Edmonton, Alberta, 24 November 2022 — Today, the Transportation Safety Board of Canada (TSB) released its investigation report (A21W0098) into the 2021 forced landing of an Air Tindi Ltd. de Havilland DHC-6-300 Twin Otter aircraft near Fort Providence, Northwest Territories (NWT), following fuel starvation. The investigation found that leading up to the event, there were several instances where checklists were not completed in accordance with company procedures.
On 01 November 2021, an Air Tindi Ltd. de Havilland DHC-6-300 Twin Otter aircraft departed Yellowknife Airport, NWT, on a visual flight rules flight to Fort Simpson Airport, NWT, with two flight crew and three passengers on board. Approximately 40 minutes into the flight, the crew realized that there was insufficient fuel to continue to Fort Simpson or to return to Yellowknife. The flight crew diverted the aircraft to Fort Providence Aerodrome and shut down the left engine to conserve fuel. Shortly after, the right engine flamed out. A forced landing onto muskeg was performed 6.7 nautical miles (14 km) northwest of Fort Providence Aerodrome. Approximately four hours after the forced landing, all occupants were recovered by rescue personnel. All occupants received minor injuries related to hypothermia. The aircraft sustained substantial damage.
The investigation determined that the aircraft had not been refuelled prior to departure. While conducting the Before Start checks from memory, the captain interrupted his routine by conversing with a passenger. Consequently, the fuel quantity check was missed and the preparation for flight continued without the captain being aware that the aircraft did not have sufficient fuel for the flight on board. While taxiing to the runway, the captain conducted the Taxi checks alone, silently, and from memory. Consequently, the fuel check on the checklist was missed and the aircraft departed with insufficient fuel for the flight. The first officer then completed the cruise checks silently and without reference to a checklist. As a result, the fuel state of the aircraft was not identified by either flight crew member.
A few of the experienced Air Tindi Ltd. DHC-6 captains within the company had developed the practice of performing some of the challenge and response checklists by memory only. This had become routine for most of their flights. Reporting is extremely important to a properly functioning safety management system (SMS). The investigation revealed that DHC-6 first officers who experienced deviations from company procedures tended to report informally rather than use the company SMS. As a result, company management, as a whole, was not fully aware of the deviation regarding checklist usage on the DHC-6 fleet, and did not have an opportunity to evaluate the risk and pursue a corrective action plan through the SMS. Safety management is an issue on TSB Watchlist 2022.
Following the occurrence, Air Tindi Ltd. enhanced checklist requirements and issued a company memo to flight crews emphasizing the requirement to follow all procedures and checklists. The company also enhanced fuelling procedures by requiring the captain to verify aircraft fuelling and sign an acknowledgement on every fuel slip before starting the engine. Flight crews are also required to communicate the fuel levels on board to the operations control centre before each departure.
See the investigation page for more information
The TSB is an independent agency that investigates air, marine, pipeline, and rail transportation occurrences. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.
Air Tindi Ltd.
de Havilland DHC-6-300 Twin Otter, C-GNPS
Fort Providence, Northwest Territories, 6.7 NM NW
01 November 2021
At 1748 Mountain Daylight Time on 01 November 2021, the Air Tindi Ltd. de Havilland DHC-6-300 Twin Otter aircraft (registration C-GNPS, serial number 558) departed Yellowknife Airport (CYZF), Northwest Territories, as flight TIN223, a visual flight rules flight to Fort Simpson Airport (CYFS), Northwest Territories, with 2 flight crew and 3 passengers on board.
Approximately 40 minutes into the flight, the flight crew realized that there was insufficient fuel to continue to CYFS or to return to CYZF. The flight crew diverted the aircraft to Fort Providence Aerodrome (CYJP), Northwest Territories, and informed the company of their decision. The left engine was intentionally shut down to conserve fuel. The right engine then flamed out.
