# NTSB ANC98FA145: de Havilland DHC-2, N1433Z, Port Alsworth, AK, September 9, 1998 - Type: NTSB accident investigation - Classification: Accident · Fatal · Field investigation · Final report - Date: September 9, 1998, 10:45 local (18:45 UTC) - Place: Port Alsworth, AK - Coordinates: 60.200927, -154.280364 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=60.2009&lon=-154.2804&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Fatal - Injuries: 5 fatal - Status: Completed, report March 31, 2000 - Report: Approved by Office Director - NTSB office: Alaska Regional Office - NTSB case key (mKey): 43978 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=ANC98FA145 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/43978/pdf - NTSB docket: https://data.ntsb.gov/Docket?ProjectID=43978 - Page: https://openairdocs.org/ntsb/ANC98FA145 ## Probable cause The pilot's failure to maintain adequate airspeed which resulted in an inadvertent stall. Factors associated with this accident were the pilot's unfamiliarity with the geographic area, the low clouds, his becoming disoriented, and the blind canyon into which he flew. An additional factor was the intentionally disabled stall warning system. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of control - in flight, cruise - stall warning system - disabled (contributing factor) - airspeed - inadequate, pilot in command (cause) - lack of familiarity with geographic area, pilot in command (contributing factor) - weather condition - low ceiling - stall - inadvertent, pilot in command (cause) - spatial disorientation, pilot in command (contributing factor) - In flight collision with terrain/water, descent - uncontrolled - terrain condition - blind/box canyon ## Analysis The float equipped airplane was attempting to cross a mountain pass, following two other company airplanes. The first two pilots, and passengers, described five to seven miles visibility, 700 feet ceilings, clouds hanging on the mountainsides, and misty rain. The route of flight required several turns in the pass. The pilot had not flown through the pass in marginal Visual Flight Rules (VFR) weather before this flight. After the first two airplanes went through the pass, they lost radio contact with the accident pilot, and did not see or hear from him again. The wreckage was later located at the head of an intersecting canyon, two miles before the correct pass. The airplane had been modified with a Short Take Off and Landing (STOL) kit. Canadian certification flight tests had determined that this modification eliminated aerodynamic warning of impending stalls, and therefore required an audible stall warning. Company pilots indicated it was common for the stall warning system to activate at an airspeed 10-15 miles per hour above the actual stall. At the time of the accident, the airplane did not have the ventral fin installed, and a takeoff flaps setting was selected. The audible stall warning circuit breaker was found in the pulled (disabled) position. ## Factual narrative HISTORY OF FLIGHT On September 9, 1998, about 1045 Alaska daylight time, a Dehavilland DHC-2, float equipped airplane, N1433Z, sustained substantial damage when it impacted mountainous terrain about 3,600 feet msl near Telequana Pass, Alaska. The pass is about 48 miles north-northwest of Port Alsworth, Alaska. The commercial pilot and the four passengers sustained fatal injuries. The flight was operated by Rust's Flying Service, Inc., of Anchorage, Alaska. The flight was conducted under 14 CFR Part 135 as an on-demand air taxi transporting hunters from the Lake Hood seaplane base in Anchorage, to a hunting lodge on the Hoholitna River, about 190 miles west of Anchorage. Visual meteorological conditions prevailed at the time of the accident, and a company VFR flight plan was in effect. The accident airplane was the third of three company airplanes crossing the mountain pass, spaced between three and five miles apart. The pilots described the cloud ceilings as 4,500 feet msl at the 3,300 feet msl pass, with five miles visibility. The pilots of the first two airplanes told the NTSB investigator-in-charge (IIC) that they were in radio contact