GRAND CANYON PK, AZ, USA
N32GA
Aerospatiale AS350B
While descending on an aerial tour flight with six passengers, the left side bubble window separated from the helicopter and impacted a tail rotor blade. The pilot made a precautionary landing in the canyon without further incident. Neither the separated window nor its doorframe attachment seal (gasket) was recovered. Examination of the helicopter's tail rotor blade found it bent and scratched with areas of debonded material. The damaged blade was not repairable. During preflight inspection the pilot did not see any damage to the window, and during the flight the left seated passenger was not observed pressing on it. Due to observed cracks in the previous window 4.5 months and 589 flight hours earlier, it had been replaced with a window removed from another helicopter. No maintenance record entry was found for the window installation. The operator's replacement window was manufactured under a FAA Supplemental Type Certificate. The STC holder said that if its 'wedge' window is not properly installed, or if it becomes cracked or damaged due to exposure to harmful cleaning solvents, its integrity may be compromised. The operator reported that if a small crack existed near the window's edge, it may not have been noticed/reported by the pilot due to a lack of conspicuity. The reason(s) for the window separation could not be determined.
HISTORY OF FLIGHT On February 1, 1999, about 1010 hours mountain standard time, an Aerospatiale AS350B, N32GA, operated by Silverado Helicopters, Inc., d.b.a. Heli USA, experienced the sudden loss of the entire left side passenger bubble window during descent over the Grand Canyon National Park, Arizona. The window impacted and damaged a tail rotor blade (paddle). Visual meteorological conditions prevailed during the on-demand sightseeing flight that was performed under 14 CFR Part 135. The commercial pilot landed without further mishap near the south side of the Colorado River in Arizona, about 2 miles from the Grand Canyon West Airport. The airplane sustained minor damage; neither the commercial pilot nor the six passengers were injured. The aerial tour flight originated from Las Vegas, Nevada, at 0928. The pilot reported to the National Transportation Safety Board investigator that during his preflight inspection he had looked at the window and it did not appear damaged. Specifically, no abrasions, lacerations, cracks, or stop-drilled holes were observed. During the flight the passenger seated next to the window was not observed taking pictures or "elbowing" the window. AIRCRAFT INFORMATION The operator reported that the previous left side bubble window had been observed cracked during a 5,000-hour inspection of the helicopter. The cracked window was removed, and it was replaced with a window that had been removed from another of the operator's helicopters, N122AS, which had a total airframe time of about 5,527 hours. This work was completed on August 21, 1998. No maintenance record entry was made for the replacement window's installation in N32GA, which had about 9,154.0 hours recorded on its airframe. The operator reported it believes the replacement window that separated from the helicopter was not manufactured by Aerospatiale. The operator indicated to the Safety Board investigator that the window was obtained from Aeronautical Accessories, Inc., which holds a Supplemental Type Certificate for the "Wedge Window, 7 place" part number 350-903-001. WRECKAGE AND IMPACT INFORMATION The operator sent the damaged tail rotor blade to American Eurocopter for evaluation and possible repair. Following a damage assessment review by Eurocopter France, the Quality Assurance Department of American Eurocopter's USA facility reported to the Safety Board investigator that the blade was found with a debonded area located about 295 mm inboard from the tip of the blade's upper surface. In the debonded area, a 0.43 mm deep score mark was also observed in the skin of the blade. In addition, the straightness of the blade was measured, and it was found out of tolerance. Eurocopter reported that the blade was not repairable, and it should be scrapped. TESTS AND RESEARCH According to written and verbal information provided to the Safety Board investigator by management at Aeronautical Accessories, Inc., it manufactures a wedge window under STC Number SR00183AT, which the operator may have utilized in its helicopter. The manufacturer provides specific instructions for the installation of its windows. In pertinent part, the manufacturer indicates that the window is properly installed in the helicopter's doorframe from the inside of the door using a rubber seal (gasket) to hold it in place. It should not be installed from the outside. Application of excessive pressure on the window assembly or pulling the string too fast may cause damage to the rubber seal assembly. The manufacturer also reported that if the printed installation instructions are not followed, it is possible to install the window backwards. If installed backwards, the window can be displaced upon application of pressure. A window that has been properly installed, and is undamaged, will last indefinitely if maintained without using harmful solvents. The manufacturer additionally indicated that the window's design has not been changed since it was originally certified in November 1991. The window's overall size is larger than the opening in the door. If pressure is applied to the window, it would likely break prior to displacing the amount of material in the overlap area. The manufacturer indicated it has not received information regarding any previous in-flight separations. The helicopter operator's assistant director of operations verbally indicated to the Safety Board investigator that in the Nevada heat, cracks might develop in windows. A small crack located near the window's edge may not have been noticed/reported by the pilot due to a lack of conspicuity, or for other reasons. ADDITIONAL INFORMATION The operator did not report the circumstances of the mishap to the Federal Aviation Administration or to the Safety Board until several days after the helicopter had been returned to service and a replacement tail rotor blade installed. The window and its associated retention gasket (seal) remain missing. The passengers who had been onboard during the incident flight were not interviewed by the Safety Board investigator because the operator did not identify them. The Safety Board investigator requested that the pilot provide a written statement regarding the conditions and circumstances of the mishap flight. An additional request was made to the operator for completion of the accident report form. The pilot's statement and a partially completed accident report form was received on November 22, 1999.
The in-flight separation of a side window for undetermined reasons.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
