Description

On 1 November 2021, a deHavilland DHC6-300 (C-GNPS) being operated by Air Tindi on a scheduled domestic passenger flight from Yellowknife to Fort Simpson as TIN223 departed without the crew checking the fuel quantity on board. En route they realised that it was not possible to reach the intended destination or any other airport and when fuel was exhausted, a forced landing was made in night VMC in a partly frozen treeless bog some 7 nm from Fort Providence. The aircraft sustained substantial damage but the five occupants sustained only minor injuries related to hypothermia. 

The aircraft where it finally stopped in the ‘muskeg’ (bog). [Reproduced from the Official Report]

Investigation

An Investigation was carried out by the Transportation Safety Board (TSB) of Canada. The 30 minute CVR was recovered and its data were successfully downloaded. However, its limited duration meant that only the period from the realisation of low fuel to the resulting forced landing was available. 

In this respect, the ICAO requirement announced in 2010 for CVRs “to retain the information recorded during at least the last 2 hours of their operation” with effect from 1 January 2016 had been deferred by Transport Canada until May 2023. It was noted that whilst the ICAO requirement in Annex 6 Part 1 was directly applicable only to international flights, Transport Canada’s significant deferral had resulted in Canadian operators continuing to conduct international flights using aircraft equipped with only 30-minute CVRs.    

It was also noted that since 01 January 2016, TSB Investigations have involved the downloading and analysis of data from 12 CVRs with only a 30-minute recording capacity with three of these investigations leading to a finding that they had been “hampered by insufficient data due to the 30-minute length of the CVR recording and a more complete understanding of the safety issues was not possible”.

The Flight Crew

The Training Captain in command of the accident flight had been PF and had a total of 6,396 hours flying experience of which 2,945 hours were on type. He had joined the operator 13 years previously initially as a ramp assistant and then as a flight coordinator. After almost three years in these roles, he “was trained and began to work as a First Officer on the deHavilland DHC6", transferring to the deHavilland DHC7 after two years and serving as a First Officer for a further four years before promotion to Captain on the company’s single engine, single pilot-operated nine passenger Cessna 208. After just over two years on the Cessna 208, he was upgraded to Captain on the DHC6 and after two years as a line pilot, he was approved by Air Tindi as a Line Training Captain on the type. The First Officer had been employed by Air Tindi six months prior to the accident and had been released to fly as a First Officer on the DHC6 two months prior to the accident. He had a total of 434 hours flying experience of which 84 hours were on type.

What Happened 

On the day of the accident, the aircraft and crew involved were rostered to operate three return flights from Yellowknife to nearby destinations in the North West Territories followed by a final flight to Fort Simpson for a night stop. It was the first time these two pilots had flown together. During an inbound flight, a crew would normally radio the duty flight coordinator to advise how much fuel was required for the next flight but it appears that this may not have happened. During a brief (just over 15 minute) turnround during which both pilots briefly went into the terminal, they returned with the First Officer carrying out the external pre flight inspection and the Captain getting into the flight deck via the direct access left hand door. Whilst doing so, he reported having seen a fuel receipt in the door map pocket which he did not read and “assumed it was for the fuel he thought he had ordered” for the imminent flight. In fact it was from a flight which had taken place three days earlier.

No fuel bowser had arrived at the aircraft during the turnround and consequently no fuel was uplifted. According to the OFP, the fuel on arrival from the previous flight was likely to have been around 180 kg and the OFP for the final sector showed that it was intended to depart with 1135 kg in tanks which was a standard figure for the sector concerned. The Captain began the Before Start Checks whilst the three passengers were boarding and briefly interrupted the checks to speak with one of them he knew.

Once loading of cargo and passengers was complete, the First Officer, having completed his external inspection, then presented the passenger safety brief before returning to the flight deck and asking the Captain if he would like to run the Before Start checks but the offer was declined and the Captain started the engines. In apparent contrast to some of the earlier flights, subsequent After Start, Taxi, and Line Up checks were all completed by the Captain from memory and three minutes after starting the engines, the flight departed. Three minutes after this, the Yellowknife fuel company called the Air Tindi flight coordinator to ask if the aircraft needed fuel to which the latter replied that the aircraft was already airborne and on the way to Fort Simpson. 