with the pilot of the accident airplane as they crossed through the pass, and then lost radio contact as they descended below the steep terrain. Both lead pilots indicated they believed it was due to terrain, and that when they continued to the west and still were not able to make contact with the airplane, they assumed the pilot had turned around because he saw something he did not like, and was attempting another route. The first two pilots arrived at their destination and noted that the accident airplane had not arrived. They waited about one hour, then continued along their scheduled routes. They told the NTSB IIC that they were concerned when the accident pilot did not arrive, and asked the lodge owner to notify the company if the airplane had not arrived within one hour of their departure. The air taxi company owner told the NTSB IIC that they never received a call from the lodge telling them the airplane had not arrived. At 1235, the Alaskan Air Command Rescue Coordination Center (RCC) began a search after search and rescue satellites received an Emergency Locator Transmitter (ELT) signal on 121.5 MHz. At 1400, the National Park Service dispatched an airplane from Port Alsworth to search for the ELT at the request of RCC. At 1500 the search airplane heard a signal on 121.5 MHz coming from the canyon where the wreckage was discovered. Due to low ceilings and visibility, the airplane pilot requested a helicopter be used to search the canyon. At 1825, the wreckage was located by the crew of an Alaska Air National Guard helicopter. PERSONNEL INFORMATION The pilot held a commercial pilot certificate for single engine land and sea airplanes, and multiengine land airplanes. He held an instrument rating, and a flight instructor rating for single engine airplanes. His most recent second class medical certificate was issued on May 26, 1998, and contained no restrictions. He was an airframe and powerplant mechanic. The pilot was first hired by the company as a mechanic, on March 3, 1998. He had been employed as a pilot since May 1, 1998. This was his first season with this company as a pilot, and his third season flying in Alaska. It was his first season flying in the Alaska Mountain Range area. The Director of Operations and Chief Pilot told the NTSB IIC it was his fourth time through Telequana Pass. They said the previous trips were in better weather conditions than the day of the accident. The pilot was qualified in the Cessna 206 on May 22, 1998, and the DeHavilland DHC-2 on July 17, 1998. The pilot's initial hire flight training and 14 CFR 135.293 competency checks were performed in the Cessna 206. His transition training to the DHC-2 consisted of ground training and a flight examination to meet the requirements for CFR 135.293. Stall maneuvers in the DHC-2 were recorded on the pilot's 135.293 check flight record on July 17, 1998. According to the pilot's personal logbook, and company flight records, at the time of the accident he had accumulated about 1,820 hours of flight time. The pilot had accrued 151 hours of experience in the DeHavilland DHC-2. In the previous 90, and 30 days, he had flown 338 and 118 hours, respectively. Of these, 133 and 59 hours were in the DHC-2. The day prior to the accident he flew five hours, all in the DHC-2. The day of the accident was a scheduled work day for the pilot. The accident flight was the pilot's first flight of the day. AIRCRAFT INFORMATION General The airplane was a Dehavilland DHC-2 Mark I "Beaver," manufactured by the DeHavilland Aircraft Company of Canada. It was registered to Rust Properties, LLC, of Anchorage, Alaska. The airplane was operated by Rust's Flying Service, Inc., of Anchorage. The airplane was powered by a single Pratt & Whitney R-985 radial engine, rated to produce 450 shaft horsepower. The airplane had accumulated 12,948 total hours in operation at the time of the accident. The airplane was configured with seating for the pilot and four passengers. The airplane's maximum allowable takeoff weight was 5,370 pounds. It had STC number SA4025NM incorporated, which provided a gross weight increase from 5,100 pounds. The horizontal stabilizers were modified