May 072014
 

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“Atlanta to Los Angeles Delta flight 110 on May 3, 2014: Pressure caused the outer windshield to arch then shatter. Calm pilots landed [Delta flight 110 safely] in [nearby] Albuquerque … ,” according to a recent individual incident report on CNN iReport on May 3, 2014, and CNN Wire on May 6, 2014.

CNN PRODUCER NOTE: Jennifer Squires was on Delta flight 110 flying from Atlanta to Los Angeles on May 3, when halfway through the journey the pilot came over the intercom, and said that the flight needed to make an emergency landing, because the windshield was cracked. The plane descended to an airport in Albuquerque, New Mexico. Once the plane was safely on the tarmac and the passengers were exiting the plane, Squires asked the pilot, if she could see the cracked windshield and was able to take this photo. Overall, she was impressed by the pilot and the crew for navigating them to safety, and she was able to make it to Los Angeles for vacation.

“A spokesperson at the FAA said the outside part of the double-paned windshield shattered, but the interior part remained intact. “Our initial information was that the outside part of the windshield shattered but the interior part remained intact,” wrote FAA spokesman Lynn Lunsford, via email. Also, the aircraft did not depressurize.

“All windows and windshields are at least double-paned,” said Delta spokesman Morgan Durrant said via e-mail. “This is a rare occurrence but the established procedure is to divert the flight.”

What are the Actual Incidences of Cracked or Shattered Cockpit Windshields?

It is the Delta spokesperson’s statement here that gets folks thinking about the actual likelihood or rarity of cracked or shattered cockpit windshield occurrences and such aircraft safety breaches.

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In fact, cracked or shattered cockpit windshield occurrences, during commercial aircraft flights at normal cruise altitudes, ranging 20-38 thousand feet, happen more often than one might think. Every week or two there is a cracked or shattered cockpit windshield incident happening on one of the nearly 90 thousands flights airborne each day (or nearly 33 million flights annually) around the world.

Remarkably, for every cracked or shattered cockpit windshield incident reported, there is likely one that is not reported. International aviation safety protocols among airlines and international transport ministries have varying reporting standards of such incidents. Airlines typically do not like to widely disclose such safety breaches for obvious reasons of natural passenger and crew uneasiness, apprehension, and discomfort.

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During an aircraft safety breach of a cracked or shattered cockpit windshield, as similarly during spasmodic occurrences of aircraft engine malfunctions or failures, the standard procedures in such safety breaches is for the pilots to immediately go on oxygen, and to divert the flight plan. Whereupon communication with air traffic controllers, the pilots immediately lands the aircraft at the nearest airport.

Aircraft Cockpit Windshield Loading and Layered Construction

An aircraft at normal horizontal level cruise, at say 38,000 feet, like that of Delta flight 110, has four primary forces, which are: (i) an upward lift, L, (ii) a downward weight, W, (iii) a forward thrust, T, and (iv) a backward drag, D. The lift-to-drag ratio, L/D, is an aircraft aeronautical design parameter. The aircraft vehicle structural weight opposes the lift, which is also closely-aligned to the vehicle drag, D, (as an inherent function of the lift-to-drag ratio, L/D), and which is also equally-aligned to the thrust, T, (defined as a ratio of the aircraft’s fully-loaded weight, W, to the aircraft’s aeronautical design parameter, L/D).

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An aircraft cockpit windshield principally carries two components of surface loads, a backwardly-directed, horizontal surface drag, d, (opposing some portion of forward vehicle thrust, T), and an upwardly-directed, vertical surface lift, v (opposing some portion of the downward vehicle weight, W).

From a materials engineering standpoint, cockpit windshields, typically weighing between 25-40 pounds, depending on the type of windshield build, are typically constructed of several layers:

(1) A glass face-plate, roughly 1/10″ thick;

(2) A Polyvinyl Butryal (PVB) layer, about 1/8″ thick;

(3) A stretched acrylic layer, approximately 1″ thick;

(4) An additional PVB layer, nearly 1/10″ thick;

(5) An additional stretched acrylic layer, approximately 1″ thick.

