An Air Inuit de Havilland Dash 8-300, registration C-GAIW performing freight flight 3H-885 from La Grande Riviere,QC to Kangiqsujuaq,QC (Canada) with 3 crew, landed on Kangiqsujuaq's runway 15 but touched down short of the runway causing substantial damage to the left main landing gear. The aircraft bounced, touched down a second time on right main and nose gear, the crew managed to regain directional control and stopped the aircraft on the runway. The aircraft received substantial damage, the left main gear wheels and lower section separated.
Canada's TSB released their final report concluding the probable causes of the accident were:
- To minimize the risk of a runway overrun, the pilot was flying as he normally would for this type of operation, aiming to land near the runway threshold. He used an area just beyond the runway threshold as the aiming point and was visually following a descent angle of 3°. As a result, the aircraft was flying below the glide path on a trajectory where the wheels were going to touch down approximately 228 feet before the threshold if the descent was not stopped.
- Using an area just beyond the threshold as an aiming point placed the aircraft on a descent path leading to a touchdown before the runway threshold. The descent was not stopped owing to the effects of a downdraft. As a result, the touchdown occurred approximately 220 feet before the threshold, the wheels struck the mound below the runway level, and the left landing gear fractured.
Other Finding
In this occurrence, although the aircraft was flying below the glide path, the captain was aware of possible illusions at this location and visually maintained a constant descent angle of 3 degrees.
The TSB analysed:
The investigation did not reveal any signs of an aircraft system, airframe, or engine failure that may have been a contributing factor in the occurrence flight. Furthermore, the aircrafts performance was not considered to be a contributing factor. The flight crew held the appropriate licences and ratings for the flight, and there was no indication that the flight crews performance was degraded by fatigue or medical factors.
In this occurrence, the pilot flew as he normally would and brought the aircraft below the glide path to aim for a landing closer to the runway threshold. The analysis will therefore focus on this approach practice, including the descent below the glide path, the aiming point used, and the effects of the terrain and environmental conditions specific to Kangiqsujuaq (Wakeham Bay) Airport (CYKG).
Descent below the glide path and aiming point
During the visual portion of a final approach, pilots fix their gaze on a specific aiming point on the runway. When there are no aiming points or touchdown markings, pilots tend to aim for the threshold to touch down as soon as possible on gravel runways, which are susceptible to reduced braking effectiveness in the winter. This practice is meant to reduce the risk of a runway overrun. The investigation determined that this practice was widespread in operations on gravel runways shorter than 4000 feet.
Several factors could explain this practice, which is used to maximize the distance available for the ground roll during landing. The manufacturers landing performance calculations for this type of aircraft are based on an aircraft crossing the threshold at a height of 50 feet and touching down in the next 840 to 1050 feet. As a result, on a 3520-foot-long gravel runway like the one at CYKG, touchdown occurs in the last quarter of the touchdown zone. Pilots may have the impression that this distance between the threshold and touchdown is somehow lost for the ground roll, thereby reducing the safety margin for avoiding a runway overrun.
Air Inuit had published in its standard operating procedures a best practice based on Transport Canadas TP 312 and the Transport Canada Aeronautical Information Manual (TC AIM). This practice recommended using the wind direction indicator as an aiming point for runways like the one at CYKG to allow for a touchdown from 500 feet beyond the runway threshold. As with the aircraft manufacturers calculations, pilots may have the impression that this distance is also lost for the ground roll, limiting the safety margin.
At Air Inuit, pilots had only the factored landing distances available in their flight planning documents. These distances, which are calculated during flight preparation and include a safety margin, are longer than the distance indicated in the aircraft flight manual. Furthermore, factored distances include the part of the distance when the aircraft is still airborne after crossing the runway threshold; this distance is unknown to the pilots. For this flight, the factored distance was calculated to be 3170 feet, which is only 350 feet less than the length of the runway (3520 feet). This information may have maintained the flight crews impression that they had only a small safety margin, especially with the changing runway conditions.
The TSB has previously identified the risks associated with a low approach that has an aiming point close to the runway threshold. In Aviation Investigation Report A12Q0161, the TSB indicated that if pilots descend below the optimum approach slope of 3°, there is an increased risk of collision with obstacles during approach and of landing short of the runway.
In this occurrence, the captain intended to perform a flare so that the aircraft would touch down after the runway threshold lights.
Effect of the terrain and environmental conditions on the approach
CYKG is located in an area with rocky, uneven terrain. The approach area is subject to downdrafts. At the end of the approach, the negative wind reading detected by the flight data recorder (FDR) confirms that the aircraft encountered a downdraft, which began pushing it toward the ground. The captain reacted by pitching the aircrafts nose up and increasing power. When the aircraft was 5.5° nose up, the landing gear was approximately 12 feet lower than the pilots eyes. Even though this manoeuvre was successful in slowing down the inadvertent descent, it did not stop the descent and was not enough to prevent a touchdown before the start of the runway.
