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On February 16, 2007, at 1235 mountain standard time, an Airbus Industries A319-111, N927FR, operated as Frontier Airlines Flight 659, experienced a right main windshield fracture during the initial climb out. The airplane performed an uneventful air turn back and landed without further incident. Visual meteorological conditions prevailed at the time of the incident. The scheduled domestic passenger flight was being operated under the provisions of Title 14 Code of Federal Regulations, Part 121. An instrument flight rules flight plan had been filed and no one was injured. The flight originated at Denver International Airport (DEN), Denver, Colorado, and was en route to San Francisco International Airport (SFO), San Francisco, California.
According to the captain, they had just taken off from runway 34L and were making a turn to a heading of 270 degrees when they noticed the first officer's windshield cracking and beginning to arc. The captain alerted Air Traffic Control that they were returning to the airport, and he noticed that his windshield was also cracking, but not arcing. The first officer's windshield stopped arcing and the flight crew landed the airplane without further incident.
During the course of the afternoon, 14 airplanes experienced 26 fractured windshields. One flight crew reported that during the landing roll they "heard a loud thump" and observed the first officer's windshield "spider web." They did not observe anything impacting the windshield. Another flight crew reported taxiing through "dirt and dust being blown around." Their windshield fractured after the airplane was parked at the gate.
The closest official weather observation station was DEN. The elevation of the weather observation station was 5,431 feet mean sea level (msl). The routine aviation weather report (METAR) for DEN, issued at 1239, reported, winds, 010 degrees at 28 knots, gusting to 36 knots; visibility, 10 statute miles; sky condition, few 4,000 feet, scattered 6,000 feet, broken, 10,000 feet; temperature 03 degrees Celsius (C); dewpoint, minus 03 degrees C; altimeter, 29.88 inches. The remarks section stated a peak wind was recorded at 1236 as 350 degrees at 36 knots, wind shift recorded at 1219.
The METAR issued at 1553, reported winds, 350 degrees at 33 knots, gusting to 44 knots; visibility 10 statute smiles; sky condition, scattered 1,200 feet, broken 6,500 feet, overcast 10,000 feet; temperature, 0 degrees C; dewpoint, minus 03 degrees C; altimeter, 29.98. The remarks section stated a peak wind was recorded at 1527 as 010 degrees at 46 knots.
Denver International Airport is located at a field elevation of 5,342 feet msl, 16 miles northeast of Denver, Colorado. The airport has six runways, including two sets of parallel north/south runways (16/34, 17/35) and two east/west runways (07/25, 08/26). Three airport terminals are centrally located, positioning the airplanes in a north/south direction for parking.
The airport is surrounded on all boundaries by open fields. A landfill is located to the west of the airport. Active construction was taking place to the southwest of the airport at the time of the event. Prior to the event, several snowstorms had impacted the Denver area, leaving several feet of snow on the ground. The airport mitigates ice and snow on the runways and taxiways with the use of runway sand. According to their standard, this sand shall consist of "washed granular mineral sand particles, free of stones, clay, debris, slag, and chloride salts, and other corrosive substances." Sand and dirt was observed on the runways, taxiways, and ramp areas following the event.
TESTS AND RESEARCH
On March 5, 2007, the windshields were examined by NTSB investigators and representatives from PPG Industries, Inc., Saint Gobain Sully, and the Federal Aviation Administration. Two of the windshields examined were sent to the PPG, Inc., facility in Huntsville, Alabama, for additional detailed examination. Two additional windshields that were determined to be part of the event, but not examined on March 5, were also sent to PPG for examination. These four windshields were examined under the auspices of the National Transportation Safety Board on April 15, 2007.
One Beech 1900D airplane (N245GL), owned and operated by Great Lakes Aviation LTD, suffered a fractured right forward windshield. Examination of the windshield revealed multiple impact markings on the outer ply, across the entire outer surface. One Airbus A318-111 airplane (N807FR), operated by Frontier Airlines, suffered a fractured left windshield. Examination of the windshield revealed few impact markings on the outer ply, across the entire outer surface.
Two Embraer EMB-120ER airplanes (N299SW and N271YV), operated by Skywest Airlines, suffered fractures of the left and right forward windshields and the left forward windshield, respectively. Examination of the left windshield on N271YV revealed one impact mark on the outer surface of the outer ply. No other impact marks were identified. Examination of the right windshield on N299SW revealed few impact markings on the outer ply, concentrated in the lower forward quarter of the windshield. Examination of the left windshield revealed multiple impact markings on the outer ply, concentrated on the forward half of the windshield.
Two Bombardier CL-600-2B19 airplanes (N410SW and N939SW), operated by Skywest Airlines, suffered fractures of the right forward windshield and the left side windshield respectively. Examination of the side windshield on N939SW revealed few impact markings on the outer ply concentrated on the forward quarter of the windshield. Examination of the windshield on N410SW revealed multiple impact markings on the outer ply, across the entire surface.
Three Airbus A319-111/2 airplanes (N923FR, N927FR, and N909FR), operated by Frontier Airlines, suffered fractures of both the left and right forward windshields. Examination of the windshields on N927FR revealed multiple impact markings on the outer ply, concentrated on the forward third, and numerous significant pits. Examination of both windshields on N923FR revealed multiple impact markings on the outer ply, across the entire surface. Examination of the windshields on N909FR revealed numerous significant pits on the outer ply.
Five Bombardier CL-600-2C10 airplanes (N754SK, N724SK, N753SK, N758SK, and N746SK) operated by Skywest Airlines, suffered fractures of one or more of the left and right forward and left, and right side windshields. Examination of the three windshields from N754SK revealed multiple impact markings on the outer ply of each windshield. Examination of all four windshields on N724SK revealed multiple impact markings on the outer ply of each windshield. Examination of the two windshields on N753SK revealed multiple impact markings on the outer ply, concentrated on the forward quarter and lower forward corner of each windshield. Examination of the one windshield from N758SK revealed multiple impact markings on the outer ply, in the lower forward corner. Finally, examination of the one windshield from N746SK revealed multiple impact markings on the outer ply, concentrated on the lower forward corner of the windshield.