A forced landing onto muskeg was performed at 1851 Mountain Daylight Time, 6.7 nautical miles (14 km) northwest of CYJP. A signal from the emergency locator transmitter was received by the Canadian Mission Control Centre shortly after. Approximately 4 hours after the forced landing, all occupants were recovered by rescue personnel. All occupants received minor injuries related to hypothermia. The aircraft sustained substantial damage.
1.0 Factual information
1.1 History of the flight
On 01 November 2021, the Air Tindi Ltd. (Air Tindi) de Havilland DHC-6-300 Twin Otter aircraft (registration C-GNPS, serial number 558) was scheduled to depart Yellowknife Airport (CYZF), Northwest Territories, at 1030Footnote1 to conduct the following 3 return flights under visual flight rules (VFR):
- The 1st return flight was from CYZF to Whatì Airport (CEM3), Northwest Territories: flight TIN218 out and flight TIN220 back.
- The 2nd return flight was from CYZF to Wekweètì Airport (CYWE), Northwest Territories: flight TIN212 out and flight TIN213 back.
- The 3rd return flight was from CYZF to CEM3: flight TIN220 out and flight TIN221 back.
Following those 3 return flights, the last trip of the day was flight TIN223 from CYZF to Fort Simpson Airport (CYFS), Northwest Territories (Figure 1; see Appendix A for greater detail). The same flight crew was to conduct all 7 flights and then overnight in Fort Simpson. This was the first time this flight crew had flown together. All flights consisted of a mix of passengers and cargo and were to be conducted under Canadian Aviation Regulations (CARs) Subpart 703 (Air Taxi Operations), except for flight TIN212, which was to be conducted under CARs Subpart 704 (Commuter Operations).Footnote2
During the last inbound flight of the day to CYZF (flight TIN221 on the day of the occurrence), it was typical for the flight crew to inform the flight coordinator how much fuel was required for the next flight. The flight coordinator would then place an order for fuel with the fuel company. The investigation was unable to confirm whether the flight crew had requested fuel from the flight coordinator for the occurrence flight; however, the flight coordinator did not call the fuel company with a fuel order. Flight TIN221 arrived at CYZF at 1725. The crew and passengers deplaned and entered the passenger boarding lounge. Then, the process of unloading and preparing for the last flight of the day (flight TIN223 to CYFS) began.
At 1738, the first officer returned to the aircraft from the passenger boarding lounge and began the external pre-flight inspection. Approximately 1 minute later, the captain returned to the aircraft and entered the cockpit through the front left door. While getting into his seat, the captain observed a fuel receipt in the door map pocket and assumed it was for the fuel he thought he had ordered for the flight to CYFS. He did not read the fuel receipt, which was from a flight 3 days prior.
Since landing, no fuel truck had arrived at the aircraft and consequently no fuel was added to the aircraft. According to the operational flight plan, the aircraft would have arrived in CYZF on flight TIN221 with approximately 533 pounds of fuel remaining. The operational flight plan for flight TIN223 to CYFS indicated that 2500 pounds of fuel were to be on board, which was standard for this flight.
The captain began preparing the aircraft for engine start by conducting the Before Start checks of the Air Tindi DHC6 Cockpit Checklist (Appendix B) using a geographic flow.Footnote3 At the same time, passengers started boarding the aircraft, and the captain interrupted the checks to converse with one of them with whom he used to work. After a short conversation, the captain resumed the checks.
At 1740, when passengers had finished boarding and the cargo had been loaded, the first officer briefed the passengers for the flight. The first officer then sat down in the cockpit and asked the captain if he would like to commence the Before Start checks. The captain declined and started the engines at 1743.
Unlike the first few legs of the day, the ensuing After Start, Taxi, and Line Up checks were completed by the captain from memory only. At 1747, the occurrence aircraft departed CYZF on flight TIN223, with the 2 pilots and 3 passengers on board. The aircraft climbed towards the planned cruising altitude of 6500 feet above sea level (ASL). The After Takeoff and Cruise checks were completed by the first officer without reference to the checklist. By this time in a typical flight, the flight crew would have been directed by Air Tindi DHC6 Cockpit Checkliston 3 separate occasions to observe the fuel quantity (see section 188.8.131.52 Checklists of this report).
