Situational awareness on the flight deck

Aircraft Engineering and Aerospace Technology

ISSN: 0002-2667

Article publication date: 1 August 2000




(2000), "Situational awareness on the flight deck", Aircraft Engineering and Aerospace Technology, Vol. 72 No. 4.



Emerald Group Publishing Limited

Copyright © 2000, MCB UP Limited

Situational awareness on the flight deck

Situational awareness on the flight deck

Keywords: Conferences, Royal Aeronautical Society, Flight safety

At the Royal Aeronautical Society this Conference explored the current and future contributions by systems and equipment and detailed insights into the maintenance of situational awareness, the problems that can arise and possible solutions, both now and in the future. Speakers from Boeing concentrated on the vertical situation display (VSD) being developed and remarked that inaccurate or lack of vertical situation awareness has been shown to be a major contributor in many commercial air transport accidents and incidents. Lack of vertical situation awareness also contributes to certain inabilities.

This paper covers an example of how vertical situation awareness is being addressed and enhanced. It was thought essential to have possible solutions that could be readily retro-fit as well as forward fit into the fleet. Various key formats were studied with all assuming the existence of a terrain warning system (TAWS). These valuations were summarised with appropriate rating scales and for the current safety targets, VSD represented one of the more effective and practical interventions, i.e. a side-looking vertical profile display.

It was decided to focus on a 2-D side-looking profile VSD due to both the advantages and the ease of implementation. The track type of VSD, i.e. one in which the display depicts a swath that follows the current track of the aircraft (referred to as the track type of VSD) is further investigated. One of the specific issues identified with the track type was that the flight crew really wanted additional look ahead in the direction of a turn. The path type of VSD gives this automatically, at the sacrifice of seeing what is actually in the aircraft's current track. In order to account for the flight crew's desire, an algorithm was implemented that opens up the slice or swath in the direction of the turn. This is sufficient to give the flight crew the look ahead into the turn that they appear to require on the VSD. For simplicity, it was decided to depict the swath on the lateral display by means of two dotted or dashed lines. A design solution also adopted was a hybrid one, in which both the aircraft symbol and the altitude scale move.

Together with VSD, various interventions were evaluated, including enhanced ground proximity warning system (EGPWS), area navigation (RNAV) constant angle approaches, controlled flight into terrain (CFIT) training aid, and flight path guidance presented on HUD. From Table I it can be seen that the highest amount of potential accident prevention is accrued by the VSD compared to the other four. The combined effect of VSD together with other systems is also greater than the other systems combined together.

Table I Comparison of accident reduction rates among five different interventions

A system approach to situational awareness was provided by Rockwell Collins in which it was noted that the flight deck view of the external environment (traffic, terrain and weather) must be consistent with the air traffic control view to support delegation of responsibility and safe transfer of control. Situational awareness provides an essential contribution to both air and ground capabilities. The functions available to help meet the requirement for safe, efficient and reliable operations include: communications; navigation systems; airspace operational data; weather and atmospheric data; relevant traffic dependencies; and terrain and obstacle data. The question ultimately is how are these data to be presented to support flight deck decision making? On the glass flight deck design, raw data have been partially replaced by processed data and displayed on a common display. The integration of additional information associated with evolving airspace changes that attempt to address the maintenance of flight crew situation awareness is also to be considered.

Several challenges exist: how do we mitigate information overload; what information is required, and what information should be classed as secondary and accessed only on a request basis? It is also necessary to view what information in its raw forms should be available, as opposed to offering a family of derived answers. The concepts of collaborative decision making and delegated responsibility are required to move forward and it is necessary to ensure that avionics and ground automation are developed to a common concept.

Airbus flight decks

The history of situational awareness on Airbus flight decks was described with respect to its introduction. Considerable progress has been made in recent years in knowing where you are relative to a given ground feature, knowing how you are situated vertically, and being aware of your energy situation. The glass cockpit of the A320 followed by other Airbus aircraft has been responsible for this. The main improvement in situational awareness is in the PFD and the ND.

Now, everything you needed to know about your position relative to the flight plan, the waypoints, or the airport is presented on the ND. The situation relative to the terrain is solved with the EGPWS recently certified and installed on all the FBW family. A background display of the terrain ahead of the aircraft is shown on the ND, available in either ARC or or Rose Nav modes. Colour is used to highlight the dangerous terrain. A visual and aural caution is given if the aircraft is approaching high ground, the latter repeated every seven seconds. A new development is the "peaks" display which will also be integrated into the ND, and allowing a view of the terrain beneath when at cruising altitude.

There are some aids to vertical situation awareness implemented but we believe that the vertical cut should be displayed quantitatively. Airbus have chosen to develop a "vertical cut" display, which, however, requires larger displays so cannot be incorporated immediately but is being developed for the A3XX. This display is geometrically correct in that the heights above the terrain are corrected for temperature. The information is also presented by reference to both aircraft barometric altitude and radio height, when it is available. Commonality has been retained where possible and new technology embodied.