During a commercial flight, pilots have to heat the cockpit windshields to address the external environmental elements impacting cockpit windshields. Some aircraft will engage the window heater before descent to “soften” the acrylic layer in case of a strike. Aircraft cockpit windshields are typically designed to withstand the impact of an eight pound bird striking the aircraft front, according to Boeing aircraft engineers. Heating of the windshield makes the windshield more pliable and able to withstand an impact from a ‘bird-strike’.

The nearly 5-6 thousand flight-cycles an airlines’ aircraft asset undergoes produces extreme thermal changes across the cockpit windshields. This can cause moderate flight-cycle fatigue failures of the windshields, inducing face-plate and/or windshield layered construction cracks.

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APPENDIX: Past Incidences of Cracked or Shattered Cockpit Windshields

2013-2014 Cracked Windshield Incidents on a Sample of International Flights: Here is what has been reported so far since last Thanksgiving-Christmas 2013, the highest flight travel season, according to Aviation Herald:

  • US Airways A333 near Charlotte on May 3, 2014, windshield heating issues.
  • Aegean A321 near Munich on May 1, 2014, cracked windshield.
  • Aegean A321 near Brussels on April 19, 2014, cracked windshield.
  • Ethiopian B788 near Rome on April 21, 2014, cracked windshield.
  • United B752 near Indianapolis on April 19, 2014, cracked windshield.
  • Overland AT42 near Lagos on April 7, 2014, cracked windshield
  • Southwest B733 near Boise on April 6, 2014, cracked windshield
  • Gojet CRJ7 near New York on March 22, 2014, shattered windscreen
  • SAS B736 at Oslo on March 13, 2014, cracked windshield
  • Yakutia B737 near Perm on March 3, 2014, cracked windshield
  • Southwest B737 near Pittsburgh on March 1, 2014, cracked windshield
  • UTAir CRJ2 near Brno on January 30, 2014, cracked windshield
  • British Airways B763 over North Sea on February 19, 2014, cracked windshield
  • Niki A320 near Vienna on January 31, 2014, cracked windshield, reported loss of cabin pressure
  • Niki A321 near Faro on February 2, 2014, cracked windshield
  • Srilankan A332 near Colombo on January 1, 2014, cracked windshield
  • Germanwings A319 near Vienna on December 21, 2013, cracked windshield
  • Nordstar B738 at Krasnojarsk on December 17, 2013, cracked windshield
  • Qantas B738 near Newman on November 26, 2013, cracked windshield
  • American B752 near Orlando on November 12, 2013, cracked windshield
  • Tindi DHC7 at Yellowknife on December 14, 2013, “blind” landing (entire windshield, left and right hand, iced over due to no heating available limiting the sight).

2009-2013 Cracked Windshield Incidents on Delta Airlines: Upon doing a quick search for “Delta Cracked,” one obtains the following incidents of cracked cockpit windshields of Delta flights (The other carriers shown are flights operating as Delta Connection):

  • Delta A319 near Memphis on October 2, 2013, cracked windshield.
  • Chautauqua E145 at Richmond on June 28, 2012, rejected takeoff.
  • Pinnacle CRJ9 near Edmonton on January 29, 2012, arcing in cockpit, cracked windshield.
  • Delta B752 near Bahamas on October 10, 2011, cracked windshield.
  • Pinnacle CRJ2 near Indianapolis on June 27, 2011, cracked windshield.
  • Delta B744 over Pacific on June 16, 2011, cracked windshield.
  • Delta B752 near Las Vegas on June 16, 2011, cracked windshield.
  • Skywest CRJ7 at Denver on January 19, 2011, cracked windshield on takeoff.
  • Skywest CRJ2 at Denver on January 19, 2011, cracked windshield on takeoff.
  • Delta B752 at Denver on January 19, 2011, cracked windshield on takeoff.
  • Delta Airlines B738 near Dallas on November 18, 2010, cracked windshield.
  • Atlantic Southeast CRJ7 near Louisville on December 7, 2009, cracked windshield.
  • Delta Airlines B752 near Bogota on December 2, 2009, cracked windshield.
  • Delta Airlines B763 near Quebec on September 23, 2009, cracked windshield.
  • Freedom Airlines E145 near Albany on April 21, 2009, cracked windshield.
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