with Kenmore "finlets" on the stabilizer tips. The airplane did not have a lower surface ventral fin installed underneath the empennage. It was equipped with EDO 4930 nonamphibious floats. The airplane had always been operated on floats while owned by the company. The airplane was modified with an AOG Air Support Baron / STOL (Short Take Off and Landing) kit on May 5, 1994. This modification was approved under U.S. Supplemental Type Certificate (STC) number SA-1070NE, and Canadian Supplemental Type Approval (STA) number SA92-45. This STOL modification consisted of a full span contoured leading wing edge, drooped wing tips, upper wing surface stall fences, and trailing edge flap gap seals. Additionally, an electrically powered, aural stall warning horn was installed as a mandatory component in the modification kit. The airplane was maintained on a 100 hour inspection cycle. The most recent inspection was an annual inspection completed on August 19, 1998, 64 hours prior to the accident. A review of maintenance records revealed no repetitive maintenance problems. Other pilots who had recently flown the airplane did not recall any discrepancies. Weight and Balance The pilot fueled his own airplane. It is unknown how much fuel he placed in the airplane. The pilots of the other two airplanes in the flight said they departed Lake Hood with full fuel in the forward and center tanks, eight gallons in the aft tank, and full tip tanks. They told the NTSB IIC that they expected the accident pilot to use a similar fuel load. 498 pounds of cargo was removed from the airplane (443 pounds at the accident site, and an additional 55 pounds after airplane recovery). An estimated additional 40 pounds of perishable goods was left at the wreckage site. The total cargo accounted for was 538 pounds (443 + 55 + 40 pounds). According to their driver's licenses, the passengers and pilot weighed a combined total of 890 pounds. Using these weights, the estimated weight at the time of the accident was as follows: Empty weight of airplane - 3,386 pounds Pilot and Passengers - 890 pounds Cargo (baggage) -- 538 pounds Zero Fuel Weight - 4,814 pounds Estimated fuel at takeoff - 556 pounds (93 gallons to reach maximum allowable take off weight) Total weight at takeoff - 5,370 pounds Estimated fuel consumption (1 hour 15 minutes) - 150 pounds (25 gallons) Total weight at accident - 5,222 pounds The estimated airplane center of gravity (CG) at the accident site was 104.17 inches aft of datum, with a forward and aft limit of 101.25 and 106.1 inch ## Aircraft - Registration: [N1433Z](https://openairdocs.org/aircraft/N1433Z), registered now, S/N 595 (OpenAirDocs) - Reported make and model: de Havilland DHC-2 - Registry model: [Dehavilland-Kenmore DHC-2](https://openairdocs.org/model/dehavilland-kenmore-dhc-2) (registry code 2805001) (OpenAirDocs) - Category: Airplane - Serial number: 595 - Airframe hours: 12948 - Engines: P&W R-985-AN14B 450 horsepower reciprocating - Damage: Substantial damage - Flight: Part 135 - Operator: Rust'S Flying Service, Inc. - Registered owner: Rust Properties, LLC - Airworthiness certificate: Standard, Normal - Last inspection: 100 hour, August 19, 1998, 65 hours before - Departed: LHD, ANCHORAGE, AK - Destination: HOHOLITNA RIVER, AK - Flight plan: Company VFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 33; commercial, flight instructor, private; airplane ratings: single-engine sea, single-engine land; instrument ratings: airplane; medical: class 2, valid medical--no waivers/lim.; seat: left; toxicology performed; flight hours: 1,720 total, 150 in this make and model, 1,670 as pilot in command, 338 in the last 90 days, 118 in the last 30 days, 5 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 90° at 10 knots - Visibility: 5 statute miles - Lowest ceiling: 4,500 ft overcast ## 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 19980909022849A](https://openairdocs.org/incident/19980909022849A), Sep 9, 1998: Dhav STCDHC2, Anchorage, AK, Substantial damage, 5 fatal. (.4) The float equipped airplane was attempting to cross a mountain pass, following two other company airplanes. The first two pilots, and passengers,… ## Other investigations on N1433Z (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 ANC94LA142](https://openairdocs.org/ntsb/ANC94LA142), Sep 17, 1994: de Havilland DHC2 (N1433Z), Whittier, AK, substantial damage. Probable cause: THE PILOT'S INADEQUATE IN-FLIGHT PLANNING AND INADEQUATE COMPENSATION FOR THE WIND CONDITIONS. AN INITIAL TAIL WIND AND LATER A CROSSWIND WERE FACTORS IN THE ACCIDENT. ## Docket (33 files) The files NTSB released with the investigation on July 19, 1999, on NTSB's docket system: https://data.ntsb.gov/Docket?ProjectID=43978. 