AIR|Aligner Insight
Improving Pilot Understanding of Loss of Control In-Flight Conditions
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Context and Situation
Loss of control inflight (LOC-I) accidents led to more than 60% of aircraft accident fatalities from 2006 to 2018 (2,462 of 4,075 deaths). But while they are the leading cause of aircraft fatalities, they are also among the most preventable. As the International Air Transport Association reports, “LOC-I accidents often result from failure to prevent or recover from a stall and/or an upset. Pilots should not only be able to avoid stall and/or upset but should also be able to recover from such situations should they occur.”
While numerous factors and factor combinations contribute, the overarching source of LOC-I is an inability to recognize, accurately interpret, and respond to a changed condition of the aircraft. According to IATA, “LOC-I accidents do not occur because of an inability to fly the aircraft manually, but rather due to a late or non-decision to take over control manually.” Research also shows that the flight crew’s loss of situational awareness (often abetted by automation) is the principal cause of failure to recover in time and effectively.
With these circumstances in mind, the question is how pilot awareness can be heightened and responsiveness attuned so that LOC-I incidents are better controlled and more survivable when they do occur.
This article details a technology solution that can help pilots prevent and recover from upset and stall conditions by providing a more holistic picture of flight and by supporting accurate interpretation of and response to impending upset or stall conditions.
Preventive and responsive measures
Current research across a range of sources recommends specific preventive and response measures in response to LOC-I incidents:
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Preventive measures. Preventing loss of control in-flight depends on increased attention to “precursors” of loss of control: flight controls and displays, awareness of conflicting information, the application of interpretive insight across a range of these inputs. This entails what IATA refers to as helping develop a “predictive cognitive picture” of what the aircraft should be doing – often in contrast to what the instruments might be showing.
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Responsive actions. Highly-skilled pilots respond to potential LOC incidents by “relying on holistic monitoring of all information available.” These measures include, for example, comparing attitude, altitude, heading, and airspeed information to see if – together – conflicting information makes sense against a broader interpretation. For example, “…presented with conflicting airspeed information, [skilled pilots] will reference the aircraft attitude and power settings to see which airspeed makes more sense…even if there is no redundant sensor for each piece of information.”
There is no substitute for the judgment and skills of an effective pilot, but information or displays that support a more holistic interpretation of what can otherwise be a dangerous and unpredictable situation in-flight can have significant value.
How AIR|Aligner helps
Airspeed Systems has patented a solution that combines airspeed and angle of attack (AOA) data in a “matched array” that displays a given range of aligned instrument values in a single instrument. Potentially anomalous instrument readings can be checked against expected alignment of these parameters, so when sensor or instrument failure drives the received combination out of alignment with the expected range of values, AIR|Aligner can warn the pilot, or it can be an independent support for more accurate estimation of airspeed, AOA, or attitude.
The exhibit below illustrates how the system works. First, for any given aircraft, the combination of AOA and airspeed that represents relevant values in the flight envelope are pre-programmed and transformed into a linear representation of their matched values (see 1). During flight, flight data is captured on an ongoing basis, (2), an indicator shows whether the combination of airspeed and AOA are aligned: accurate alignment is represented as the diagonal positioned on the diagonal, (3). By contrast, when AOA and airspeed are out of alignment – for example in a potential stall or upset condition, the indicator will more than likely be off the diagonal. The pilot uses this information to exert greater control over the flight directly, or as an additional perspective compared with other available information.
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The AIR|Aligner display is designed to be called up on the aircraft’s existing primary or secondary flight display and used as an additional reference for pilots to use in interpreting the aircraft’s flight mode. Further, because these two critical measures are combined in a single instrument, they have the potential to provide faster indication of an out of balance flight mode – circumstances in which every second counts. Despite these benefits, however, the combined display should not be considered sufficient alone, but additive to the existing information a skilled pilot can refer to in any of multiple use cases, including:
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When conditions mask external references. Air France’s Airbus A330 Flight 447 from Rio de Janeiro to Paris crashed in pitch back flight conditions when its air data probes became iced over mid-flight at night over the Atlantic, causing the autopilot to disconnect. Absent any external references against which to check the aircraft’s attitude and AOA, the crew stalled the aircraft and crashed, killing all on board. Even incorrect data when combined in a single display might provide perspective that helps interpret flight mode even absent visual references.
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When instruments display conflicting information. In many instrument-related LOC-I’s, conflicting or incorrect cockpit information is to blame, even when conditions support external visual references. For example, Brigenair Flight 310, a Boeing 757, crashed shortly after takeoff on a flight from the Dominican Republic to Germany, because of a pitot tube became blocked by an insect nest. The inability to verify either AOA or airspeed or both might have been offset to a degree by an instrument able to display both together. An faulty indication – even driven by bad information – showing the two were out of alignment might have pushed the pilots to seek additional information to accurately estimate aircraft speed.
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When upset or stall conditions are encountered. Finally, when an aircraft’s flight mode suggests a stall or other upset is in process – the AIR|Aligner combined display can provide a useful reference to the alignment of these two metrics. Apart from built-in alerts, the position of the central indicator above or below the reference center diagonal, combined with how far off the diagonal the indicator may be can provide that margin of insight that helps a pilot better interpret the situation and eventually recover. Note that even the multiple redundancies in modern digital systems are not entirely insulating; in 2008, an XL German Airways Flight 888T Airbus 320 was unable to recover when two frozen AOA sensors outvoted the good sensor, stalling the aircraft.
But the value of matched array AOA and airspeed information does not depend on unfailingly accurate instrument readings, but on a comparison of key data that provides additional insight that pilots will then add to other available information to assess what is really happening to the aircraft (for example, attitude comparisons and GPS-based cross-checks).
Today, work is ongoing to develop technologies that anticipate flight mode challenges and provide interactive pilot support information, including enhanced synoptic pages (eSyn) including System Interaction Synoptics (SIS), and simplified electronic checklists (sECL). All of these seek to combine, unify, and rapidly display in the cockpit complex situational information and the status of subsystems.
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Sophisticated advances should continue because the stakes are so high. But AOA and airspeed are the most fundamental indicators, often emerging as the greatest sources of risk, both when data are bad and when the aircraft’s flight mode is compromised. Quickly comparing these metrics can provide low-cost, easily installed, and valuable information when seconds count.