Tindi DHC6 near Ft. Providence on Nov 1st 2021, forced landing outside airport due to running out of fuel
Last Update: November 24, 2022 / 18:16:36 GMT/Zulu time
Incident Facts
Date of incident
Nov 1, 2021
Classification
Accident
Airline
Air Tindi
Flight number
8T-223
Departure
Yellowknife, Canada
Destination
Fort Simpson, Canada
Aircraft Registration
C-GNPS
Aircraft Type
De Havilland DHC-6 Twin Otter
ICAO Type Designator
DHC6
The TSB reported, the passengers and crew were recovered about 8 hours after the forced landing. The occurrence was rated an accident and a class 3 investigation has been opened.
The company reported the aircraft ran out of fuel. The crew reported a malfunction of the aircraft while still airborne and diverting to Fort Providence, about 2-3 minutes prior to estimated landing the crew realized they won't make it to the runway. They then lost contact with the crew for about 15 minutes, then the crew called again. The cause of why the aircraft ran out of fuel is under investigation.
The volunteer fire fighting department of Fort Providence reported the aircraft looked fairly intact commenting a normal aircraft had landed in a swamp. The aircraft came to rest in swampland covered by a couple of inches of ice which broke under the aircraft. The water was about two feet deep. They were able to walk to the aircraft though and take the occupants to safety in night conditions across the swamp reassuring the occupants there was hot coffee and warmth awaiting them.
On Nov 13th 2021 the TSB opened their investigation page, provided information about the final location of the aircraft and stated: "Approximately 40 minutes into the flight, the flight crew diverted to Fort Providence Airport, Northwest Territories. At 1847, a forced landing was performed 6.7 nautical miles northwest of Fort Providence Airport. The occupants were rescued approximately 5 hours after the forced landing. There were no injuries." (Editorial note: based on the map provided by the TSB it is obvious the 6.7nm are to the village of Fort Providence, but 8.5nm to the airport).
On NOv 24th 2022 the TSB released their final report concluding the probable causes were:
Findings as to causes and contributing factors
- 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.
- 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.
- Over time, the captain 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.
- 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.
- 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 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.
- As a result of fuel starvation, the flight crew conducted a forced landing into muskeg, which resulted in significant aircraft damage.
Findings as to risk
- 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.
- 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.
- 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.
- 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.
- 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.
Other findings
- 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.
- The aircraft landed with a total of 12 U.S. gallons of usable fuel, 6.7 nautical miles from the Fort Providence Aerodrome. This amount of fuel was sufficient for approximately 8 minutes of flight at cruise speed, or a range of about 20 nautical miles.
The TSB analysed:
While on the inbound flight to Yellowknife Airport (CYZF) on the second-last leg of the day, the flight crew likely did not request fuel through the flight coordinator, even though they typically had done so in the past. When the captain entered the aircraft to prepare for the last flight of the day, he observed a pink fuel slip in the door and assumed it was for the fuel that he thought he had ordered for the flight.
The captain then performed the Before Start checks from memory, as allowed by company standard operating procedures (SOPs). Fuel quantity is checked as one of the items on this checklist. As he was completing this check, passengers began boarding the aircraft. The captain conversed with one of the passengers who used to work with him. After the short conversation, the captain resumed the checks, but did not note that the fuel quantity was insufficient for the planned flight.
Checklist usage adaptations
Captain
Flight crew checklists prompt pilots to perform specific tasks, reducing the probability that they omit a safety critical step. At Air Tindi, checklists that contain the most critical items for flight safety are performed using the challenge and response technique. The technique increases the probability of detecting any omissions because when checklist items are read aloud by one pilot and responded to by the other pilot, omissions are more likely to be avoided. However, to be effective, the operating culture and crew resource management practices must encourage and reinforce the routine use of challenge and response checklists.
The occurrence captain, along with a few of the other experienced captains within the company, had developed the practice of performing some of the challenge and response checks silently, by memory only, and by themselves. This adaptation was perceived as more efficient. The lack of negative repercussions each time this adaptation occurred likely reinforced the captain’s decision to continue with this practice until it became a normal part of his routine.
First officer
The day of the occurrence was the first time that the first officer and captain had flown together. At the start of the day’s first flight, the first officer expected operations to proceed per the SOPs, i.e., checks would be performed as required by both pilots, and they did.
However, as the flights progressed throughout the day, the first officer soon recognized the captain’s adaptations. Although the captain did not prohibit the first officer from performing any checklist activity, the first officer became progressively more passive. This further increased the probability that omissions would not be detected. This passiveness was likely the result of the first officer being influenced in general by:
- the knowledge that other first officers were aware of such adaptations and that they tolerated them; and
- other captains with whom the first officer flew also did not routinely use checklists.
The first officer was also influenced on this particular day by:
- the fact that the company continued to approve the captain;
- the comparative seniority of the captain; and
- the fact that the captain had completed other tasks without checklists without any apparent repercussions.
Specifically, it is likely there was a normative influence, driven by the expectations of others.
The first officer was influenced by the non-standard use of checklists by this captain as well as other captains, and followed that behaviour because he perceived it to be the norm and that it would be socially preferred.