6.6 MB in all. - Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1 (item 1, .PDF, 388 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460059&FileExtension=.PDF&FileName=Pilot%2FOperator%20Aircraft%20Accident%20Report,%20NTSB%20Form%206120.1-Redacted.PDF - Supplement A - Wreckage Documentation (item 2, .PDF, 250 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108452&FileExtension=.PDF&FileName=Supplement%20A%20-%20Wreckage%20Documentation-Master.PDF - Supplement B - Cockpit Documentation (item 3, .PDF, 379 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108453&FileExtension=.PDF&FileName=Supplement%20B%20-%20Cockpit%20Documentation-Master.PDF - Supplement K - Occupant, Survival and Injury Information (item 4, .PDF, 403 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108454&FileExtension=.PDF&FileName=Supplement%20K%20-%20Occupant,%20Survival%20and%20Injury%20Information-Master.PDF - Supplement S - Aircraft Occupant and Injured Ground Personnel (item 5, .PDF, 56 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108455&FileExtension=.PDF&FileName=Supplement%20S%20-%20Aircraft%20Occupant%20and%20Injured%20Ground%20Personnel-Master.PDF - Pilot/Witness Statement - Plane #1 (item 6, .PDF, 378 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108457&FileExtension=.PDF&FileName=Pilot%2FWitness%20Statement%20-%20Plane%20%231-Master.PDF - Witness/Pilot Statement - Plane #2 (item 7, .PDF, 212 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460060&FileExtension=.PDF&FileName=Witness%2FPilot%20Statement%20-%20Plane%20%232-Redacted.PDF - Pilot Interviews Summaries (item 8, .PDF, 219 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108459&FileExtension=.PDF&FileName=Pilot%20Interviews%20Summaries-Master.PDF - Notes from Interview by FAA Inspector with Passenger in Airplane #1 (item 9, .PDF, 158 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460061&FileExtension=.PDF&FileName=Notes%20from%20Interview%20by%20FAA%20Inspector%20with%20Passenger%20in%20Airplane%20%231-Redacted.PDF - Notes from Interview by FAA Inspector with Passenger in Airplane #2 (item 10, .PDF, 88 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460062&FileExtension=.PDF&FileName=Notes%20from%20Interview%20by%20FAA%20Inspector%20with%20Passenger%20in%20Airplane%20%232-Redacted.PDF - Wreckage Maps (item 11, .PDF, 890 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108462&FileExtension=.PDF&FileName=Wreckage%20Maps-Master.PDF - Hourly Weather Reports (item 12, .PDF, 58 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460063&FileExtension=.PDF&FileName=Hourly%20Weather%20Reports-Redacted.PDF - Weather Area Forecast (item 13, .PDF, 54 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460064&FileExtension=.PDF&FileName=Weather%20Area%20Forecast-Redacted.PDF - ATC Communication (item 14, .PDF, 66 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108465&FileExtension=.PDF&FileName=ATC%20Communication-Master.PDF - State Trooper Report (item 15, .PDF, 746 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108466&FileExtension=.PDF&FileName=State%20Trooper%20Report-Master.PDF - May 5, 1994 - FAA Form 337 Installing STOL Kit (item 16, .PDF, 110 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460065&FileExtension=.PDF&FileName=May%205,%201994%20-%20FAA%20Form%20337%20Installing%20STOL%20Kit-Redacted.PDF - Revision B - Feb 1993 Supplemental Type Certificate: Short Takeoff Landing Modification (item 17, .PDF, 217 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460066&FileExtension=.PDF&FileName=Revision%20B%20-%20Feb%201993%20Supplemental%20Type%20Certificate%3A%20Short%20Takeoff%20Landing%20Modification-Redacted.PDF - STC for STOL Kit - Revision D, March 1998 (item 18, .PDF, 279 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460067&FileExtension=.PDF&FileName=STC%20for%20STOL%20Kit%20-%20Revision%20D,%20March%201998-Redacted.PDF - Weight and Balance (item 19, .PDF, 260 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460068&FileExtension=.PDF&FileName=Weight%20and%20Balance-Redacted.PDF - Air Force DHC-2 Pilot Handbook Stall Performance (item 20, .PDF, 206 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108471&FileExtension=.PDF&FileName=Air%20Force%20DHC-2%20Pilot%20Handbook%20Stall%20Performance-Master.PDF - DHC-2 Civilian Pilot Handbook Stall Performance (item 21, .PDF, 153 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108472&FileExtension=.PDF&FileName=DHC-2%20Civilian%20Pilot%20Handbook%20Stall%20Performance-Master.PDF - U.S. Air Force Rescue Coordination Center Report (item 22, .PDF, 313 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108473&FileExtension=.PDF&FileName=U.S.%20Air%20Force%20Rescue%20Coordination%20Center%20Report-Master.PDF - Pilot Proficiency Check Flight (item 23, .PDF, 175 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460069&FileExtension=.PDF&FileName=Pilot%20Proficiency%20Check%20Flight-Redacted.PDF - Company Training Handbook - Stalls (item 24, .PDF, 41 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108475&FileExtension=.PDF&FileName=Company%20Training%20Handbook%20-%20Stalls-Master.PDF - Company Operations Manual - Flight Following Procedures (item 25, .PDF, 16 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108476&FileExtension=.PDF&FileName=Company%20Operations%20Manual%20-%20Flight%20Following%20Procedures-Master.PDF - Statement of Party Representatives to NTSB Investigation (item 26, .PDF, 41 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460070&FileExtension=.PDF&FileName=Statement%20of%20Party%20Representatives%20to%20NTSB%20Investigation-Redacted.PDF - Release of Aircraft Wreckage, NTSB Form 6120.15 (item 27, .PDF, 128 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460071&FileExtension=.PDF&FileName=Release%20of%20Aircraft%20Wreckage,%20NTSB%20Form%206120.15-Redacted.PDF - Toxicological Report (item 28, .PDF, 65 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40460072&FileExtension=.PDF&FileName=Toxicological%20Report-Redacted.PDF - Photo 1. View looking west towrad Telequana Pass. The canyon to the right contained the airplane wreckage. No Negative. (item 29, .PDF, 42 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108480&FileExtension=.PDF&FileName=Photo%201.%20%20View%20looking%20west%20towrad%20Telequana%20Pass.%20%20The%20canyon%20to%20the%20right%20contained%20the%20airplane%20wreckage.%20%20No%20Negative.-Master.PDF - Photo 2. View from the wreckage looking 150 degrees magnetic toward Telequana Pass. The lines are the estimated level of clouds as described by the pilot of the first two airplanes transiting the pass. (item 30, .PDF, 34 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108481&FileExtension=.PDF&FileName=Photo%202.%20%20View%20from%20the%20wreckage%20looking%20150%20degrees%20magnetic%20toward%20Telequana%20Pass.%20%20The%20lines%20are%20the%20estimated%20level%20of%20clouds%20as%20described%20by%20the%20pilot%20of%20the%20first%20two%20airplanes%20transiting%20the%20pass.-Master.PDF - Photo 3. View of wreckage. (item 31, .PDF, 34 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108482&FileExtension=.PDF&FileName=Photo%203.%20%20View%20of%20wreckage.-Master.PDF - Photo 4. Side view of wreckage. Note leading edge damage to right wing. (item 32, .PDF, 60 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108483&FileExtension=.PDF&FileName=Photo%204.%20%20Side%20view%20of%20wreckage.%20%20Note%20leading%20edge%20damage%20to%20right%20wing.-Master.PDF - Photo 5. View of Stall warning circuit breaker. (item 33, .PDF, 49 KB): https://data.ntsb.gov/Docket/Document/docBLOB?ID=40108484&FileExtension=.PDF&FileName=Photo%205.%20%20View%20of%20Stall%20warning%20circuit%20breaker.-Master.PDF 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.