Wednesday, August 22, 2018

Piper PA-31T Cheyenne, N909PW: Accident occurred December 05, 2016 at Missoula International Airport (KMSO), Missoula County , Montana

The National Transportation Safety Board did not travel to the scene of this accident.

Additional Participating Entity: 

Federal Aviation Administration / Flight Standards District Office; Helena, Montana

Aviation Accident Factual Report - National Transportation Safety Board: http://app.ntsb.gov/pdf 


Investigation Docket - National Transportation Safety Board: https://dms.ntsb.gov/pubdms


http://registry.faa.gov/N909PW


Location: Missoula, MT
Accident Number: WPR17LA031
Date & Time: 12/05/2016, 1300 MST
Registration: N909PW
Aircraft: PIPER PA 31T
Aircraft Damage: Substantial
Defining Event: Part(s) separation from AC
Injuries: 2 None
Flight Conducted Under: Part 91: General Aviation - Personal 

On December 5, 2016, about 1300 mountain standard time, a Piper PA-31T airplane, N909PW, made an emergency landing at Missoula International Airport (MSO), Missoula, Montana, following a fracture and separation of the left windshield from the airframe. The private pilot and passenger were not injured. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Instrument meteorological conditions prevailed, and an instrument flight rules flight plan was filed. The flight originated from Kalispell City Airport (S27), Kalispell, Montana at 1215.

The pilot reported that he was in cruise flight at flight level 230 for about 10 minutes, with an outside air temperature of - 40° Fahrenheit, when suddenly the left windshield departed the airplane. At the time of the windshield failure, the pilot heard an abrupt "swish" sound, followed by an instantaneous "loud roar" with a simultaneous blast of freezing air. The pilot and passenger donned their oxygen masks, and the pilot initiated an immediate descent. He made a distress radio call to air traffic control (ATC) declaring an emergency, and stated his intention to divert to Missoula, Montana; however, he was not able to hear a response from ATC due to the noise in the airplane. The pilot landed at MSO without further incident.

The propeller driven, twin engine, low wing, pressurized airplane equipped with a retractable tricycle landing gear system, was manufactured in 1977. It was powered by two Pratt & Whitney Canada PT6 engines, each rated at 620 horsepower. The airplane was equipped with right and left electrically heated main windshields that were manufactured with two layers of glass. Data plates indicated that both windshields were manufactured by PPG Industries in Huntsville, Alabama. The left windshield was manufactured in January 1977 and the right windshield was manufactured in August 1981. A review of maintenance records indicated that the airplane was issued a standard airworthiness certificate on August 26, 1977 and mentioned that the airplane was exported. The next entry in the logbook was dated December 8, 1981, with the total time of 1712.12 hours. The airplane was ferried back to the United States and issued a Standard Airworthiness Certificate on December 17, 1981, with the total time of 1734 hours. There were no logbooks supplied for the period when the airplane was registered overseas. No information was found in the records to indicate when or why the right windshield was replaced. The most recent inspection of the airplane was accomplished on February 1, 2016, at a total time of 6267.5 hours with no discrepancies reported.

The examination of the airplane revealed that most of the left windshield glass and vinyl departed the airframe during the event. The aluminum retainer and the vinyl beneath the fuselage windshield frame remained installed. Small areas of glass and vinyl were present around the edge of the windshield frame. Only a few small glass fragments were found in the cockpit. The right windshield remained intact and installed in the airplane. There was no evidence of impact damage to the fuselage aft of the windshield or the tail of the airplane. There were small fragments of glass embedded in the left propeller blades. No evidence of bird impact was noted anywhere on the airplane. The fuselage windshield frame, sealant, and paint around both windshields were intact. The fractured remains of the left windshield and the intact right windshield were removed and subsequently examined at PPG Aerospace Transparencies, Huntsville, Alabama.

The fractured left windshield aluminum retainer and flange area was intact. Several areas of retainer discoloration with a lighter color (white versus gray) were noted in the flange area on the inboard and outboard sides of the retainer. The largest discolored area was located along the lower flange and extended across the width of the retainer for about 6 inches on both the inboard and outboard sides of the retainer. The area was examined and a white powdery residue consistent with corrosion of the aluminum retainer was present, and the vinyl was no longer adhered to the aluminum.

The right windshield was intact with no fracture of the inboard or outboard glass layers. Areas of retainer discoloration with a lighter color (white versus gray) were noted in the flange area on the inboard and outboard sides of the retainer though it was less severe than the left windshield. These areas were scattered around the periphery of the windshield with varying sizes and there was no large single area like noted on the left windshield. There was cloudiness, interlayer cracking, and delamination noted along the top and bottom edges of the windshield consistent with moisture ingression into the laminate. The discrepancies were noted along the entire upper edge and extended about 3/8 inch from the edge of the outboard glass layer towards the center of the windshield. The same discrepancies were also noted along the forward 13 inches of the lower edge and extended about 1/2 inch from the edge of the outboard glass layer towards the center of the windshield. Delamination was also noted at all four corners and along the bus bars at the lower forward and lower aft ends of the glass area.