Awareness of energy is another element of situational awareness that has been taken into account in Airbus flight deck design, with new features having been added. A few years ago, the aural callout "speed, speed, speed" was introduced; also reactive windshear, with more recently, predictive windshear. A visual representation is available on the ND of the aircraft situation relative to other aircraft which might be a threat. In the future is long-term station keeping using the position, speed and direction of each aircraft. During ground operations, a camera to be introduced on the A340-600 will tell the situation of the aircraft relative to the runway. Later, an aid for navigating on the ground will be added. Other developments are also being pursued.

Free flight and safety improvements

Smiths Industries Aerospace detailed a free flight scenario which will introduce more information on to the flight deck. Free flight aircraft must provide less of a burden to ATC. An aircraft equipped with automatic separation assurance system would be allowed a higher degree of direct routeing. The adoption of free flight has three categories: technical; operational; and legal.

The technical issues include traffic, a major source of data which will be ADS-B, covering air-to-air and air-to-ground communication of flight plan intent information. Also weather is an issue, as well as terrain. Databases are now available that cover continental Europe in some detail. Airspace information is vital; with the aircraft staying within a boundary or "safe bubble" meteorological features are also important, containing every problem possible from an awareness point of view.

The adoption of a free flight operational scenario will require co-operation between the three major players; the ground system, the airborne system, and the airlines. An autonomous aircraft scenario offers the greatest level of failsafe operation, in which each aircraft is required independently to take action to avoid all other aircraft. An ASAS (airborne separation assurance system) equipped aircraft must calculate its own manoeuvres to avoid its detected conflicts. Defined priority is essential, which can be done in a number of ways: fixed priority rules; priority rules based on phase of flight; random assessment; and negotiated priority automatic/manual.

As far as legal issues are concerned, free flight could see additional technology added to the FMS, which could upgrade the FMS to a flight critical system. This could lead to the question, who is flying the aircraft, the airline that installed the system; the pilot; or the authority that certified it for the company that wrote the algorithm.

The most likely operational scenario will involve both the ground and air in a co-operative solution. Aircraft under ATC control should be vectored by ATC to avoid conflicts with ASAS aircraft, thereby giving these aircraft a higher priority. Smiths Industries is actively involved in free flight as a partner on projects which are researching new techniqes.

Flight safety improvements through advanced avionics solutions were detailed by Honeywell, which paper concentrated on three systems that have been developed to address CFIT, loss of control, and mid-air collision. These are airborne weather radar, GPWS, and traffic alert and collision avoidance system (TCAS) or airborne collision avoidance system (ACAS).

Weather radar was introduced in the 1940s and has advanced considerably over the years. This now includes a display of the vertical profile of the precipitation echoes in addition to the plan view. The radar became a combined situational awareness aid with the advent of predictive windshear detection.

GPWS, introduced in 1967, was originally based on information from the radio altimeter, combined with barometric altitude, vertical speed and aircraft configuration logic. Improvements followed over the years and a significant reduction in CFIT accidents. LETR systems transformed the GPWS to a situation awareness aid.

In 1986 the first generation TCAS was produced and improvements have been made since then. It has become apparent that these systems need to communicate with each other, as in some situations it is possible to get suimultaneous (and possibly conflicting) alerts from the radar, GPWS and TCAS. Prioritization of alerts became necessary and benefits available include radar antenna autotilt; enhanced turbulence detection; and improved TCAS/ACAS alerting.

Fatigue and situational awareness

From the Universite¨ Rene¨ Descartes, Paris, came a paper on approaches towards maintaining situational awareness; the contribution of a fatigue countermeasures interface. It reviewed the specification and evaluation of a support system aimed at monitoring the vigilance and alertness of aircrews subject to sleep pressure. Visual and audio alert warnings timely inform the pilot of any reductions in vigilance hence induced planned naps to alleviate sleep pressure.

The electronic pilot activity and alertness monitor (EPAM) is based on both main task performance measurements and the evaluation of operator status by means of physiological indications, since such an arrangement contributes to a better detection of pilot reactivation needs. The activity part includes two modes. The first, EPAM, monitors pilots' interactions within the flight deck. The second is based on video recording of pilots' eyes during flight.

Currently, the device is in an operational evaluation stage with long range flights (Brussel-New York-Brussels) undertaken on Airbus A340 aircraft. The results depicted in Figure 1 show that five potential alerts occurred before rest. The data concerning video recordings are currently being processed to improve the algorithm that will be tasked to compute various ocular parameters. At the same time, an investigation was conducted on the effect of the operational procedure that pilots should adopt after the release of an auditory alert. A first version of this reactivation procedure was designed to increase a pilot's situational awareness after a decreasing alertness period. It is composed of a string of operationally meaningful tasks with numerous flight instruments and systems monitoring items related to situational awareness to be performed as if the pilot had been some time absent from the flight deck.