At 1750, the fuel company at CYZF called the Air Tindi flight coordinator to ask whether the occurrence aircraft needed fuel. The flight coordinator informed the fuelling company that the aircraft was already airborne and on its way to CYFS.
Based on the fuel burn analysis (see section 1.16.1 Fuel quantity calculation of this report), the low-fuel-level caution light for the aft fuel tank illuminated at 1813. At this time, there were approximately 60 U.S. gallons of fuel left in the aircraft, including 8 U.S. gallons of fuel in the left-wing auxiliary tank and 9 U.S. gallons in the right-wing auxiliary tank. This would have given the aircraft about 40 minutes of flying time at cruise power before complete fuel exhaustion.
At 1826 (38 minutes after takeoff), when flight TIN223 was approximately halfway to CYFS, the flight crew noticed the illuminated low-fuel-level caution light for the aft fuel tank. The flight crew immediately realized that they had departed with insufficient fuel and began the process of determining where to divert to. It was decided that Fort Providence Aerodrome (CYJP), Northwest Territories, was the closest runway and, at 1829, flight TIN223 turned southbound towards it. During this time, the captain climbed the aircraft to 7000 feet ASL.
The captain informed the Air Tindi flight coordinator of the situation via the aircraft’s satellite radio. The flight coordinator relayed a suggestion from the chief pilot to consider shutting 1 engine down to conserve fuel, and the pilot agreed. At 1834, the captain began to draw fuel out of the auxiliary fuel tanks located in the wings,Footnote4 and the first officer briefed the passengers about the diversion. Shortly after, the captain commenced an intentional shutdown of the left engine and feathered the left propeller, which was completed at 1838. Power was then reduced on the right engine to conserve fuel and a slow descent was commenced. Fuel continued to be drawn from the right-wing auxiliary fuel tank. It was calculated during the investigation that an estimated 69 pounds of fuel remained in the forward fuel tank at this time and it is likely that the low-fuel-level caution light for the forward tank had illuminated.
At 1843, the captain noticed that the PUMP FAIL R TANK light had illuminated, indicating that the right-wing auxiliary fuel tank was nearly empty. The switch was then placed in the REFUEL position.
At 1847, flight TIN223 was about 11 nautical miles (NM) from CYJP, descending through 3300 feet ASL when the right engine began to surge. The flight crew shut down the engine and feathered the propeller, and the captain began slowing the aircraft to the optimal glide speed for maximum range of 86 knotsFootnote5 indicated airspeed. The first officer briefed the passengers for a forced approach to an off-airport landing. The captain looked for a suitable place to land. In the darkness, he was able to discern an area of muskeg and chose that area rather than a treed area.
Just before touchdown, the captain requested flaps to 10° and then full flap; the first officer selected those flap positions. The stall horn activated when the aircraft was just above the muskeg and seconds before touchdown. The aircraft touched down on the muskeg at 1851, 6.7 NM northwest of CYJP, and came to a stop in an upright position (Figure 2).
The Canadian Mission Control Centre, in Trenton, Ontario, received an emergency locator transmitter signal for the aircraft on frequency 406 MHz shortly after. Approximately 4 hours after the forced landing, all occupants were recovered by rescue personnel.
1.2 Injuries to persons
Two flight crew members and 3 passengers were on board the aircraft during the occurrence flight. All the occupants showed signs of and were treated for mild hypothermia. One passenger received a minor injury when walking out from the accident site.
|Degree of injury||Crew||Passengers||Persons not on board the aircraft||Total by injury|
1.3 Damage to aircraft
The aircraft remained upright during the landing and damage was limited to the nose bulkhead area at station 60. The nose landing gear was displaced rearward and there was associated wrinkling of nose skins and nose structure.
1.4 Other damage
There was no other damage.
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