Air Canada A320 at Halifax on Mar 29th 2015, touched down short of runway
Last Update: May 18, 2017 / 14:01:56 GMT/Zulu time
Findings as to causes and contributing factors
- Air Canada's standard operating procedure (SOP) and practice when flying in flight path angle guidance mode was that, once the aircraft was past the final approach fix, the flight crews were not required to monitor the aircraft's altitude and distance from the threshold or to make any adjustments to the flight path angle. This practice was not in accordance with the flight crew operating manuals of Air Canada or Airbus.
- As per Air Canada's practice, once the flight path angle was selected and the aircraft began to descend, the flight crew did not monitor the altitude and distance from the threshold, nor did they make any adjustments to the flight path angle.
- The flight crew did not notice that the aircraft had drifted below and diverged from the planned vertical descent angle flight profile, nor were they aware that the aircraft had crossed the minimum descent altitude further back from the threshold.
- Considering the challenging conditions to acquire and maintain the visual cues, it is likely the flight crew delayed disconnecting the autopilot until beyond the minimum descent altitude because of their reliance on the autopilot system.
- The approach and runway lights were not changed from setting 4 to setting 5; therefore, these lights were not at their maximum brightness setting during the approach.
- The system to control the airfield lighting's preset selections for brightness setting 4 was not in accordance with the NAV CANADA Air Traffic Control Manual of Operations requirement for the omnidirectional approach lighting system to be at its brightest settings.
- The limited number of visual cues and the short time that they were available to the flight crew, combined with potential visual illusions and the reduced brightness of the approach and runway lights, diminished the flight crew's ability to detect that the aircraft's approach path was taking it short of the runway.
- The flight crew's recognition that the aircraft was too low during the approach would have been delayed because of plan continuation bias.
- The aircraft struck terrain approximately 740 feet short of the runway threshold, bounced twice, and then slid along the runway before coming to a rest approximately 1900 feet beyond the runway threshold.
- At some time during the impact sequence, the captain's head struck the glare shield because there were insufficient acceleration forces to lock the shoulder harness and prevent movement of his upper body.
- The first officer sustained a head injury and serious injury to the right eye as a result of striking the glare shield because the automatic locking feature of the right-side shoulder-harness inertia reel was unserviceable.
- A flight attendant was injured by a coffee brewer that came free of its mounting base because its locking system was not correctly engaged.
- Because no emergency was expected, the passengers and cabin crew were not in a brace position at the time of the initial impact.
- Most of the injuries sustained by the passengers were consistent with not adopting a brace position.
Findings as to risk
- If aircraft cockpit voice recorder installations do not have an independent power supply, additional, potentially valuable information will not be available for an investigation.
- If Transport Canada does not consistently follow its protocol for the assessment of aeromedical risk and ongoing surveillance in applicants who suffer from obstructive sleep apnea, some of the safety benefit of medical examinations will be lost, increasing the risk that pilots will fly with a medical condition that poses a risk to safety.
- If new regulations on the use of child-restraint systems are not implemented, lap-held infants and young children are exposed to undue risk and are not provided with a level of safety equivalent to that for adult passengers.
- If passengers do not dress appropriately for safe travel, they risk being unprepared for adverse weather conditions during an emergency evacuation.
- If the type of approach lighting system on a runway is not factored into the minimum visibility required to carry out an approach, in conditions of reduced visibility, the lighting available risks being less than adequate for flight crews to assess the aircraft's position and decide whether or not to continue the approach to a safe landing.
- If they do not incorporate a means of absorbing forces along their longitudinal axis, vertically mounted, non-structural beams (channels, tubes, etc.) in cargo compartments could penetrate the cabin floor when the fuselage strikes the water or ground, increasing the risk of aircraft occupants being injured or emergency egress being impaired.
- If an aircraft manufacturer's maintenance instructions do not include the component manufacturer's safety-critical test criteria, the component risks not being maintained in an airworthy condition.