At CYKG, when the runway was built, the uneven terrain needed to be levelled at the top of the hill, creating a mound of gravel approximately 220 feet before the threshold. When the aircraft struck this mound, the left wheel touched the ground approximately 5 inches below the runway level, and the right wheel, approximately 4 inches below this level. This contact resulted in an overstress fracture in the left landing gear strut, and the strut detached from the wheel assembly.
Canada's TSB released their final report concluding the probable causes of the accident were:
- To minimize the risk of a runway overrun, the pilot was flying as he normally would for this type of operation, aiming to land near the runway threshold. He used an area just beyond the runway threshold as the aiming point and was visually following a descent angle of 3°. As a result, the aircraft was flying below the glide path on a trajectory where the wheels were going to touch down approximately 228 feet before the threshold if the descent was not stopped.
- Using an area just beyond the threshold as an aiming point placed the aircraft on a descent path leading to a touchdown before the runway threshold. The descent was not stopped owing to the effects of a downdraft. As a result, the touchdown occurred approximately 220 feet before the threshold, the wheels struck the mound below the runway level, and the left landing gear fractured.
Other Finding
In this occurrence, although the aircraft was flying below the glide path, the captain was aware of possible illusions at this location and visually maintained a constant descent angle of 3 degrees.
The TSB analysed:
The investigation did not reveal any signs of an aircraft system, airframe, or engine failure that may have been a contributing factor in the occurrence flight. Furthermore, the aircrafts performance was not considered to be a contributing factor. The flight crew held the appropriate licences and ratings for the flight, and there was no indication that the flight crews performance was degraded by fatigue or medical factors.
In this occurrence, the pilot flew as he normally would and brought the aircraft below the glide path to aim for a landing closer to the runway threshold. The analysis will therefore focus on this approach practice, including the descent below the glide path, the aiming point used, and the effects of the terrain and environmental conditions specific to Kangiqsujuaq (Wakeham Bay) Airport (CYKG).
Descent below the glide path and aiming point
During the visual portion of a final approach, pilots fix their gaze on a specific aiming point on the runway. When there are no aiming points or touchdown markings, pilots tend to aim for the threshold to touch down as soon as possible on gravel runways, which are susceptible to reduced braking effectiveness in the winter. This practice is meant to reduce the risk of a runway overrun. The investigation determined that this practice was widespread in operations on gravel runways shorter than 4000 feet.
Several factors could explain this practice, which is used to maximize the distance available for the ground roll during landing. The manufacturers landing performance calculations for this type of aircraft are based on an aircraft crossing the threshold at a height of 50 feet and touching down in the next 840 to 1050 feet. As a result, on a 3520-foot-long gravel runway like the one at CYKG, touchdown occurs in the last quarter of the touchdown zone. Pilots may have the impression that this distance between the threshold and touchdown is somehow lost for the ground roll, thereby reducing the safety margin for avoiding a runway overrun.
Air Inuit had published in its standard operating procedures a best practice based on Transport Canadas TP 312 and the Transport Canada Aeronautical Information Manual (TC AIM). This practice recommended using the wind direction indicator as an aiming point for runways like the one at CYKG to allow for a touchdown from 500 feet beyond the runway threshold. As with the aircraft manufacturers calculations, pilots may have the impression that this distance is also lost for the ground roll, limiting the safety margin.
At Air Inuit, pilots had only the factored landing distances available in their flight planning documents. These distances, which are calculated during flight preparation and include a safety margin, are longer than the distance indicated in the aircraft flight manual. Furthermore, factored distances include the part of the distance when the aircraft is still airborne after crossing the runway threshold; this distance is unknown to the pilots. For this flight, the factored distance was calculated to be 3170 feet, which is only 350 feet less than the length of the runway (3520 feet). This information may have maintained the flight crews impression that they had only a small safety margin, especially with the changing runway conditions.
The TSB has previously identified the risks associated with a low approach that has an aiming point close to the runway threshold. In Aviation Investigation Report A12Q0161, the TSB indicated that if pilots descend below the optimum approach slope of 3°, there is an increased risk of collision with obstacles during approach and of landing short of the runway.
In this occurrence, the captain intended to perform a flare so that the aircraft would touch down after the runway threshold lights.
Effect of the terrain and environmental conditions on the approach
CYKG is located in an area with rocky, uneven terrain. The approach area is subject to downdrafts. At the end of the approach, the negative wind reading detected by the flight data recorder (FDR) confirms that the aircraft encountered a downdraft, which began pushing it toward the ground. The captain reacted by pitching the aircrafts nose up and increasing power. When the aircraft was 5.5° nose up, the landing gear was approximately 12 feet lower than the pilots eyes. Even though this manoeuvre was successful in slowing down the inadvertent descent, it did not stop the descent and was not enough to prevent a touchdown before the start of the runway.
At CYKG, when the runway was built, the uneven terrain needed to be levelled at the top of the hill, creating a mound of gravel approximately 220 feet before the threshold. When the aircraft struck this mound, the left wheel touched the ground approximately 5 inches below the runway level, and the right wheel, approximately 4 inches below this level. This contact resulted in an overstress fracture in the left landing gear strut, and the strut detached from the wheel assembly.
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