Safety in Avionics: It Ought to Be in Pictures

By David Evans | September 1, 2000
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Flight mode confusion is perhaps the greatest bane of modern "glass cockpit" aircraft. One possible solution may be to substitute "pictograms" for letters and numbers. At least, this is the thesis of Flight Lieutenant Mark Walmsley of the Royal Australian Air Force (RAAF).

He has literally redesigned the flight mode annunciator (FMA) displays for the Airbus A320, a state-of-the-art computerized aircraft. He now is polling pilots, asking for their comments on his proposed displays. Specifically, his survey posits a basic question: Do graphic displays offer a cognitive advantage over alphanumeric presentation of the same information?

Walmsley’s survey forms part of a master’s thesis he is undertaking in collaboration with the International Test Pilots School in Coventry, UK, and the faculty of engineering at Bristol University, Bristol, UK. He is currently a test pilot with the Aircraft Research and Development Test Unit at RAAF Base Edinburgh in South Australia. He’s flown more than a dozen different aircraft, from the B777 to the Embraer ERJ-135 regional jet. "I found the FMA’s on all of them to be less than ideal," he said, "hence the thesis topic."

"Mode confusion" has been a factor in a number of high-profile crashes and, doubtless, a far greater number of unreported incidents. Indeed, a growing body of literature documents problems with automation feedback–a "revenge effect," so to speak–associated with the growing complexity of computer systems. The A320 illustrates the proliferation of modes. Multiple modes are common on Boeing’s computerized jets, too, but Walmsley offers the A320 to make his point, as he’s flown the airplane, and as he said in a telephone interview, "I have the most information and experience on the Airbus types."

The airplane features 11 autothrust modes, 17 vertical flight path modes, 10 lateral flight-path modes, and three combined modes (land, flare, rollout). There are complex interactions between these modes, not to mention arming/disarming and engagement/disengagement conditions. "An example of this is the airspeed control which can be via thrust modulation, flight path changes, or both simultaneously, depending upon the overall automation mode," Walmsley wrote in a draft of his thesis. "This issue is further complicated by the use of managed and selected modes in which [basically] either the flight management system [FMS] or the pilot controls the automation," he added.

Walmsley presents the FMS as a metaphysical swamp. As a possible first step in draining the swamp, he focused on a redesign of the flight mode annunciator (FMA) displays. These are located along the top of the primary flight display (PFD), which is located directly in front of the two pilots.

As Walmsley explained, the flight mode annunciators are arrayed in five columns, reading left to right, covering (1) autothrust system functioning, (2) vertical automation modes, (3) lateral automation modes, (4) instrument approach information, and finally, (5) the engagement status for the autopilot, flight director and autothrust system. The fifth column is a pure "is it turned on or off?" Hence, the fifth column shows whether the autothrust system is activated; the first column shows what it’s doing.

In the current system, Walmsley offers illustrations of four different descent modes. They do not form a sequence but rather are presented as separate images. When viewing these displays, Walmsley suggests, "consider the chance of confusing different descent modes."

Item No. 1 in the present design shows what the pilot will see in the descent mode with autothrust engaged and idle thrust selected. Altitude capture has been programmed for 5,000 feet, the flight management system is providing lateral navigation and the autopilot is engaged. The annunciators provide words such as "idle" and "AP1" for autopilot No. 1 engaged to illustrate the situation.

Now consider Walmsley’s suggested redesign. He combines in the top space of the primary flight display information that presently is displayed in three different locations: the PFD, the flight control unit (FCU) located on the glare shield, and the multifunction control display unit (MCDU) located on the center console between the two pilots.

Colors Add Information

Walmsley believes his redesign represents "a truth data summary on the current operation of the aircraft and the intended course of the automation." That is: What’s it doing now, and what’s it going to do next?

Perhaps the most significant aspect of his retooling from the existing display is the presentation of the vertical and lateral modes in graphic form, in which both the present and future states are shown. Colors add information. Walmsley presents a three-tier approach (blue, green, magenta) corresponding to different levels of automation. Blue is for manual flight (no automatics). Green is for normal automatic operation. Magenta is reserved for higher-order levels of automatic control, such as "when the FMS or MCDU is doing sneaky things like vertical flight path," Walmsley explained.

Walmsley offers a few examples of his concept. These "scenes" are not part of a sequence, but rather show separate images to illustrate the range of possibilities in different descent modes.

The New Design

Item No. 1 compares directly to the first case shown in the present design. However, the pictogram represents a difference that is immediately apparent:

When automation is being used, such as for autothrust or autopilot, a line box surrounds the applicable graphic. The box represents a computer, as in the notion that "the box is looking after" the function indicated. Thus, in this case, the box indicates that the autothrust is maintaining idle speed. It shows both the word "idle" and a symbol representing the throttle lever moved to the aft or idle position.

For, say, takeoff/go-around thrust, the letters "TOGA" would appear in the box and the lever symbol would be shown pushed to the right side of the box. When the automatic function is engaged, the pilot sees the box and related symbology in green. In the manual mode, there is no box and the symbology is in blue. Also, as the power setting changes, the little throttle symbol moves as the words "idle, climb, max" appear inside the box.

An airplane icon with the nose tilted down clearly shows that a descent mode is currently in operation, in this case with a constant 250-knot speed, which will be maintained by modulations in pitch attitude. As shown, the system is programmed for altitude capture at 5,000 feet, thereby showing both the present and future state in one simple graphic.

The top-down view of the airplane symbol with the word "NAV" shows that the MCDU has been selected as the lateral navigation source, i.e., navigation in the horizontal plane. The continuous line indicates there is no planned transition to another mode.

The box around "AP1" shows that autopilot No. 1 is engaged. When both autopilots are engaged, a double box would appear around the text.

From this redesign of the flight mode annunciator displays, Walmsley developed a survey to assess pilot preferences. To be sure, the static pictures presented in his survey and duplicated here do not represent the displays under dynamic conditions. Nor were survey respondents under any pressure or workload. These limitations aside, the initial batch of respondents expressed a clear preference for the pictogram-type displays. Among the comments, pilots said "automatic mode transitions are more obvious," and that the graphical displays improved situational awareness.

It would seem that Walmsley, as apostle of pictograms, is pointing the way to greater safety through improved avionics displays. The path he suggests sure seems to lead out of the underbrush of mode mystification to the high ground of mode mastery.

(Note: Those desiring to participate in Walmsley’s survey can find an electronic version at this Website: Or contact Walmsley by e-mail at [email protected].

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