After becoming airborne, the aircraft climbed to the planned cruise altitude of 6500 feet QNH. The First Officer completed the After Takeoff and Cruise Checks without use of the corresponding checklists. It was noted that “by this time in a typical flight”, the pilots would have been directed on three separate occasions by the Checklist to check the fuel quantity. It was estimated by the Investigation that the fuel low caution light for the aft fuel tank had illuminated 26 minutes after departure with around 180 kg of fuel left on board the aircraft including 24 kg in the left wing auxiliary tank and 27 kg in the right wing auxiliary tank. It was estimated that this would have given the aircraft about 40 minutes of flying time at cruise power before complete fuel exhaustion. However, it appeared that this caution annunciation went unnoticed by the crew until 12 minutes later when the fight was approximately halfway to Fort Simpson. 

At this point, the pilots reported immediately realising that they had departed with insufficient fuel and began the process of determining where to divert to, deciding that the nearest runway was at Fort Providence, to which course was altered three minutes later. The Captain decide to climb the aircraft to 7000 feet QNH and then advised the company of the situation via SATCOM upon which a message from the Chief Pilot was relayed with the suggestion to shut one engine down to conserve fuel which the Captain decided to do.

Five minutes after beginning the diversion, the Captain began to draw fuel from the auxiliary wing tanks and the First Officer briefed the passengers about the diversion. Shortly afterwards, the Captain completed intentional shutdown of the left engine and feathered the left propeller. Power on the right engine was then reduced to conserve fuel and a slow descent was commenced using fuel drawn from the right wing auxiliary and forward fuel tanks. It was estimated that at that time, approximately 31 kg of fuel remained in the forward tank and it was therefore likely that the low fuel caution light for the forward tank had also illuminated. 

Fourteen minutes after beginning the diversion, the Captain was recorded noticing that the ‘PUMP FAIL R TANK’ light had illuminated, which indicated that the right wing auxiliary tank was nearly empty. The switch was then placed in the REFUEL position. 

The wing fuel tank panel after the accident. [Reproduced from the Official Report]

Four minutes after this, with the flight approximately 11 nm from Fort Providence and descending through 3,300 feet QNH, the right engine began to surge and it was shut down and the propeller feathered as the Captain began to reduce to the optimal glide speed for maximum range of 86 KAIS. The First Officer briefed the passengers for a forced off-airport landing and despite the darkness, the Captain was able to identify an area free of trees and continued to a landing after 25 minutes airborne. The aircraft came to a stop in a partially frozen bog (known locally as ‘muskeg’) in an upright position which contributed to the main damage being limited to the nose landing gear and bulk and wrinkling of the forward fuselage skin. An ELT signal on 406 MHz was automatically transmitted and rescue services reached the location after four hours and recovered all occupants from the aircraft.

Why It Happened

It was confirmed that there had been no abnormalities in the aircraft airframe or malfunctions in the engine fuel supply systems. It was noted that whilst the quantity of remaining fuel meant that reaching Fort Providence was possible, this possibility no longer existed once the management of the remaining fuel was not been optimal. 

It was noted that when the left engine had been shut down, fuel was being drawn from the left-wing tank and that after this shutdown, 5 U.S. gallons of fuel had remained in this tank. With the left engine shut down and its associated fuel pump off, this fuel would only have been available to the right engine if the fuel system had been appropriately reconfigured. When, five minutes after the left engine shutdown, the ‘PUMP FAIL R TANK’ indication had illuminated, it was calculated that only around 1 U.S. gallon of fuel would have remained in that tank at this time.

It was considered that when the Captain intended to select the right wing fuel tank switch from the ‘ENGINE’ to the ‘OFF’ position to enable the engine to be fed from the forward main fuel tank, he probably went through the ‘OFF’ position to the ‘REFUEL’ position which “rather than feeding the right engine...would have transferred fuel from the forward main tank to the right wing tank” which would be consistent with the 7 U.S. gallons of fuel found in the right tank after the forced landing. Correctly configured, the fuel system could have transferred the remaining 6 U.S. gallons from the main fuel tank to the right wing tank in the 4 minutes before the right engine flamed out. It was also noted that with the fuel selector inadvertently in the ‘REFUEL’ position, fuel left in the tank when the engine was shutdown was not available to the remaining operating engine. Finally, it was noted that there is no flight deck indication when ‘REFUEL’ has been selected (although the AFM explicitly prohibits refuelling in flight).    

