# NTSB FTW98FA364: Beech 1900D, N251GL, Denver, CO, August 19, 1998 - Type: NTSB accident investigation - Classification: Accident · Minor injuries · Field investigation · Final report - Date: August 19, 1998, 17:15 local (23:15 UTC) - Place: Denver, CO - Coordinates: 39.85009, -104.700897 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.8501&lon=-104.7009&mi=10 - Phase of flight: [Initial climb](https://openairdocs.org/ntsb-phases/350) (OpenAirDocs' grouping) - Highest injury: Minor injuries - Injuries: 1 minor, 14 uninjured - Status: Completed, report February 11, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 43758 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW98FA364 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/43758/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=43758 - Page: https://openairdocs.org/ntsb/FTW98FA364 ## Probable cause Debonding of the propeller erosion shield due to an improper overhaul and repair by other maintenance personnel. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, takeoff - initial climb - propeller system/accessories,leading edge cap - debonded (cause) - maintenance,major repair - improper, other maintenance personnel (cause) - fuselage,cabin - penetrated - precautionary landing - performed, pilot in command ## Analysis Shortly after the airplane took off, the crew heard a loud noise and felt a slight vibration from the left propeller. They returned and landed. It was discovered that the propeller erosion shield had debonded and a portion had penetrated the passenger cabin just aft of the airstair door, knocked ajar Seat 1A Passenger Service Unit, ricocheted off the ceiling, and penetrated the inner window pane at Seat 2C. Laboratory examination of the propeller blade revealed an area 'consistent with adhesive disbonding (debond) on about 80% of the total bond area...' Three hundred hours before the accident, the blade had been overhauled and repaired. The repaired area contained numerous voids, air bubbles, dirt and debris. Evidence of chaffing (rubbing) was found at several locations in the debonded area, indicative of movement between the debonded erosion shield and the propeller blade body. Samples of the erosion shield adhesive were tested and found to have been mixed in improper proportions, reducing bond strength. ## Factual narrative HISTORY OF FLIGHT On August 19, 1998, at 1715 mountain daylight time, a Beech 1900D, N251ZV, owned by Mesa Airlines, Inc., of Farmington, New Mexico, and operated by Great Lakes Aviation, Ltd., of Spencer, Iowa, as United Express flight 1605, was substantially damaged when the erosion shield separated from one of the left propeller blades and punctured the pressure vessel during initial climb at Denver, Colorado. There were no injuries to the airline transport-rated captain, commercial certificated first officer, and 12 passengers, but one passenger sustained a minor injury. Visual meteorological conditions prevailed, and an IFR flight plan had been filed for the scheduled domestic passenger flight operating under Title 14 CFR Part 135. The airplane taxied from its gate at 1710, and took off from runway 17R at 1714. The following was contained in the captain's discrepancy report: "Reaching 500 feet agl [above ground level] after takeoff, heard loud 'bang.' Slight vibration from left prop. Returned for landing. Discovered hole in fuselage from prop leading edge strip." The airplane returned to Denver and landed on runway 17L at 1719 and arrived at its gate at 1725. Postaccident examination revealed the entire erosion shield was missing. There were three holes punctured in the fuselage. The first hole was about 12 inches aft of the airstair door and just above the cabin window. The second hole was slightly higher than the first. The third hole was at the top of the fuselage. A portion of the erosion shield entered the cabin and knocked out the overhead passenger service unit at seat 1A. Two small dents were found in the ceiling. The inner window pane at seat 2C was punctured and a piece of the erosion shield was found lodged between the inner and outer panes. Another piece was found between the ceiling and the pressure vessel. The passenger seated in row 2C sustained a small cut on his forehead when he was grazed by a piece of the shrapnel. He refused medical treatment. AIRCRAFT INFORMATION N251ZV (s.n. UE-251), a Beech 1900D, was manufactured by the Raytheon Aircraft Corporation in 1996. It was equipped with two Pratt and Whitney PT6A-67D engines, driving two Hartzell HC-E4A-31 composite propellers. The propeller blades are made of Kevlar, fiberglass, foam and epoxy. A metallic erosion shield is bonded to the leading edge of the propeller blades, and de-icing boots are bonded to the inboard end of the erosion shield and propeller blade body. According to the aircraft maintenance records, the four propeller blades were last overhauled and repaired by Aircraft Propeller Service, Inc., in July 1998. TESTS AND RESEARCH The four composite blades from the left propeller were removed from the airplane and sent to NTSB's Materials Laboratory in Washington, D.C., where, on August 27, 1998, they were examined. According to the Materials Laboratory's Factual Report (No. 99-23, attached), the surface of the damaged blade (s.n. 811) was smooth and shiny, "consistent with adhesive disbonding (debond) on about 80% of the total bond area...The remaining outboard separation area had a much rougher powdery white appearance typical on cohesive separation within the bonding material." The report further stated that the propeller blade (s.n. 811) had been repaired by injecting adhesive into the joint. This repair reportedly occurred approximately 300 hours before. The repaired area was readily apparent during the examination because it contained numerous voids, air bubbles, dirt and debris. Evidence of chaffing (rubbing) was found at several locations in the debonded area, indicative of movement between the debonded erosion shield and the propeller blade body. The other three blades (1802, 808, and 806) appeared to be undamaged when visually inspected, but tap tests indicated approximately 80 to 90% debonding of the erosion shield under the deice boots on blades 1802 and 808. Blade 806 had "spotty" debonding. When the deice boots were removed, the erosion shields on blades 808 and 806 were found to be cracked. Samples of the erosion shield adhesive were removed and forwarded to the manufacturer for analysis. Using differential scanning calorimetery (DSC), the samples were found to be "fully cured," and contained no "environmental contaminants" such as water or solvents. Further tests of the adhesive, Hysol EA 9330, showed that the cured mixture contained approximately 120 to 140% (by weight) of the recommended amount of part B of the epoxy. A mixing ratio of 100:33 of part A (hardening components) to part B (catalyzers) is recommended by the data sheet. In a report prepared for Hartzell Propellers by the University of Dayton Research Institute, it was found that decreased bond strength would result if Hysol EA 9330 was improperly mixed (such as a 20 to 40% excess of part B). Oil and dirt contamination detected on the blade surfaces would also reduce bonding strength of the joint. However, it could not be determined if the contamination was introduced before or after the erosion shield debonded. Finally, the report noted that exposure to high temperatures could cause a separation. ADDITIONAL INFORMATION The airplane was released to Great Lakes Aviation for repairs on August 20, 1998. After being examined at NTSB's laboratory, the composite blades from the left propeller were sent to Hartzell Propellers. Hartzell Propellers then sent four new replacement propeller blades to Great Lakes Aviation on September 1, 1998. In addition to the Federal Aviation Administration, parties to the investigation included the Raytheon Aircraft Corporation, Great Lakes Aviation, Hartzell Propellers, and Aircraft Propeller Service, Inc. ## Aircraft - Registration: N251GL (not matched to a registry record) - Reported make and model: Beech 1900D - Category: Airplane - Serial number: UE-251 - Airframe hours: 4142 - Engines: P&W PT6A-67D 1279 horsepower turbo prop - Damage: Substantial damage - Flight: Part 121 - Operator: Great Lakes Aviation, Ltd., doing business as United Express - Registered owner: Mesa Airlines, Inc. - Airworthiness certificate: Standard, Transport - Last inspection: Continuous airworthiness, August 15, 1998, 34 hours before - Departed: DEN - Destination: RKS, ROCK SPRINGS, WY - Flight plan: IFR - Airport: DEN, Denver International, runway 17R, 12,000 × 150 ft, concrete ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 27; airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 1,700 total, 700 in this make and model, 840 as pilot in command, 200 in the last 90 days, 40 in the last 30 days, 8 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 140° at 9 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 81 °F, dew point 46 °F - Altimeter: 30.00 inHg - Observed at: DEN ## Docket (26 files) The files NTSB released with the investigation on June 17, 1999, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=43758. 7.4 MB in all. - Supplement C - Wreckage Documentation (item 1, .PDF, 465 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106255&FileExtension=.PDF&FileName=Supplement%20C%20-%20Wreckage%20Documentation-Master.PDF - Supplement D - Cockpit Documentation (item 2, .PDF, 406 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106256&FileExtension=.PDF&FileName=Supplement%20D%20-%20Cockpit%20Documentation-Master.PDF - Supplement E - Second Pilot Information (item 3, .PDF, 132 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40466703&FileExtension=.PDF&FileName=Supplement%20E%20-%20Second%20Pilot%20Information-Redacted.PDF - Supplement S - Aircraft Occupant and Injured Ground Personnel (item 4, .PDF, 71 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106258&FileExtension=.PDF&FileName=Supplement%20S%20-%20Aircraft%20Occupant%20and%20Injured%20Ground%20Personnel-Master.PDF - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 5, .PDF, 376 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40466704&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Materials Laboratory Factual Report (item 6, .PDF, 685 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40466705&FileExtension=.PDF&FileName=Materials%20Laboratory%20Factual%20Report-Redacted.PDF - Propeller Erosion Strip Failure Analysis (item 7, .PDF, 2.6 MB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106260&FileExtension=.PDF&FileName=Propeller%20Erosion%20Strip%20Failure%20Analysis-Master.PDF - FAA ATC Report (item 8, .PDF, 938 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40466706&FileExtension=.PDF&FileName=FAA%20ATC%20Report-Redacted.PDF - Aircraft Propeller Service, Inc. Teardown/Work Order (item 9, .PDF, 196 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40466707&FileExtension=.PDF&FileName=Aircraft%20Propeller%20Service,%20Inc.