- If there is a complete loss of electrical and battery power and the passenger address system does not have an independent emergency power supply, the passenger address system will be inoperable, and the initial command to evacuate or to convey other emergency instructions may be delayed, putting the safety of passengers and crew at risk.
- If passengers retrieve or attempt to retrieve their carry-on baggage during an evacuation, they are putting themselves and other passengers at a greater risk of injury or death.
- If passengers do not pay attention to the pre-departure safety briefings or review the safety-features cards, they may be unprepared to react appropriately in an accident, increasing their risk of injury or death.
- If an organization's emergency response plan does not identify all available transportation resources, there is an increased risk that evacuated passengers and crew will not be moved from an accident site in a timely manner.
- If organizations do not practise transporting persons from an on-airport accident site, they may be insufficiently prepared to react appropriately to an actual accident, which may increase the time required to evacuate the passengers and crew.
- The service director assessed the evacuation flow as good and determined that there was therefore no need to open the R1 door.
- The flight attendants stationed in the rear of the aircraft noted no life-threatening hazards. Because no evacuation order had been given, and deplaned passengers and firefighters were observed walking near the rear of the aircraft in an area where the deployment of the rear slides may have created additional hazards or risks, the flight attendants determined that there was no requirement to open the L2 and R2 doors.
- Although Transport Canada required the dual-exit drill to be implemented in training, it did not require all cabin crew to receive the training before an organization implemented the 1:50 ratio.
- At the time of the accident, neither the service director nor the flight attendants had received the dual-exit training, nor were they aware of the requirement for such training in order for Air Canada to operate with the exemption allowing 1 flight attendant for each unit of 50 passengers.
- Although Transport Canada had reviewed and approved Air Canada's aircraft operating manual and the standard operating procedures (SOPs), it had not identified the discrepancy between the Air Canada SOPs and the Airbus flight crew operating manual regarding the requirement to monitor the aircraft's vertical flight path beyond the final approach fix when the flight path angle guidance mode is engaged.
- A discrepancy in the Halifax International Airport Authority's standby generators' control circuitry caused the 2 standby generators to stop producing power.
- Air Canada's emergency response plan for Halifax/Stanfield International Airport indicated that the airline was responsible for the transportation of passengers from an accident site.
- Air Canada's emergency response plan did not identify the airport's Park'N Fly mini-buses as transportation resources.
- The Halifax International Airport Authority's emergency response plan did not identify that the airport Park'N Fly mini-buses could be used to transport the uninjured passengers, nor did it provide instructions on when and how to request and dispatch any transportation resources available at the airport.
- The Air Canada Flight Operations Manual did not identify that the required visual reference should enable the pilot to assess aircraft position and rate of change of position in order to continue the approach to a landing.
- In Canada, the minimum visibility that is authorized by the operations specification for non-precision approaches does not take into account the type of approach lighting system installed on the runway.
- It is likely that, during the emergency, a passenger activated the L1 door gust lock release pushbutton while trying to expedite his or her exit, which allowed the door to move freely.
- The passenger seatbacks were dislodged because the shear pins had sheared, likely as a result of contact with passengers during the impact sequence or emergency egress.
- Recovery of the uninjured passengers from the accident site was delayed owing to a number of factors, including the severe weather conditions; the failure of the airport's 2 standby generators to provide backup power after the loss of utility power; the loss of the airport operations radio network; and the lack of arrangements for the dispatch of transportation vehicles until after emergency response services had advised that all passengers were evacuated and the site was all clear.
- Given that the captain rarely used continuous positive airway pressure therapy, he would have been at risk of experiencing fatigue related to chronic sleep disruption caused by obstructive sleep apnea. However, there was no indication that fatigue played a causal or contributory role in this occurrence.
The TSB reported the captain (ATPL, 11,765 hours total, 5,755 hours on type) was pilot flying, the first officer (ATPL, 11,300 hours total, 6,392 hours on type) was pilot monitoring.
