B732, vicinity Resolute Bay Canada, 2011
From SKYbrary Wiki
|On 20 August 2011, a First Air Boeing 737-200 making an ILS approach to Resolute Bay struck a hill east of the designated landing runway in IMC and was destroyed. An off-track approach was attributed to the aircraft commander’s failure to recognise the effects of his inadvertent interference with the AP ILS capture mode and the subsequent loss of shared situational awareness on the flight deck. The approach was also continued when unstabilised and the Investigation concluded that the poor CRM and SOP compliance demonstrated on the accident flight were representative of a wider problem at the operator.|
|Actual or Potential
|Controlled Flight Into Terrain (CFIT), Fire Smoke and Fumes, Human Factors|
|Type of Flight||Public Transport (Passenger)|
|Take off Commenced||Yes|
|ENR / APR|
|Location - Airport|
|Tag(s)||Approach not stabilised,|
Approach Unstabilised after Gate-GA
Lateral Navigation Error,
Vertical navigation error,
IFR flight plan
|Tag(s)||Post Crash Fire|
Plan Continuation Bias,
Procedural non compliance,
Ineffective Monitoring - PIC as PF,
AP/FD and/or ATHR status awareness
|Safety Net Mitigations|
|Malfunction of Relevant Safety Net||No|
|TAWS||Available but ineffective|
|Damage or injury||Yes|
|Aircraft damage||Hull loss|
|Fatalities||Most or all occupants ()|
|Causal Factor Group(s)|
On 20 August 2011, a Boeing 737-200C (C-GNWN) was being operated by First Air on a domestic passenger charter flight (FAB 6560) from Yellowknife, Northwest Territories, to Resolute Bay, Nunavut. Whilst in the final stages of a daylight Instrument Landing System (ILS) approach at destination in Instrument Meteorological Conditions (IMC), the aircraft struck a hill about 1 mile to the east of the landing runway and was destroyed by the effects of the impact and subsequent post-crash fire. The military TWR controller at the destination airport did not see the aircraft at any time and there was a significant delay before the wreckage was located. Twelve of the 15 occupants were killed and the remaining 3 sustained serious injuries.
An Investigation was carried out by the Canadian TSB. The Flight Data Recorder (FDR) and 30 minute Cockpit Voice Recorder (CVR) were both recovered and, despite an intermittent fault with the former, relevant recordings from both were successfully downloaded. However, the FDR recorded only 24 parameters and these did not include position or time, so an available military radar recording (which had not been available to Resolute Bay ATC at the time of the accident) plus surveyed ground impact markings were used to re-create the aircraft track. The FDR data on altitude, indicated airspeed and heading was then used to create a flight path which was linearly interpolated to the track to create a smoothed and accurate replication of the flight path.
It was noted that no ELT signal had been picked up after the crash and this was found to have been the result of the inappropriate installation of the equipment on the aircraft. It was also found that the identifier in the ELT was not valid, having remained unchanged from when the equipment was installed in a previous aircraft.
It was also found that two ADs had not been complied with in respect of the accident aircraft and that, as a result, its C of A had been invalid. However, it was concluded that this had had no direct bearing on the accident and no evidence of any other relevant maintenance issues was found.
It was established that the aircraft commander had previously been a 737 First Officer at the operator and had been promoted to Captain a little over three years prior to the accident. The First Officer had joined the company four years earlier on the ATR42, achieving a command on that type before being transferred to the 737 fleet as a First Officer two months prior to the crash and accumulating just 100 hours on type. Both were familiar with Arctic operations. The Investigation found no evidence to indicate that fatigue of either pilot had been a contributing factor to the accident.
The final weather report for Resolute Bay given to the crew just over half an hour prior to the accident gave the wind velocity as 180° at 8 knots, visibility 10 sm in light drizzle, overcast cloud at 700 feet agl with temperature 6.3°C and dew point 6°C. A SPECI issued 7 minutes after the impact gave the visibility as 5km and overcast cloud at 300 feet agl.
