Nothing to Reinvent

Correcting deviations as early as possible during instrument approach procedures — within a comprehensive strategy that helps flight crews to consistently accomplish stabilized approaches in large commercial jets — offers significant potential to avert predominant types of air transport accidents, according to results of French research begun in 2011.

André Vernay, human risks program manager, Direction Générale de l’Aviation Civile (DGAC) of France, in November explained threat concepts and solutions derived from the DGAC’s ongoing analysis of noncompliant approaches (or NCAs), during Flight Safety Foundation’s 67th annual International Air Safety Summit in Abu Dhabi, United Arab Emirates.

A DGAC-appointed research team inside the directorate’s Safety Management Coordination Office coined this term as a research construct during preliminary reviews of 13 accidents and major incidents — drawn from a 35-year period — after common causal factors sparked concerns. The events were assessed against the flight rules, regulatory policy statements and requirements that all of France’s airline pilots study during training.

Vernay said that the approaches analyzed during the research represented an identified risk that required joint safety actions. “An NCA can lead to loss of control–in flight, controlled flight into terrain, runway excursions or non-stabilized approaches, for example,” he said. “We had cases of aircraft stabilized at 200 ft — it’s not acceptable. The crews had to go around per standard operating procedure [SOP], but then the decision was made to ‘fight.’ A compliant approach is to land safely; that’s all it is.”

He explained the team’s definition of noncompliant approach using a diagram of the period in a typical instrument approach (Figure 1) that begins at the last segment preceding the aircraft’s turn onto the final approach course and continues to a designated point, defined by the operator’s SOPs and stabilized-approach criteria, by which the flight crew must decide explicitly if the approach is stabilized or non-stabilized.

The team’s model depicts a compliant approach as a green safe sector, and states that any of the following deviations creates a noncompliant approach: an interception angle to the final approach course greater than 45 degrees (or 30 degrees if parallel active approaches are being conducted); an intermediate leg providing less than 30 seconds for the flight crew to prepare the aircraft for landing (or less than a 2.0-nm [3.7-km] distance on a global navigation satellite system–based, nonprecision approach) before descent from the final approach course interception altitude at the final approach point; a glideslope interception from above; or operating with a non-adapted speed on final (i.e., greater than 180 kt at the final approach point).

Among influences on this model were six safety-reference documents currently used in the national aviation system. “An approach is a shared maneuver between airport facilities, controllers, crews, designers and manufacturers,” Vernay said. “Everything is written. There’s nothing new, nothing to rebuild, nothing to reinvent, so the compliant approach is something costless and already safely built.”

Since 2009, the risk portfolio of the French state safety program has emphasized these risks, which also are a part of the European Action Plan for the Prevention of Runway Excursions published by Eurocontrol, a team partner. Section 4 of the IATA Safety Report 2013 by the International Air Transport Association also provided relevant data and analysis derived from fatal approach accidents involving flight crews’ lateral, vertical and speed deviations. Operators’ deficiencies in safety management were cited by IATA as a factor when inadequate SOPs for the flight crew also were identified by accident investigations. Crew noncompliance with SOPs also was considered (see “EGPWS Data Show Benefits of Multiple Technologies for Premature-Descent Alerts”).

Relevant decision-making interactions between other stakeholders and flight crews conducting an approach and landing were studied during the team’s analysis using a tool designed and developed by Vernay called the decision and action wheel (DAW). “There is not only one decision-making process, there are three in the approach,” Vernay said, adding that the expectation of the authorities is clear: “If you’re outside of the procedure, you will go around.”

He labeled the decision-making processes as the expected process involving factors fixed and documented by the authority that become part of the pilot’s knowledge base; the required process involving factors influenced by the procedures and trajectory developed by an organization to, for example, remain clear of obstacles in the environment; and the personal process involving decisions using the individual pilot’s risk criteria and based on experience, the emotion of the pilot and/or responses to conditions being encountered.

“The operator will fix in the SOP the elements or the point where they want the crew to abort, to renounce a continued approach, and to proceed on a go-around,” he said. As a pilot, personal decision making is “linked to my experience in the aircraft, to my knowledge, to my confidence, to my fatigue, to my vigilance,” he added.