The crew computed in cruise that they needed to correct their altitudes due to the cold temperatures, which required them to cross the final approach fix at 2200 feet MSL (2000 feet MSL according to chart plus the cold temperature offset). The crew expecting a LOC approach to runway 05 further computed the MDA at 813 feet MSL based on the published MDA at 740 feet plus cold temperature offset of 23 feet plus 50 feet correction according to airline standard operating procedures.
The crew was informed that another Air Canada flight had just landed on Halifax's runway 05 following a go around.
The minimum visibility required to conduct the LOC approach was 0.5sm, the 02:00Z METARs reported a visbility of 0.25sm in heavy snow fall. The crew discussed the minimum visibility requirement and established, that they would be able to hold unti 01:00Z before needing to divert to their alternate.
At 02:25z the aircraft entered a hold at 9000 feet MSL, at 02:34z the tower advised the visbility was still 0.25sm.
At 03:16z the tower advised the crew that a SPECI weather report issued at 03:13Z reported a visbility of 0.5sm in heavy snow and 300 feet vertical visibility. The crew determined they could conduct a LOC approach to runway 05.
The crew turned their landing lights off due to the snow and contacted tower to ensure that the approach lights were turned up to maximum intensity (5). Tower, busy with the snow ploughs on runway 05 and another aircraft taxiing, advised the lights were currently on intensity 4 but would be on 5 at the time of landing.
The aircraft descended to 3400 feet MSL with AP1 and autothrust engaged, the aircraft was being configured to flaps 1. 11nm from the threshold flaps were set to 2. The aircraft intercepted the LOC, the crew noticed they could see the ground while looking straight down or at a slight angle down.
8nm from the threshold the gear was lowered, the aircraft levelled off at 2200 feet, 6.7nm before the threshold flaps were set to 3 and full, before reaching the final approach fix the aircraft was fully configured for landing.
2.7nm before the FAF the crew selected Flight Path Angle (FPA) active at 0.0 degrees, the pilot monitoring began to count down the distance to the FAF. At 0.3nm from the FAF the captain selected the FPA to -3.5 degrees.
Tower cleared the flight to land, the runway lights remained at intensity 4 however.
The aircraft crossed the FAF at 2170 feet MSL.
During the descent, due to wind variations, the aircraft descended below the target trajectory. Although the airspeed remained constant, the vertical speed varied between 700 and 800 fpm.
At 03:29:27z the radio altimeter called 400 feet, immediately afterwards the aircraft reached the calculated MDA at 1.2nm before the runway threshold. The first officer called "Minimums, lights only" when the aircraft was 1.0nm from the runway threshold. The captain called "Landing" and began to observe some approach lights. By that time the aircraft had already descended below the published MDA of 740 feet MSL and was 0.3nm farther from the runway threshold than the published distance. The autopilot remained engaged.
At 0.7nm from the runway threshold both crew confirmed they saw some of the approach lights.
At 03:29:47z the landing lights were selected on, followed by a very quick succession of the autopilot being disconnected, an automated call 100, automated call 50 and the pilot monitoring calling to pull up. The aircraft contacted a power line running perpendicular to the runway center line which caused a power outage at the aerodrome. One second prior to impact the captain initiated a go around pushing the thrust levers into the TOGA detent and pulling the side stick fully nose up. One of the left main tyres contacted an approach lights 841 feet before the runway threshold, at 03:30:00z the aircraft's main gear, aft low fuselage and left engine cowling struck the south side of the embankment sloping up to the runway level. The aircraft struck a localizer antenna array striking the ground two more times before sliding along the runway and coming to a stop on the runway 1900 feet down the runway. The aircraft had completely lost electrical power while sliding along the runway.
At 03:30:16z tower activated the crash alarm.
Although no evacuation order had been given, passengers began to open the overwing exits and began to exit the aircraft. The cabin service director instructed the left forward door to be opened and instructed the passengers to exit via the door and slide. The slides at the overwing exits and the cabin door had correctly deployed.