Figure 1 Hypnogram during in-flight nap (a) and alpha/delta ratio (c). EPAM warnings for ten, 15, 20 and 25 minutes, without interactions with cockpit systems (b)

The initial results confirm the feasibility of the EPAM concept. They also show that the reduction of pilots' interactions with cockpit interfaces is often related to decreased alertness detected by physiological means. Results also do suggest that the sole measurement of these interactions is not sufficient to predict alertnesss decrements and that these could be intercepted by individual methods such as those stemming from eye movements. The data confirm the efficiency of in-flight napping strategies on the specific roster selected for these flights as it induced a high level of monotony and fatigue. In adopting this strategy, however, pilots preferably have to be supported by a device such as EPAM. Moreover, to this day, no flight deck means do exist to enable detecting simultaneous sleep onsets for both pilots.

Current solutions and has EFIS delivered?

A contribution from Thomson CSF-Sextant mentioned four avionics elements that contribute to improving the CFIT situation but are not widely utilized as an integrated solution. These are heads up flight display system (HFDS), advanced flight management system (FMS), ground collision avoidance system (GCAS), and terrain awareness and warning system (TAWS). These are evolving and being constantly refined.

The several elements referred to can and do contribute to a reduction in CFIT. These solutions are evolved products with origins in military aviation, whether in concept or actual product. The Sextant HFDS couples the external environment with an awareness of the aircraft state, within bounded parameters, which helps the flight deck to determine a safe flight path under less than optimum visibility. There is no visual transition from "head down" instruments to "head up" visual required with HFDS. Response times are enhanced, take-off conditions are improved, and, in the case of autopilot failure and subsequent go-around, the HFDS provides enhanced safety. There are basically three types of HUDs: the stand alone; the autoland monitor HUD; and the hybrid HUD. When utilized, the HFDS increases flight deck situational awareness through the combining of the visual environment by flying head up with aircraft parameters in field of view that are normally available only head down.

The advanced Sextant FMS has the ability to add to or reduce the flight deck work load. Adding to the flight deck work load inhibits the situational awareness. The advanced Sextant FMS has the ability to reduce and simplify the flight deck efforts associated with placing and keeping the aircraft in the desired place, at the right time, in the right configuration. The "4D" trajectory capable FMS computes the full trajectory from origin to destination. Additionally, a well defined flight path corridor is provided with demonstrated accuracy exceeding required navigation performance (RNP) > 1, 95 per cent.

The Sextant GCAS/TAWS is a primary means of making terrain "visible" to the flight crew when it may not be "visible". By "visible" is meant terrain that is mentally accounted for by the flight crew and a safe plan of action has been formed or activated that takes into account the terrain. Although GPWS introduction brought reductions in CFIT accidents, there were limitations to the equipment. TAWS is aimed at improving the GPWS approach and the two systems combined will detect a conflict with terrain on a normal approach and landing. This key element of GCAS functionality is the unique approach and landing "tunnel" that filters alerts upon "predicted correct" landing criteria during a normal approach and landing.

British Airways posed the question: has EFIS delivered? and considered whether the introduction into the flight deck of modern digital technology has been beneficial to the level of flight crew situation awareness. In extreme situations, the limitation imposed on what is "relevant" and kept in awareness can be quite severe. A great deal of skill in prioritising what is kept uppermost in a pilot's mind becomes vital in such circumstances. One has to ask whether the modern cockpit has been designed to encourage physical and cognitive exploration, such as selection of devices and sources of data and risk assessment.

British Airways Human Factors Reporting programme complements the Air Safety Reporting Programme (ASR) and the Flight Data Recording Programme (SESMA). Human factor (HF) reports are analysed by trained volunteer flight crews. Three factors combine to offer a complete representation of situational awareness as used in the HF reporting analysis process: environment awareness; mode awareness; and system awareness.

Figure 2 Situation awareness factors for glass and steam fleet group

Positive and negative assignment of SA factors was made in this assessment of the relative frequency of these factors in the modern (glass) and previous generation (steam) fleets. Figure 2 shows the percentage positive SA factor assignments for the glass and steam groups, for the three factors and adds a composite of all three. This and other studies do not support the contention that SA in the glass cockpit is better than in the steam. There are several explanations suggested for this. One is that automation has not only relieved the pilot of the necessity of manually controlling the aircraft but has also largely replaced the need to undertake any monitoring or navigational activity. It has been argued that SA depended on a process of both physical and cognitive exploration of the "world". By creating an expectation that all necessary information will be automatically presented to the crew, automation may have reduced the will to undertake the activities that would turn the display of data into useful information and knowledge. Hence, an extensive reassessment of the content of pilot training programmes may be required, and also of airlines' standard operating procedures, to overcome the deficit in SA and the skills that support it.

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