Taxi and takeoff
The aircraft had not been refuelled before takeoff. While taxiing for takeoff, the captain completed the Taxi checks on his own from memory, rather than by verbal challenge and response with the first officer. While doing the checks, he omitted to check the fuel gauge and therefore did not notice that the aircraft had not been fuelled to the planned 2500 pounds, which was standard for this flight. The first officer had adopted a more passive role in the cockpit and did not perform a mental checklist including checking the fuel gauge. As a result, he did not detect the captain’s omission.
Climb and cruise
During the initial climb, the After Takeoff checks are normally performed by the pilot monitoring. On the occurrence flight, these checks were completed by the first officer silently and without reference to the checklist. Once the aircraft reached cruise, the Cruise checks were completed by the first officer and, once again, they were done silently rather than by verbal action and confirmation. This was the last opportunity for both the captain and the first officer to realize that there was insufficient fuel for the flight.
The low-fuel-level caution light for the aft fuel tank illuminated about 25 minutes after the aircraft took off from CYZF. At this time, there were approximately 60 U.S. gallons of fuel left in the aircraft, including the wing fuel tanks, which gave the aircraft about 40 minutes of flying time before complete fuel exhaustion. However, the flight crew did not observe the AFT FUEL LOW LEVEL light for another 13 minutes, at which point approximately 28 minutes of fuel remained.
Diversion
Flight for maximum range
When the flight crew became aware that fuel quantity was an issue, a diversion was started toward Fort Providence Aerodrome (CYJP) and engine power was reduced to conserve fuel.
No performance charts were consulted to determine what the ideal power setting would have been to achieve the maximum distance for the amount of fuel remaining (flight for maximum range). The abnormal procedures checklist for FUEL LOW LEVEL light does not provide guidance to refer to performance charts for a low fuel situation and indicates only that there is approximately 15 minutes of fuel remaining if both low level lights are illuminated.
Intentional left-engine shutdown
While diverting to CYJP, the captain communicated with Air Tindi via the satellite telephone.
During one of the communications, it was suggested that he shut 1 engine down to conserve fuel. This suggestion originated from the chief pilot through the flight coordinator.
The DHC-6 aircraft flight manual provides performance figures on single-engine cruise fuel consumption per nautical mile. These numbers indicate that at 7000 feet above sea level (ASL) and an aircraft weight of 9000 pounds, with the remaining engine set to maximum continuous power, the fuel consumption per nautical mile would be 21% less if the flight was continued on 1 engine rather than 2.
Neither the flight crew nor the chief pilot consulted these charts during the occurrence flight; however, given the limited time available, this may not have been practical. Given that the engine shutdown was followed by a gradual descent at a single-engine power setting below maximum continuous power, it could not be determined to what extent the intentional shutdown affected the remaining range.
DHC-6-300 fuel system
When the left engine was shut down, fuel was being drawn from the left-wing tank. After the left engine shutdown, 5 U.S. gallons of fuel remained in the left-wing fuel tank. With the left engine shut down and the associated fuel pump off, this fuel was unavailable to the right engine unless the flight crew reconfigured the fuel system. Five minutes later, the flight crew noticed that the PUMP FAIL R TANK light had illuminated, indicating that the quantity was getting low. It was calculated that there would have been about 1 U.S. gallon in that right-wing tank at this time.
When the captain moved the right wing fuel tank switch from ENGINE to OFF, to return to feeding the right engine from the forward main fuel tank, he likely went through the OFF position to the REFUEL position. Rather than feeding the right engine, this setting would have transferred fuel from the forward main tank to the right-wing fuel tank, which is consistent with the 7 U.S. gallons of fuel found in the right tank after the forced landing. The fuel system could have transferred 6 U.S. gallons from the main fuel tank to the wing tank in the 4 minutes before the right engine flamed out. Additionally, with the switch in the REFUEL position, fuel from the right-wing fuel tank was not available to the right engine.
There are no cockpit indications when REFUEL has been selected. Although the aircraft flight manual prohibits refuelling in flight, there are no defenses in place to prevent the switch from being placed in the REFUEL position.
Forced approach to an off-airport landing
The right engine flamed out owing to there being insufficient fuel in the forward main fuel tank. The aircraft was 11.8 NM from CYJP and was at 2800 feet above ground level. The aircraft was flown in the best configuration for maximum glide distance and glided 5.1 NM during the descent. The descent started (6500 feet above ground) after the intentional leftengine shutdown, placing the aircraft 3700 feet lower when the right engine failed. This extra 3700 feet would have resulted in about 6.5 NM of extra glide range.
Company safety management system
To be aware of developing issues within a company, reporting is extremely important to a properly functioning safety management system (SMS). The reporting function of the Air Tindi SMS was established and being used often. The investigation revealed that DHC-6 first officers who experienced deviations from company SOPs tended to report informally to the training captains rather than use the SMS. As a result, company management, as a whole, was not fully aware of the deviation from SOPs 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.
Aircraft Registration Data
Aircraft registration data reproduced and distributed with the permission of the Government of Canada.
Incident Facts
Date of incident
Nov 1, 2021
Classification
Accident
Airline
Air Tindi
Flight number
8T-223
Departure
Yellowknife, Canada
Destination
Fort Simpson, Canada
Aircraft Registration
C-GNPS
Aircraft Type
De Havilland DHC-6 Twin Otter
ICAO Type Designator
DHC6
This article is published under license from Avherald.com. © of text by Avherald.com.
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