2 minutes after the activation of the crash alarm the first emergency vehicles arrived at the accident site.
All passengers had exited the aircraft within 5 minutes after the aircraft came to a stop, some of them were carrying their carry on luggage. More serious injuries were sat in emergency response vehicles, the other were grouped 200 meters from the aircraft.
About 50 minutes after the aircraft had stopped all occupants were transported to a shelter.
One crew member received a serious, 2 crew and 23 passengers minor injuries, 2 crew and 110 passengers remained uninjured.
The TSB analysed:
The stabilized constant descent angle technique involves flying a constant descent angle so that the aircraft will cross the runway threshold at the correct height. This angle corresponds to the published vertical descent angle (VDA), which defines the flight profile in which the aircraft will cross the runway threshold about 50 feet above ground level (AGL) to ensure landing within the touchdown zone.
One way a pilot can verify the aircraft is on a flight profile consistent with the VDA is to monitor the aircraft’s altitude and distance from the threshold. Since 2014, both NAV CANADA and Jeppesen have included a distance/altitude table on selected charts.
Air Canada’s standard operating procedure and historical practice when flying in flight path angle (FPA) guidance mode was that once the aircraft was past the final approach fix (FAF), the flight crews were not required to monitor the aircraft’s altitude and distance from the threshold or to make any adjustments to the FPA. This practice was not in accordance with Air Canada’s and Airbus’s flight crew operating manuals (FCOM).
Although TC reviewed and approved Air Canada’s AOM and the SOPs, it had not identified the discrepancy between the Air Canada SOPs and the Airbus FCOM regarding the requirement to monitor the aircraft’s vertical flight path beyond the final approach fix when the FPA guidance mode is engaged.
Flight crews select an FPA that corresponds to the published VDA, and the aircraft’s autopilot system maintains the selected FPA. However, in the FPA guidance mode, the aircraft is susceptible to perturbations which, if not compensated for by manual corrections to the FPA, could alter the flight profile. If such perturbations are present during an approach and flight crews are following Air Canada’s practice, flight crews could be unaware of their effect on the selected flight path.
If the actual flight path deviates from the selected flight path as defined by the published VDA, flight crews may have to make adjustments to the flight profile in order to safely continue on with the visual portion of the approach to touchdown. During a stable approach, these adjustments could be minor and may not be sufficient to result in a deviation from stable approach criteria.
The TSB analysed:
During the occurrence flight, as per Air Canada’s practice, once the FPA was selected and the aircraft began to descend, the flight crew did not monitor the altitude and distance from the threshold, nor did they make any adjustments to the FPA. The approach was considered stable and consistent with Air Canada’s training. The flight crew did not notice that the aircraft had drifted below and diverged from the planned VDA flight profile, nor were they aware that the aircraft had crossed the minimum descent altitude further back from the threshold.
Even in clear weather, judging an aircraft’s position relative to the desired vertical flight path can be challenging during a night landing, particularly if there is minimal cultural lighting on the approach path to a runway.
During this occurrence, the visual cues that would have been available to the flight crew included the ODALS, the runway lights, and the precision approach path indicators. The reduced visibility would have diminished the ability of the flight crew to make use of these cues, either by obscuring them or by reducing the time that they were available. The blowing snow likely exacerbated this situation by momentarily or continuously obscuring some or all of the visual cues.
The flight crew recognized that having the approach and runway lights at their brightest selection would make it easier to acquire and maintain the visual cues necessary to conduct a safe landing. The flight crew requested, and the tower controller confirmed, that the runway lights would be on setting 5 for the landing. However, the approach and runway lights were not changed from setting 4 to setting 5; therefore, these lights were not at their maximum brightness setting during the approach.