The approach briefing given by the PF prior to commencing descent had included his intent to use the Area Navigation Systems (GPS-based) system to turn onto the Instrument Landing System (ILS) LOC before switching to the ILS but had not unambiguously communicated how this was intended when there was more than one possibility. The Investigation considered that as such the briefing had been “non-standard and incomplete” when one of the main purposes of it should have been to ensure that both pilots had the same expectations and thus a common basis for shared situational awareness.
It was found that the descent from cruise altitude had been commenced late and had maintained a direct track to the intended turn onto final approach. The rate of descent and airspeed were both high. FDR data showed that the aircraft passed 10000 feet altitude at 310 KIAS, well above prevailing 250 KIAS speed limit. Although it was considered that compass setting and cross setting procedures applicable to high latitude operations had been correctly followed, it was found that a considerable compass error had been present and had increased by the time the aircraft reached final approach.
The turn onto the ILS LOC from the south west at an intercept angle of 51° was commenced with the aircraft about 600 feet above the nominal vertical profile with the AP engaged and VOR/LOC selected on the FD at 184 KIAS. The aircraft therefore flew through the LOC before beginning the turn left towards the centreline with an intercept angle consistent with the ‘fly left’ indication displayed on the HSI LOC beam bar. However at about this time, with the AP about to complete alignment on the LOC at a range of about 8 miles, it was concluded from examination of the FDR data and consideration if the aircraft FD/AP system that the PF had made sufficient Control Wheel Steering (CWS) input to inadvertently disconnect the VOR/LOC mode. This would have resulted in the AP reverting to MAN and HDG HOLD so that with the aircraft bank angle at that point less than 5°, the AP had established and maintained wings level and begun to track the selected heading which was set to the FAT. The resulting effect of this on the FD command on the ADIs would have been to change (presumably unnoticed) from a left turn to ‘fly ahead’ based on the wings level tracking of the selected heading. With a 3° crosswind component, the aircraft had thereafter begun to slowly but progressively deviate to further to the right of the LOC so that both HSIs would have soon shown continued movement of the HSI LOC course deviation bar to the left until it reached, and thereafter remained at, full scale deflection. The resultant steady track to the point of impact east of the runway with the AP remaining engaged is shown on the diagram below reproduced from the Official Report.
The Investigation considered why the AP status change was apparently never noticed by either pilot but came to no conclusion. As to why no corrective action was taken to keep the aircraft on the ILS LOC, the CVR recording provided clear evidence that although the First Officer had recognised the deviation and pointed out that it corresponded to the position indicated by the GPS, the PF had failed to take any notice of these observations despite having no external visual reference. With the expected intercept angle remaining on the HIS in the presence of a significant but unappreciated compass error, the PF appeared to have an expectation that the required track would be regained. Overall, it was considered that the conversation between the two pilots during this final descent had been wholly ineffective. It was also noted that the late configuration of the aircraft and resultant failure to stabilise the aircraft or go around in accordance with SOPs was probably at least partially a result of the high speed arrival and the developing confusion on the flight deck as a shared situational awareness was lost.
The descent on the ILS vertical profile was continued until the automated ‘minimums’ call generated by the GPWS/TAWS occurred. This finally triggered a go around decision by the PF but, just as this action was commenced, terrain impact had occurred. The Investigation noted that had a GPWS/TAWS been fitted rather than the GPWS, it was likely that a more timely useful warning of terrain proximity was likely to have been generated.
The formal statement in respect of Causes and Contributing Factors (which did not distinguish between the two) was as follows:
- The late initiation and subsequent management of the descent resulted in the aircraft turning onto final approach 600 feet above the glideslope, increasing the crew's workload and reducing their capacity to assess and resolve the navigational issues during the remainder of the approach.
- When the heading reference from the compass systems was set during initial descent, there was an error of −8°. For undetermined reasons, further compass drift during the arrival and approach resulted in compass errors of at least −17° on final approach.
- As the aircraft rolled out of the turn onto final approach to the right of the localizer, the Captain likely made a control wheel roll input that caused the autopilot to revert from VOR/LOC capture to MAN and HDG HOLD mode. The mode change was not detected by the crew.