Vernay applied the DAW to identify points in time during the sequences of actual accidents at which the flight crew’s behavior differed from what would be expected, for example, by the instrument procedure’s designer, or from conformity to the airline’s SOPs, or from how typical pilots would conduct the approach in the same situation. “So the criteria that we found in the regulations and the approach procedures can be strong signals prior to conducting the non-stabilized approach or reaching the stabilization point,” he said. “If nothing is in place to be checked on final, and the final goal is to pass the stabilization door [i.e., gate], then threats to safety can happen before the stabilization point.”

He cited as an example one of the 13 events studied by the team, the fatal crash on Feb. 25, 2009, of Turkish Airlines Flight TK1951, a Boeing 737-800, during its approach to Runway 18R at Amsterdam Schiphol Airport (ASW, 6/10). Vernay’s plan-view diagram of the accident approach sequence showed deviation from the published procedure for joining the final approach course, requiring the flight crew to intercept the glideslope from a point far above the designed interception altitude. His profile-view diagram showed the point at which the operator’s SOP required the flight crew to check their adherence to stabilized approach criteria and where the accident crew struggled to recover the stabilization elements before that point.

“They didn’t manage that. They didn’t succeed,” he said. “But I can tell you that when we worked on the investigation reports, we understood that from the beginning of the descent until the crash, the crew was more than busy trying to come back to the elements. According to the investigation report, no pilot fully monitored the flight path and aircraft speed.”

To put the accident flight crew’s decisions and actions into the broader context of noncompliant approaches, however, Vernay cited one investigation board finding in the Schiphol accident that, before this crash, 50 percent of approaches to Schiphol Runway 18R had involved turns onto the final approach course beyond the turning point that readily enables flight crews to conduct a stabilized approach. “So it wasn’t a single case. It was a habit. It was something that was accepted by everybody. Nobody complained. Nobody said anything to the controllers during months and months. No feedback had ever mentioned that this operational mode led to a higher risk,” he said, based on the Dutch report’s analysis.

Insights such as these led the DGAC to collaborate on a further phase of analysis of noncompliant approaches with air traffic control (ATC) and operators at many French airports. For example, at Paris–Charles de Gaulle (CDG) Airport, a new software plug-in to the automated separation minima infringement–
detection tool devised by controllers generated a daily record of approaches that fit the noncompliant approach criteria.

“Over two years now, the record there has shown 4,000 noncompliant approaches a month and dozens of cases of glideslope interception from above,” Vernay said. The research team recognized that the controllers at participating airports face inherent difficulties in simultaneously balancing at least four objectives: maximizing traffic capacity by efficient use of airspace; mitigating noncompliant approaches; preventing overshoots during localizer course arrivals to parallel runways; and preventing infringements of the minimum separation standards of 3 nm and 1,000 ft.

During these discussions, the DGAC team also asked participating controllers, “What is the gain if you keep an aircraft at 180 kt until 5.0 nm [9.3 km] instead of asking for 160 kt at 6.0 nm [11.1 km] or 150 kt at 5.0 nm [9.3 km], for example? Anything?” Vernay recalled. “They didn’t have an answer because they didn’t have to look at the gain or the loss of time. It’s something like 25 seconds — 25 seconds to risk a non-stabilized approach.”

However, when controllers reviewed their data and realized the level of risk created by vectoring aircraft using noncompliant interception angles, they responded, “We must do better.” They then took responsibility for a solution, Vernay said. At CDG, for example, they digitally overlaid chevron-shaped interception marks on ATC displays (Figure 2) to help controllers guide any aircraft according to the standard-trajectory procedure.

Another solution involving ATC and operator collaboration stemmed from one meeting in which DGAC listened as operators discussed unaddressed problems. “We were surprised that some operators with advanced aircraft said, ‘If I’m closer to the runway threshold than 8 nm [15 km] at 180 kt, I have big problems,’” he said. A current DGAC safety bulletin — containing information confirmed by manufacturers such as Airbus — advises controllers that no ATC instruction requiring airspeed of 180 kt or greater should be issued while the aircraft is less than 8 nm from the runway threshold.

New areas of the DGAC’s research include mitigating the influence of tail winds on noncompliant approaches, enhancing pilot reports of tail wind–risk factors during arrival, determining which subcategories of noncompliant approaches represent the highest risk, and addressing discrepancies in aviation safety professionals’ interpretations of the ATC phrase wind calm.