Unstable Approach Dash 8 Touches Down 450ft Before Threshold
The continuation of an unstable approach following a loss of visual reference led to a Jazz Aviation (dba Air Canada Express) Bombardier DHC-8-102, C-GTAI, contacting the ground short of the runway at the Sault Ste. Marie Airport, Ontario, on 24 February 2015. There were no injuries, but there was significant damage to the aircraft.
While on approach to Runway 30, in conditions of twilight and reduced visibility due to blowing snow, the aircraft touched down approximately 450 feet prior to the runway threshold. Following touchdown, the aircraft struck and damaged a runway approach light before coming to a stop approximately 1500 feet past the threshold.
The TSB say:
An examination of over 500 similar flights on Jazz DHC-8-102s showed that company aircraft routinely fly decelerating approaches below the minimum stabilization height of 500 feet. If approaches that require excessive deceleration below established stabilization heights are routinely flown, then there is a continued risk of an approach or landing accident.
TSB Findings as to Causes and Contributing Factors
- The company standard operating procedures require an approach speed of Vref + 5 knots; however, this is being interpreted by flight crews as a target to which they should decelerate, from 120 knots, once the aircraft is below 500 feet. As a result, the majority of examined approaches, including the occurrence approach, were unstable, due to this deceleration.
- Due to ambiguity in the guidance and uncertainty as to the required speeds during the approach, the crew did not recognize that the approach was unstable, and continued.
- On the approach, the pilot flying reduced power to idle to reduce the approach speed from 122 knots toward 101 knots at 200 feet above ground level. This steepened the aircraft’s vertical path.
- The rapidly decreasing visibility resulted in the airport environment and the precision approach path indicator lights becoming obscured; as a result, the steepened vertical profile went unnoticed and uncorrected.
- Although the loss of visual reference required a go-around, the crew continued the approach to land as a result of plan continuation bias.
- The terrain awareness and warning system did not alert the crew to the aircraft’s proximity to the ground once the aircraft was below 50 feet, possibly due to the rapid rate of closure. This lack of warning contributed to the crew not being aware of the aircraft’s height above ground.
- Due to the uncorrected steepened vertical profile, loss of visual reference, and lack of normal terrain warning, the aircraft contacted the surface approximately 450 feet prior to the runway threshold.
Confirmation bias can predispose pilots to seek cues confirming the belief that any decision to continue an approach is the correct one. In other words, pilots on approach are more likely to seek, and therefore find, information that would lead them to believe that continuing an approach is a safe decision.
In this occurrence, the speeds flown on approach were relatively close to the flight crew’s understanding of what was required for a stabilized approach. This may have led to confirmation bias, in that the crew may not have acknowledged the decelerating speed or loss of visibility, but rather chose to focus on the perception of stability. Their history of successfully continuing approaches once already below the MDA reinforced the notion that the plan to continue was an appropriate option.
Plan continuation bias can be described as a “deep-rooted tendency of individuals to continue their original plan of action even when changing circumstances require a new plan.”
A number of factors can increase the likelihood that a pilot will experience plan continuation bias and continue an approach or landing in unsafe conditions. These include:
- a culmination of tasks;
- questionable weather;
- decreased situational awareness;
- higher workload;
- unstable approaches; and
- confirmation bias.
TSB Findings as to Risk
- If guidance provided to flight crews allows for large tolerance windows, and crews are not trained to recognize an unstable condition, then there is a continued risk that flights that are unstable will be continued to a landing.
- If approaches that require excessive deceleration below established stabilization heights are routinely flown, then there is a continued risk of an approach or landing accident.
- If crews do not report unstable approaches and operators do not conduct flight data monitoring but rely only on safety management system reports to determine the frequency of unstable approaches, there is a risk that these issues will persist and contribute to an accident.
Our comment: The last point illustrates the fallacy of over relying on safety reports!
SMS Shortcomings and Safety Actions
Unstable approaches are one of the key safety issues on the 2016 TSB Watchlist. There is also an outstanding Board recommendation (A14-01) calling for Transport Canada to require commercial air services to monitor and reduce unstable approaches that continue to a landing.
Jazz operates several different aircraft types in its fleet, including de Havilland DHC-8-102s, 300s and 400s, as well as Bombardier CRJ-200s and 705s.
The DHC-8-400s and CRJs are slightly more modern aircraft and are monitored within a flight data monitoring/analysis (FDA) program. The FDA program regularly monitors various parameters of flight and alerts the SQE [Safety Quality Environment] department to events (such as unstable approaches) or trends that might require further investigation.
Currently, the DHC-8-102s and 300s are not monitored within Jazz’s FDA program. When the program began, the future status of these types of aircraft with the operator was uncertain, and, as a result, the investment required to add these types to the FDA program was delayed.
The company did do an initial internal investigation after this accident but:
The corrective or mitigation plan detailed in the report did not include any short- or long‑term action that would address the identified causal factors.