The Piper Cheyenne Service Manual provides guidance to operators for window inspection and repair. The manual defines three areas of the windshields: the critical area of the windshield defined as the viewing area used for taxiing, takeoff, climb, cruise and landing; the semi-critical area defined as the viewing area used for general flight vision and the non-critical areas defined as viewing areas normally not used for flight operations. Furthermore, the manual defines anomalies such as distortion, cracks, crazing, scratches, chips, haze, blemishes, mark-off, and delamination for use when inspecting the windshields. Cracks are considered critical for the glass windshields. Cracking of either the inboard or outboard glass layer is cause for immediate replacement. Delamination as evidenced by a cloudy or milky appearance is indicative of moisture or solvent penetration into the windshield laminate. Any delamination present in the critical and semi-critical areas should be replaced at the earliest opportunity. In addition, if the semi-critical section exhibits evidence of chipping of the inner glass surface, the windshield should be replaced.

Pilot Information

Certificate: Private
Age: 43, Male
Airplane Rating(s): Single-engine Land
Seat Occupied: Left
Other Aircraft Rating(s): Glider; Gyroplane
Restraint Used: 3-point
Instrument Rating(s): Airplane
Second Pilot Present: No
Instructor Rating(s): None
Toxicology Performed: No
Medical Certification: Class 3 Without Waivers/Limitations
Last FAA Medical Exam: 04/19/2013
Occupational Pilot: No
Last Flight Review or Equivalent: 04/01/2016
Flight Time:  2235 hours (Total, all aircraft), 132 hours (Total, this make and model), 2104 hours (Pilot In Command, all aircraft), 26 hours (Last 90 days, all aircraft), 0 hours (Last 30 days, all aircraft), 0 hours (Last 24 hours, all aircraft)

Pilot-Rated Passenger Information

Certificate: Private
Age: 39, Female
Airplane Rating(s): Single-engine Land
Seat Occupied: Right
Other Aircraft Rating(s):
Restraint Used: 3-point
Instrument Rating(s):
Second Pilot Present: No
Instructor Rating(s):
Toxicology Performed:
Medical Certification:
Last FAA Medical Exam:
Occupational Pilot: No
Last Flight Review or Equivalent:
Flight Time:  70 hours (Total, all aircraft), 30 hours (Pilot In Command, all aircraft), 0 hours (Last 90 days, all aircraft), 0 hours (Last 30 days, all aircraft), 0 hours (Last 24 hours, all aircraft) 

Aircraft and Owner/Operator Information

Aircraft Make:  PIPER
Registration: N909PW
Model/Series: PA 31T UNDESIGNATED
Aircraft Category: Airplane
Year of Manufacture: 1977
Amateur Built: No
Airworthiness Certificate: Normal
Serial Number: 31T-7720060
Landing Gear Type: Tricycle
Seats:
Date/Type of Last Inspection: 03/01/2016, Annual
Certified Max Gross Wt.:
Time Since Last Inspection:
Engines: 2 Turbo Prop
Airframe Total Time: 6850 Hours
Engine Manufacturer: P&W
ELT: Installed, not activated
Engine Model/Series: PT6A SER
Registered Owner: On file
Rated Power: 620 hp
Operator: On file
Operating Certificate(s) Held: None 

Meteorological Information and Flight Plan

Conditions at Accident Site: Instrument Conditions
Condition of Light: Day
Observation Facility, Elevation: KMSO, 3189 ft msl
Distance from Accident Site:  5 Nautical Miles
Observation Time: 1253 MST
Direction from Accident Site: 305°
Lowest Cloud Condition:
Visibility:  10 Miles
Lowest Ceiling: Broken / 6000 ft agl
Visibility (RVR):
Wind Speed/Gusts: 7 knots /
Turbulence Type Forecast/Actual: / None
Wind Direction: 10°
Turbulence Severity Forecast/Actual: /
Altimeter Setting: 30.02 inches Hg
Temperature/Dew Point: -3°C / -12°C
Precipitation and Obscuration: No Obscuration; No Precipitation
Departure Point: KALISPELL, MT (S27)
Type of Flight Plan Filed: IFR
Destination: LAS VEGAS, NV (LAS)
Type of Clearance: IFR
Departure Time: 1215 MST
Type of Airspace: Class A

Wreckage and Impact Information

Crew Injuries: 1 None
Aircraft Damage: Substantial
Passenger Injuries: 1 None
Aircraft Fire: None
Ground Injuries: N/A
Aircraft Explosion: None
Total Injuries: 2 None
Latitude, Longitude:  46.875833, -113.996944 (est)

NTSB Identification: WPR17LA031
14 CFR Part 91: General Aviation
Accident occurred Monday, December 05, 2016 in Missoula, MT
Aircraft: PIPER PA 31T, registration: N909PW
Injuries: 2 Uninjured.

This is preliminary information, subject to change, and may contain errors. Any errors in this report will be corrected when the final report has been completed. NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

On December 5, 2016, about 1300 mountain standard time, the pilot of a Piper PA-31T, N909PW, made an unscheduled landing at the Missoula International Airport (MSO), Missoula, Montana, after the left windshield fractured and separated from the airplane. The private pilot and passenger were not injured. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Instrument meteorological conditions prevailed and the flight was operated on an instrument rules flight plan. The flight originated from Kalispell City Airport (S27), Kalispell, Montana at 1215.

The pilot reported that he was in cruise flight at 23,000 feet when the left windshield fractured and departed the airplane. He immediately performed an emergency landing to the nearest airport, and landed without further incident. 

The postaccident examination of the windshield revealed that the periphery of the windshield remained attached to the airframe; however, a majority of it separated and has not been located.

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