%20Teardown%2FWork%20Order-Redacted.PDF - FAA Form 8130-3 Airworthiness Approval (item 10, .PDF, 123 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40466708&FileExtension=.PDF&FileName=FAA%20Form%208130-3%20Airworthiness%20Approval-Redacted.PDF - Airplane Diagram Depicting Damage (item 11, .PDF, 92 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106264&FileExtension=.PDF&FileName=Airplane%20Diagram%20Depicting%20Damage-Master.PDF - Passenger Manifest and Seating Assignments (item 12, .PDF, 47 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106265&FileExtension=.PDF&FileName=Passenger%20Manifest%20and%20Seating%20Assignments-Master.PDF - Airplane Floor Plan Depicting Trajectory of Shrapnel (item 13, .PDF, 89 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106266&FileExtension=.PDF&FileName=Airplane%20Floor%20Plan%20Depicting%20Trajectory%20of%20Shrapnel-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 14, .PDF, 102 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40466709&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 15, .PDF, 86 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40466710&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Redacted.PDF - Photo #1: Shrapnel penetration of cabin just aft of airstair door. (item 16, .PDF, 105 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106269&FileExtension=.PDF&FileName=Photo%20%231%3A%20Shrapnel%20penetration%20of%20cabin%20just%20aft%20of%20airstair%20door.-Master.PDF - Photo #2: Close up view of damage to forward cabin area. (item 17, .PDF, 94 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106270&FileExtension=.PDF&FileName=Photo%20%232%3A%20Close%20up%20view%20of%20damage%20to%20forward%20cabin%20area.-Master.PDF - Photo #3: Vertical and horizontal stabilizer damage. (item 18, .PDF, 138 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106271&FileExtension=.PDF&FileName=Photo%20%233%3A%20Vertical%20and%20horizontal%20stabilizer%20damage.-Master.PDF - Photo #4: Seat 1A Passenger Service Unit (PSU) knocked ajar by penetrating shrapnel. PSU also contained ceiling floodlight lens that was shattered. (item 19, .PDF, 91 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106272&FileExtension=.PDF&FileName=Photo%20%234%3A%20Seat%201A%20Passenger%20Service%20Unit%20(PSU)%20knocked%20ajar%20by%20penetrating%20shrapnel.%20PSU%20also%20contained%20ceiling%20floodlight%20lens%20that%20was%20shattered.-Master.PDF - Photo #5: Overhead cabin ceiling depicting indentations made by shrapnel after passing through Seat 1A Passenger Service Unit. (item 20, .PDF, 93 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106273&FileExtension=.PDF&FileName=Photo%20%235%3A%20Overhead%20cabin%20ceiling%20depicting%20indentations%20made%20by%20shrapnel%20after%20passing%20through%20Seat%201A%20Passenger%20Service%20Unit.-Master.PDF - Photo #6: Inner pane of Seat 2C window. After penetrating cabin at Seat 1A Passenger Service Unit and ricocheting off of cabin ceiling, shrapnel penetrated inner window pane at seat 2C and became lodged between inner and oute (item 21, .PDF, 54 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106274&FileExtension=.PDF&FileName=Photo%20%236%3A%20Inner%20pane%20of%20Seat%202C%20window.%20After%20penetrating%20cabin%20at%20Seat%201A%20Passenger%20Service%20Unit%20and%20ricocheting%20off%20of%20cabin%20ceiling,%20shrapnel%20penetrated%20inner%20window%20pane%20at%20seat%202C%20and%20became%20lodged%20between%20inner%20and%20oute-Master.PDF - Photo #7: Front view of damaged propeller blade. (item 22, .PDF, 90 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106275&FileExtension=.PDF&FileName=Photo%20%237%3A%20Front%20view%20of%20damaged%20propeller%20blade.-Master.PDF - Photo #8: Cambered surface of damaged propeller blade. (item 23, .PDF, 92 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106276&FileExtension=.PDF&FileName=Photo%20%238%3A%20Cambered%20surface%20of%20damaged%20propeller%20blade.-Master.PDF - Photo #9: Back surface of damaged propeller blade. (item 24, .PDF, 92 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106277&FileExtension=.PDF&FileName=Photo%20%239%3A%20Back%20surface%20of%20damaged%20propeller%20blade.-Master.PDF - Photo #10: Close up view of damaged propeller balde. (item 25, .PDF, 91 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106278&FileExtension=.PDF&FileName=Photo%20%2310%3A%20Close%20up%20view%20of%20damaged%20propeller%20balde.-Master.PDF - Photo #11: Close up view of damaged propeller blade tip. (item 26, .PDF, 77 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40106279&FileExtension=.PDF&FileName=Photo%20%2311%3A%20Close%20up%20view%20of%20damaged%20propeller%20blade%20tip.-Master.PDF From the NTSB's public API. 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