- On rolling out of the turn, the Captain's horizontal situation indicator displayed a heading of 330°, providing a perceived initial intercept angle of 17° to the inbound localizer track of 347°. However, due to the compass error, the aircraft's true heading was 346°. With 3° of wind drift to the right, the aircraft diverged further right of the localizer.
- The crew's workload increased as they attempted to understand and resolve the ambiguity of the track divergence, which was incongruent with the perceived intercept angle and expected results.
- Undetected by the pilots, the [ADI] flight directors likely reverted [from] AUTO APP intercept mode as the aircraft passed through 2.5° right of the localizer, [to] providing roll guidance to the selected heading (wings-level command) rather than to the localizer (left-turn command).
- A divergence in mental models degraded the crew's ability to resolve the navigational issues. The wings-level command on the flight director likely assured the Captain that the intercept angle was sufficient to return the aircraft to the selected course; however, the First Officer likely put more weight on the positional information of the track bar and GPS.
- The crew's attention was devoted to solving the navigational problem, which delayed the configuration of the aircraft for landing. This problem solving was an additional task, not normally associated with this critical phase of flight, which escalated the workload.
- The First Officer indicated to the captain that they had full localizer deflection. In the absence of standard phraseology applicable to his current situation, he had to improvise the go-around suggestion. Although full deflection is an undesired aircraft state requiring a go-around, the Captain continued the approach.
- The crew did not maintain a shared situational awareness. As the approach continued, the pilots did not effectively communicate their respective perception, understanding, and future projection of the aircraft state.
- Although the company had a policy that required an immediate go-around in the event that an approach was unstable below 1000 feet above field elevation, no go-around was initiated. This policy had not been operationalized with any procedural guidance in the standard operating procedures.
- The Captain did not interpret the First Officer's statement of “3 miles and not configged” as guidance to initiate a go-around. The Captain continued the approach and called for additional steps to configure the aircraft.
- The First Officer was task-saturated, and he thus had less time and cognitive capacity to develop and execute a communication strategy that would result in the captain changing his course of action.
- Due to attentional narrowing and task saturation, the Captain likely did not have a high-level overview of the situation. This lack of overview compromised his ability to identify and manage risk.
- The crew initiated a go-around after the ground proximity warning system “sink rate” alert occurred, but there was insufficient altitude and time to execute the manoeuvre and avoid collision with terrain.
- The First Officer made many attempts to communicate his concerns and suggest a go-around. Outside of the two-communication rule, there was no guidance provided to address a situation in which the pilot flying is responsive but is not changing an unsafe course of action. In the absence of clear policies or procedures allowing a First Officer to escalate from an advisory role to taking control, this First Officer likely felt inhibited from doing so.
- The crew's crew resource management was ineffective. First Air's initial and recurrent crew resource management training did not provide the crew with sufficient practical strategies to assist with decision making and problem solving, communication, and workload management.
- Standard operating procedure adaptations on FAB6560 resulted in ineffective crew communication, escalated workload leading to task saturation, and breakdown in shared situational awareness. First Air's supervisory activities did not detect the standard operating procedure adaptations within the Yellowknife B737 crew base.
Comprehensive Safety Action in the light of findings made during the Investigation and communicated to both First Air and Transport Canada was noted. As a result, only one Safety Recommendation was made as follows:
- that Transport Canada require CARs Subpart 705 operators to monitor and reduce the incidence of unstable approaches that continue to a landing. [A14-01]
However, the Board also recorded an outstanding ‘Safety Concern’ to the effect that “without a comprehensive and integrated approach to CRM by Transport Canada and aviation operators, flight crews may not routinely practice effective CRM”.
Release of the Final Report was authorised on 5 March 2014 and it was officially released on 25 March 2014.
- Controlled Flight Into Terrain (CFIT)
- Approach and Landing Risks
- CFIT Precursors and Defences
- Situational Awareness
- Cross-checking Process
- Crew Resource Management
- CRM Skills Training (OGHFA BN)
- Monitoring Skills (OGHFA BN)
- Terrain Avoidance and Warning System (TAWS)
- Terrain Awareness
- Post Crash Fires
- "Monitoring Matters" - Guidance on the Development of Pilot Monitoring Skills: UK CAA Paper 2013/02