The reduced visibility, exacerbated by the blowing snow and lack of cultural lighting along the flight path, would have made it difficult for the flight crew to assess the aircraft position and rate of change of position. The flight crew expected to see the approach and runway lights at their maximum brightness. However, the dimmer lights would have created the illusion that the aircraft was further from the threshold than it actually was. This may have led the flight crew to believe that there was more time available to assess the aircraft position in relation to the runway.
When the pilot monitoring called, “Lights only,” the aircraft was about 1.0 nm from the threshold and about 0.35 nm (less than ½ sm) from the only lighted facility on the approach path.
During the approach, the ODALS were on medium setting and the runway lights were on setting 4. The visual cues that may have been available to the flight crew at the MDA can be estimated based on both the ½ sm reported ground visibility and the theoretical visibilities provided by TC.
Based on the reported visibility of ½ sm, the following visual cues may have been available to the flight crew:
- when the aircraft was at the calculated MDA: the lighted facility on the approach path;
- when the aircraft was about 3700 feet from the threshold and the flight crew discussed whether each had acquired the lights: the first 2 ODALS lights; and
- when the aircraft was about 2000 feet from the threshold and the autopilot system was disconnected: all of the ODALS lights and the first 3 pairs of runway edge lights.
Based on the theoretical data provided by TC, the following visual cues may have been available to the flight crew:
- when the aircraft was at the calculated MDA point: the first 3 ODALS lights;
- when the aircraft was about 3700 feet from the threshold and the flight crew discussed whether each had acquired the lights: all of the ODALS lights and about 10 pairs of the runway edge lights; and
- when the aircraft was about 2000 feet from the threshold and the autopilot system was disconnected: all of the ODALS lights and about 19 pairs of the runway edge lights.
With the runway lights and the ODALS on their maximum settings, using the theoretical data provided by TC at the calculated MDA, the flight crew may have been able to see all of the ODALS and at least the first 3 pairs of the runway edge lights.
In the 15 minutes leading up to the accident, the Runway 23 runway visual range (RVR) B values fluctuated above and below the last reported value for ground visibility. Since ground visibility may not be representative of flight visibility, the actual visibility for the flight crew at any point along the approach path cannot be known.
With respect to the decision to continue landing the TSB analysed:
At the MDA, the flight crew were occupied with the need to assess the aircraft’s position and its rate of change of position. The flight crew were relying on the approach and runway lights to achieve this. Using the aircraft’s autopilot system allows more time and resources to assess the overall operational situation.
Considering the challenging conditions to acquire and maintain the visual cues, it is likely that the flight crew delayed disconnecting the autopilot until beyond the minimum descent altitude because of their reliance on the autopilot system.
Flight crews can be subject to a plan continuation bias: without salient triggers, they will continue with their original plan (that is, to carry out the landing). In this occurrence, there was nothing particularly significant to cause the flight crew to re-evaluate their original plan of action. Therefore, the flight crew’s recognition that the aircraft was too low at that point during the approach would have been delayed because of plan continuation bias.
Visibility estimates indicate that a portion of the runway lighting may have been visible to the flight crew on the approach. To detect any change in the aircraft’s position relative to the runway, the flight crew would have used cues such as the aspect ratio between the runway edge lights and threshold lights, the linear perspective of the runway lights, and the amount of space between each runway edge light. However, the cues would have appeared late in the approach and the flight crew would not had much time to interpret and react to them. The uphill slope on the runway may also have aggravated the situation.
Although the flight crew eventually became aware that the runway environment did not look as it should have and began a go-around, they did so too late in the approach sequence to avoid the aircraft colliding with terrain.
The limited number of visual cues and the short time that they were available to the flight crew, combined with potential visual illusions and the reduced brightness of the approach and runway lights, diminished the flight crew’s ability to detect that the aircraft’s approach path was taking it short of the runway.
Although a go-around was initiated, the aircraft stuck terrain approximately 740 feet short of the runway threshold, bounced twice, and then slid along the runway before coming to a rest approximately 1900 feet beyond the runway threshold.
This article is published under license from Avherald.com. © of text by Avherald.com.
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