[The company safety department had ] examined the company’s SMS database for similar reports of unstable approaches below 500 feet, but was unable to identify any such events. [That] investigation did not examine recorded flight data from other flights to determine if the unstable approach was a systemic issue or an isolated event.
However, the TSB’s examination of FDR data showed that, by the operator’s definition, more than 84% of the recorded flights were unstable below 500 feet.
…Jazz Aviation LP undertook a number of safety actions such as making amendments to the Jazz DASH 8 Aircraft Operating Manual, by introducing significant changes to the “Stabilized Approach Factors” subsection and adding simulator scenarios to the training syllabus.
An Earlier Accident: G-CUON September 2012
Jazz Aviation DHC-8-301 C-GUON suffered a hard landing and aft fuselage strike at Gaspé Airport, Quebec on 10 September 2012, that suggests attention should have been paid to approach and landing SOPs earlier. In their report the TSB made the following findings as to causes and contributing factors:
- The application of a pronounced nose-up control to reduce the rate of descent resulted in a nose-high attitude. This attitude, combined with a hard landing that compressed the oleos, resulted in the aft part of the fuselage striking the runway, causing significant damage to the aircraft structure.
- The pilot monitoring was focusing attention outside and did not identify the loss of energy in time to notify the pilot flying or to intervene and thereby prevent the hard landing.
- The aircraft crossed the runway threshold with insufficient energy to stop the rate of descent with only an increase in the nose-up attitude at the time of the flare.
- The crew had not received training on the technique recommended by the manufacturer in the event of a higher than normal rate of descent near the ground. As a result, the pilot flying did not limit the nose-up attitude or increase power to reduce the rate of descent, and the aircraft fuselage struck the runway.
They went on to make the following findings as to risk:
- If pilots descend below the optimum approach slope of 3°, there is an increased risk of collision with obstacles during the approach and of landing short of the runway.
- If pilots follow the DH8C SOP precisely when executing a short field landing, the aircraft will pass the threshold of the runway in a low energy state, and be at risk of a hard landing or a hard landing with an aft fuselage strike.
- If pilots adapt the DH8C short field landing SOP to avoid a steep approach in a low energy state by aiming to land close to the threshold while on the usual 3° slope, they are at risk of landing short of the runway.
- If crews do not possess adequate knowledge of the limits of the different visual glideslope indicators, they may continue to follow visual guidance that does not guarantee sufficient clearance above the threshold, increasing the risk of landing short of the runway.
- If pilots do not have direct access to eye-to-wheel height data, they may continue to perform approaches with a visual glideslope indicator that is not appropriate for the type of aircraft flown, increasing the risk of crossing the runway threshold with a reduced safety margin.
- If cockpit voice recordings are not available to an investigation, this may preclude the identification and communication of safety deficiencies to advance transportation safety.
- If stabilized approach criteria do not specify an acceptable speed range, there may be confusion during a critical stage of the flight, increasing the risk of an approach and landing accident.
That TSB report only briefly mentions safety management matters, however the accident was just 5 months after Jazz received an ‘Innovation in Aviation Safety Management Award.’ award:
Jazz’s selection for the award was attributed to our success at integrating several existing systems into one safety and business management system. The judges’ statement on selecting Jazz as the winner was: “The Jazz entry stood out for its evidence of integrating SMS across aviation safety, quality, health and safety, and business. The company demonstrated an excellent reporting culture with high reporting levels and report quality.”
Apart from some limited training and safety promotion actions and focused Ops Manual changes, it is not clear if any deeper learning of wider actions were taken after the 2012 accident.
The Flight Safety Foundation (FSF) has published a Briefing Note on Stabilized Approaches and a study A Practical Guide for Improving Flight Path Monitoring.
IATA Unstable Approaches, Risk Mitigation Policies, Procedures and Best Practices 2nd Edition: This 2nd Edition of this document, collaboratively written by the International Air Transport Association (IATA), the International Federation of Air Line Pilots’ Associations (IFALPA), the International Federation of Air Traffic Controllers’ Associations (IFATCA), the Civil Air Navigation Services Organisation (CANSO), was issued in October 2016.
- Southwest Unstabilised Approach Accident
- Dash 8 Tail Strike: Weakness in Stabilised Approach Procedures involving a heavy landing and tail strike that occurred to Porter Airlines Dash 8 Q400 C-GLQO landing at Sault Ste. Marie Airport on 26 May 2013.
- Dash 8 Runway Excursion after Unstable Crosswind Approach – Danish AIB Report
- Unstable approach led to May 2014 hard landing of Air Canada Rouge A319 flight in Montego Bay, Jamaica
Aerossurance is pleased to sponsor the 2017 European Society of Air Safety Investigators (ESASI) 8th Regional Seminar in Ljubljana, Slovenia on 19 and 20 April 2017. Registration is just €100 per delegate. To register for the seminar please follow this link. ESASI is the European chapter of the International Society of Air Safety Investigators (ISASI).