# NTSB ANC98LA014: Douglas DC-6B, N861TA, Mcgrath, AK, January 2, 1998 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: January 2, 1998, 15:26 local (19:26 UTC) - Place: Mcgrath, AK - Coordinates: 63.610347, -154.779434 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=63.6103&lon=-154.7794&mi=10 - Phase of flight: [Takeoff](https://openairdocs.org/ntsb-phases/300) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed, report February 15, 2001 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - NTSB case key (mKey): 3109 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC98LA014 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/3109/pdf - Page: https://openairdocs.org/ntsb/ANC98LA014 ## Probable cause The ingestion of snow into the windshield anti-ice system, and the resulting obscured windshield which made runway alignment not possible. Factors associated with this accident were the cold windshield, the reduced performance of the windshield anti-ice because of the short taxi by the crew, and the insufficient information on the system provided by the manufacturer. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, takeoff - roll/run - anti-ice/deice system,windshield - ice ingestion (cause) - anti-ice/deice system,windshield - too cold (contributing factor) - anti-ice/deice system - diminished, pilot in command (contributing factor) - information insufficient, kit manufacturer (contributing factor) - On ground/water encounter with terrain/water, takeoff - aborted - window,flight compartment window/windshield - obstructed - proper alignment - not possible, pilot in command (cause) - terrain condition - berm - Fire, takeoff - aborted ## Analysis During the takeoff roll, while passing 45 knots indicated airspeed, ice formed between the inner and outer panes of the airplane's windshield, obscuring the crew's vision. The flight crew aborted the takeoff, the airplane drifted off the left side of the snow covered runway, and caught fire. The crew reported the airplane and windshield were cold soaked and the temperature was -10 degrees Fahrenheit. The windshield anti-ice system blows air from a combustion heater between the windshield glass panes. The air source for the heater, once the airplane has forward airspeed, is two leading edge wing scoops. The crew told the NTSB investigator that the taxi time was too short for the windshield to warm up, and that during the taxi, snow was circulated around the airplane and into the wing scoops. ## Factual narrative On January 2, 1998, at 1526 Alaska standard time, a Douglas DC-6B airplane, N861TA, departed the edge of runway 34 during an aborted takeoff from the Nixon Fork Mine landing strip, thirty miles north of McGrath, Alaska. The transport category airplane was destroyed by a postcrash fire. The airline transport certificated pilot, and the other two flight crewmembers, were uninjured. The airplane was operated by Woods Air Fuel, Inc., of Palmer, Alaska. The flight was operated under 14 CFR Part 125 as a cargo flight transporting ore concentrate from Nixon Fork Mine. The flight originated from Palmer at 1230, and was on the takeoff roll of the return leg. Visual meteorological condition prevailed at the time of the accident, and an IFR flight plan was on file. The captain reported that at an indicated airspeed of 45 knots during the takeoff roll, ice formed between the inner and outer windshield panes, with the icing following the flow of heated air through the windshield. The crew's forward visibility was obscured, and the takeoff was aborted. The captain reported that the airplane drifted left into snow berms on the side of the 4,200 feet long by 85 feet wide runway and caught fire. The three crewmen evacuated the airplane without injury. The three crewmen relayed to the NTSB investigator that after arrival at the mine strip, the airplane and windshield cold soaked for about one hour in the -10 degree Fahrenheit temperature. After loading the airplane, they taxied for only a few minutes in light, powdery snow, before beginning the takeoff roll. The crewmen stated that the windshield anti-ice system was activated, but because of the short taxi, did not have time to warm completely. All crewmembers indicated that during the taxi, snow was circulated around the airplane and the wing scoops. Research revealed that the windshield anti-ice system was modified as part of installing Supplemental Type Certificate (STC) number 981SO on June 26, 1987. This STC eliminated the superchargers on engines numbers 3 and 4 from providing conditioned air to the airplane's cabin. The modification was part of a conversion to a cargo configuration. The modified cockpit heating and windshield anti-ice system receives supply air from one of two sources. On the ground, a blower fan draws air from the underside of the fuselage for a combustion heater. As the airplane transitions to flight, ram air pressure from two wing leading edge scoops becomes greater than ground blower discharge air, and becomes the heater air supply source. Air and any particulate matter in the wing scoops and ducting passes directly to the heater. Once airborne, the blower fan is deactivated by a weight on wheels switch. From the heater the warm air is ducted directly to the windshield, where it flows between the outer glass pane and the inner vinyl pane, and is then discharged into the cockpit. The "DC-6 Airplane Operating Manual" used by two other companies states "...Certain combinations of temperature and humidity will cause moisture to condense from the air between the windshield panels and settle on the inner surfaces of the glass, obscuring vision. Once formed, anti-icing airflow with heater operation will be required to clear the panels." This language is not included in the STC literature, nor in the flight handbook for the company operating the accident airplane. ## Aircraft - Registration: [N861TA](https://openairdocs.org/deregistered/N861TA-1998-04-20), registration cancelled 1998-04-20, S/N 43522 (OpenAirDocs) - Reported make and model: Douglas DC-6B - Registry model: [Douglas DC-6B](https://openairdocs.org/model/douglas-dc-6b) (registry code 3021712) (OpenAirDocs) - Category: Airplane - Serial number: 43522 - Airframe hours: 46626 - Engines: P&W R-2800-CB-16 2400 horsepower reciprocating - Damage: Destroyed - Fire: On-Ground - Flight: Part 125 - Registered owner: Woods Air Fuel, Inc. - Airworthiness certificate: Standard, Transport - Last inspection: AAIP, December 22, 1997, 25 hours before - Departed: NFR, NIXON FORK MINE, AK - Destination: PAQ, PALMER, AK - Flight plan: IFR - Airport: NFR, Nixon Fork Mine Strip, runway 34, 4,200 × 85 ft, snow ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 55; airline transport, flight instructor, flight engineer, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, valid medical--w/ waivers/lim; seat: left; flight hours: 27,000 total, 16,000 in this make and model, 24,000 as pilot in command, 250 in the last 90 days, 55 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: calm - Visibility: 60 statute miles - Lowest ceiling: none - Temperature: -9 °F ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19980102000029A](https://openairdocs.org/incident/19980102000029A), Jan 2, 1998: Doug STCDC6, Mcgrath, AK, Destroyed. Windshield fogged on takeoff roll. Aborted. Veered into snow bank edge of runway. Caught fire. Evacuated safely. (From .4) during the takeoff roll, while… ## Other investigations on N861TA (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB ANC96LA042](https://openairdocs.org/ntsb/ANC96LA042), Apr 1, 1996: Douglas DC-6-B (N861TA), Beluga, AK, substantial damage. Probable cause: The Pilot-in-Command's selection of an unsuitable terrain area for taxi/parking and his misjudgment of the clearance required. From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.