As regards the failure to properly perform normal checklists which would have identified the lack of intended fuel loading prior to departure, it was found during the Investigation that some of the junior First Officers at Air Tindi including the accident First Officer “were aware and had discussed amongst themselves that when flying with some of the senior Captains, these Captains had adopted the practice of performing some of the verbal challenge and response checklists silently, by memory only and by themselves, i.e., without necessarily the input or challenge from their First Officer”. It was noted that some of these senior Captains had been First Officers with the airline prior to promotion to command. The accident First Officer and others had “accommodated this practice without any safety reports being submitted to the company (although) they had informally discussed this checklist practice with some of the DHC6 Training Captains”. Company management claimed to be “not fully aware of the issue” but First Officers stated that they were “aware that the company was passing these senior Captains during Check Flights and permitting them to continue flying”. The Investigation “determined that DHC6 captains were performing in accordance with SOPs during their Check flights”. Given the finding that no SMS reports had ever been filed in respect of checklist usage or fuel for the DHC6 fleet, it was impossible not to conclude that whilst the Air Tindi SMS was approved, in practice it was dysfunctional. 

Seven Findings as to Causes and Contributing Factors were formally recorded as follows:

1. When the Captain saw the pink fuel slip in the door of the aircraft, it reinforced his belief that the aircraft had been fuelled for the last flight of the day, when, in actuality, it had not been refuelled.
2. 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.
3. Over time, the Captain (had) developed an adaptation of not conducting the challenge and response checklists where required by the standard operating procedures. The absence of negative consequences reinforced the Captain’s practice until it became routine. 
4. On the day of the occurrence, the First Officer’s adaptation regarding checklist usage was influenced by the seniority of the Captain, the Captain’s non-standard use of checklists, and the absence of negative repercussions from this adaptation. 
5. 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. 
6. The First Officer 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 pilot.
7. As a result of fuel starvation, the flight crew conducted a forced landing into muskeg, which resulted in significant aircraft damage.  

Five Findings as to Risk were also formally recorded as follows: 

1. If flight crews do not maintain a scan of the flight instrument panel and alerting systems, there is a risk that they will not identify an abnormal aircraft state that escalates to an unsafe situation.
2. If flight crews do not refer to performance charts when attempting to fly for maximum range, an inappropriate power setting and aircraft configuration may be selected and maximum range may not be achieved.
3. The DHC-6 wing fuel tank switch is designed such that it can be moved to the ‘REFUEL’ position in flight, increasing the risk of inadvertent transfer of fuel from the main fuel tank to the respective wing fuel tank.
4. If flight crews descend rather than maintain altitude in fuel-critical situations where a possibility of fuel exhaustion is likely, the aircraft’s gliding distance will be reduced, increasing the risk of landing on unsuitable terrain.
5. If flight crews do not use the company reporting procedures to communicate safety concerns related to operational deviations, there is a risk that company management will be unaware of unsafe practices and unable to take corrective action.  

Two Other Findings were also formally recorded:

1. The aircraft fuel quantity indication and alerting systems were functional and performed as designed. There were no leaks or abnormalities in the aircraft airframe or engine fuel systems. 
2. The aircraft landed with a total of 36 kg of usable fuel, 6.7 nautical miles from Fort Providence Airport. This amount of fuel was sufficient for approximately 8 minutes of flight at cruise speed, or a range of about 20 nautical miles.  

Safety Action taken by Air Tindi was noted as including revision of their ‘challenge – response’ requirement for checklists to become a ‘challenge - response – verification’ requirement. 

The Final Report of the Investigation was authorised for release on 19 October 2022 and it was officially released on 24 November 2022. No Safety Recommendations were made.  

Related Articles

• Controlled Flight Into Terrain (CFIT)
• Fuel - Preflight Planning
• Fuel - In-Flight Management (Abnormal Operations)
• Fuel Starvation
• Standard Operating Procedures (SOPs)
• Checklists - Purpose and Use
• Complacency
• Authority Gradients
• Regulatory Oversight