max heat without first selecting a lower setting. Then thermal expansion takes over an the outer glass cracks.

[Airbubba]

Usually it is because the crew selects max heat without first selecting a lower setting.

Don't know about the RJ's but most larger planes are on/off with windshield heat these days as far as I know. I have seen the demo where a well meaning crewmember selects full hot on all the temp controllers on a cold soaked aircraft. The duct trips work on the new planes just like they did on the classics. :)

[ZeBedie]

It's because the military are testing a new ultrasonic weapon in that area.

[alexban]

Any Boeing involved ? No? I thought so....just kidding.:cool:
I doubt any wind can crack a/c windshields,unless has flying rocks ..or ice,maybe..:hmm: ...Even then,I think ,should be higher than 250kt ,as per QRH :E

[bomarc]

I have no special love for front and rear airlines and skyworst...but ...

leave the freaking windshield heat on all the time (except for non routine ops, see checklist) even overnight...

trying to save a few pennies of electricity on the overnight ends up costing you tens of thousands of dollars for windshield replacement.

[Ronald]

On the B757 and B767 the FWD windsheild heat is initially (automatically)applied at a low power setting before the power is increased. This is probably to try and prevent cracking but no idea what other types use this system.

[parabellum]

On the B737-200 series, as Ronald states for 757/767, the control and application of heat is automatic with a 'ramp' voltage being applied, low at first and gradually increasing but automatically, no manual input.

[F900EX]

Guys..

The heat issue is valid, however lets not forget that some of these aircraft were both arriving and departing when the incidents occured.

Very odd if you ask me.

[Trogdor]

I highly doubt that temperature had much to do with this. It has been a lot colder in Denver in the past few weeks and nothing like this happened. Even after a snow storm closed the airport for almost two days where presumably aircraft sat on the ramp with no heat there were no reports of cracks. We had two failures on our 1900's that day as well.

[F900EX]

Yeah.. I am struggling with this one.. My friend was in charge of an RJ that day and he reckons everyone in his company is stumped.. Has to be a logical explanation.

[Another Number]

I guess they've looked into whether it had anything to do with implementing a Bransonesque singalong on takeoff.... trouble was, the Annual Denver Soprano Convention is in town, and, well - when the fat lady sings... :ooh::p

[boredcounter]

Lost count of the number of CRJ windscreens that ruined my day working them in Ops for 5 or 6 years. Almost a 'known defect' :ugh:
Even had one go on turnaround, inbound fully serviceable, outbound cancelled, screen just went when nobody was looking.
I put my money with Triplex.............

[F900EX]

Yeah.. However in this instance it was not just RJ's.. The Frontier fleet was also affected.. A319's....

Weird if you ask me.

[ICT_SLB]

CRJ windshield heat also goes into LOW automatically when on ground. The only time I know of one of our test CRJs having a windshield problem (even after -40 C coldsoaks) was when we ran into hail over Texas - put an end to our HGS testing for the day. Wonder if there was a similar precip event at Denver.

[F900EX]

No precip that day.. .Any other ideas ?

[ICT_SLB]

"No precip that day.. .Any other ideas ?"

Falcon,
If memory serves (and it was several years ago), we were descending into the airport when we got hit but there was no report of hail at the surface - think really mean virga. Cracked the outer on the co-pilot's main windshield but no other damage to structure not even a dent.

[vapilot2004]

NTSB calling in glass specialist:

DENVER -- Why windshields cracked on at least 14 airplanes at Denver International Airport during a storm last week remains a mystery, prompting the National Transportation Safety Board to call in a glass specialist.

"We are not discounting anything," Federal Aviation Administration spokesman Allen Kenitzer, whose agency is among those investigating the incident, said Tuesday. "We believe it is very remarkable to have this number of events in the same area at the same time."

The National Transportation Safety Board said its glass specialist will examine 22 damaged front and side windshields that were removed from affected airplanes, investigator Jennifer Kaiser said.


Wind gusts of up to 50 miles per hour were recorded at the airport and there were rapid temperature changes and some snow Friday afternoon when airlines reported the cracked windshields.

Kaiser said the NTSB is also investigating whether an air pressure change may have contributed, she said.

DIA spokesman Chuck Cannon said airport operations and maintenance employees could offer no explanation for the windshield problems. "It's baffling," he said.

SkyWest Airlines, a regional carrier for United Airlines, reported nine planes suffered windshield cracks, while Frontier Airlines said four of its aircraft suffered similar damage. One plane from Great Lakes Airlines suffered a cracked windshield, Kaiser said.

NTSB's Kaiser confirmed that there were no reports of impact from flying debris.

[RatherBeFlying]

winds of up to 100 mphmay be a clue as high wind velocities usually come with a rapid change in temperature and pressure.

Air transport windshields do tolerate temperature extremes and pressure differentials, but a sudden temperature and/or pressure change may be too much.

[bomarc]

FOD BLAMED FOR CRACKED WINDSHIELDS AT DIA
(http://www.avweb.com/eletter/archives/avflash/817-full.html#194571)
Although windborne debris was at first dismissed as a cause for the 14
cracked aircraft windshields last week at Denver International Airport
(http://www.avweb.com/avwebflash/news/Cracked_Windshield_Mystery_194513-1.htmltarget=_blank),
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 (http://origin.denverpost.com/news/ci_5318769). 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.
http://www.avweb.com/eletter/archives/avflash/817-full.html#194571

[themoonsaballoon]

Have seen a spate of failed windscreens on Global Expresses at Jeddah caused by FOD damage from Jet Blast and debris borne by it.
TMAB

[F900EX]

If blowing grit was actually the culprit is it not reasonable to assume that there could be some engine damage that is not immediately obvious. I certainly wouldnt like to think that I ingested sand.

I imagine the damage could manifest itself a little later during a critical moment.

[OVERTALK]

Does anybody really believe that a wind gusting to a maximum of 48 MPH could pit a windscreen sufficiently to make them crack - courtesy of some fine grit?
.
And do it on all four windscreens of the one parked jet (by artfully and deviously turning around corners)?
.
I've flown low-level through heavy desert sandstorms and arctic blizzards at 400+kts with nary a scratch on a heated windscreen.
.
For the pressure concept, think "square of the indicated airspeed" folks.
.
This is all about heating from cold-soak and how you go about it.

[BackPacker]

The only alternative explanation that I can think of, having read the others, is an unusually steep inversion. Any chance we can dig up a vertical temperature profile from somewhere?

Still doesn't explain the windsheets that cracked on the ground though.