The aircraft cockpit has progressed from round-dial steam gauges that supplied basic information to iterative multi-color, multi-function displays capable of giving the aircrew more information than they can absorb. What are the implications of this technology when considering causation factors?
Round dials had two restrictions: they could display only limited information and, whether the information was necessary or not, the space occupied by that dial could not be used for anything else. Today, engineers can arrange a myriad of information on multiple displays as needed. Airspeed, for example, can be displayed on any display as a re-created “round dial”, as a tape, digitally, in true, calibrated, indicated, or corrected formats, up and down, left to right, anywhere on the display, or in multiple formats in multiple locations in any color. The method of presentation can change as a function of rate of change, mode of flight, or as desired. Lines, circles, squares, text, or symbols can blink, flash, be any color, change color, be multi-colored, be any width, size, shape, or texture.
Who decides how, when, and where to display information? How is the decision made as to how much information is an overload? Who decides what is most important, and the best way to display it?
On January 20, 1992, Air Inter Flight ITF148 crashed near Strasbourg-Entzheim Airport, France, killing 87 of 96 occupants. The aircrew was cleared for approach using a 3.3° angle of descent (5.5% glide slope or about 800 feet per minute descent). Thinking the FCU (flight control unit) was in TRK/FPA (track/flight path angle), they programmed in “3.3”. The FCU was actually in HDG/V/S (heading/vertical speed) mode, and “3.3” meant 3,300 feet per minute rate of descent, four times the desired rate of descent. Because the aircraft was in the clouds and there was no onboard GPWS (ground proximity warning system), the crew was not warned and the airplane crashed about 3 miles short of the airport.
Pilot error? Design defect? Sensory overload? Perhaps all of the above.
On April 8, 2000, a high-technology MV-22A crashed near Marana, Arizona, killing 19 U. S. Marines. The aircrew was attempting to descend rapidly while flying at a slow airspeed. In a phenomenon called “vortex ring state,” a helicopter descending rapidly at a slow airspeed, such as this MV-22A, creates its own atmosphere by re-ingesting the air it has just displaced. This leads to incipient blade stall because of increased angle of attack on the rotor blades. Roll in the MV-22A is accomplished by dissimilar lift of the two rotor heads. When the pilot attempted to roll the aircraft, the increased pitch on that set of rotor blades caused them to completely stall, and the aircraft rolled in the opposite direction, so rapidly that the aircrew, unaware of what was happening, had no chance to correct. The digital flight control system had not been programmed to recognize a roll opposite to the desired direction as a malfunction and did not revert to manual or provide a warning.
Pilot error? Design defect? Sensory overload? It can be argued that it was all of the above.
In today’s high technology environment, those who investigate aircraft crashes must expand their investigations into diverse areas that require unique knowledge and experience. The expanding use of computers and exotic materiel in flight control surfaces and systems, cockpit design, fuel control systems, engines, and other critical aircraft systems has forever changed the scope, methods, landscape and texture of investigations.
The cockpit is unique in that it is the only interface between aircrew and machine. With the exception of the “seat of the pants” feeling, everything the pilot knows and does takes place by virtue of that interface. The degree of ease or difficulty the aircrew experiences in controlling the aircraft and its systems is dependent on the design of the cockpit. I suppose it should be noted that other things can create difficulty or make flying easy. For example, dynamic stability and control make a huge difference in whether the pilot can relax during the flight. If you do not understand that, go rent something like a Dehavilland Tiger Moth and see what it’s like to have to be on the controls 100% of the time.
But… back to the cockpit. How is the modern cockpit designed? In many cases, aircraft manufacturers choose a pre-developed design for incorporation in their airframe. We all know of aircraft that come equipped with various Brand Name systems that have proven capabilities. Cockpit equipment manufacturers optimize their products to be adaptable in multiple platforms.
The military, of course, is an exception, as are almost all “expensive” aircraft. The cockpits of these machines are designed by human factors, ergonomics, computer, environmental, and engineering experts who combine their talents in an attempt to produce the most user-friendly and capable cockpit for the least money.
But probing deeper, how is that done? All of us can think of some of the products of these designers. The color “red” is used for warnings. Why? Human factors says red has the longest wavelength, does not mask other colors when the rods in our eyes are exposed to it, and produces the strongest reactions. Some gauges have always been larger than other gauges because the information produced is deemed to be more important, depending on the application. For example, while a vertical speed indicator (VSI) in an airplane may be a mid-size instrument, it is often the largest in a glider because sensing climb rate is so crucial. One of the more important designs in aviation was called the “basic 6”, later called the “basic T”, that was developed in 1937 to optimize the pilot’s scan pattern.
When it comes to multi-color, multi-function displays, the skills of the designers are fully brought to bear. They tend to provide all the information they can. So what’s wrong with that? What’s wrong is that the pilot may not be able to use it all. Pilots find it difficult to admit, but they are human and have limitations. The human brain is capable of a great deal, but it can absorb only a certain amount of detail. Those who flew fast-movers into North Viet Nam will remember that the warnings produced by all of the electronic countermeasures were often so distracting, loud, confusing, and simply over-powering that the question of “good vs. bad” often arose. Some pilots simply turned off all of their aircraft’s warning systems.
Most “modern” cockpits are designed with declutter functions. A pilot can push a button and eliminate certain classes of information from the display to focus in on what is most important.
Certainly it is possible to give the pilot less information than is needed. Remember flying partial panel? The optimum was often just keeping the blue side up and the compass pointed into the same quadrant. But is it possible to give the pilot too much information? So much information that he can’t easily scan the most important data. So much information that he may misinterpret what he thinks he sees or has done.
When is less more? Food for thought.
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Colonel lawrence again provides us with great insight based upon his years as an engineering test pilot and cockpit human factors expert. His comments took me back to a crash in the United Kingdom when the aircraft sustained an engine failure but the flight crews’ instruments were not clear as to which engine had failed (once they throttled back both engines upon feeling severe vibration). On the other side of the spectrum, sometimes there is too little instrumentation. For example, the FAA still allows manufacture of Eurocopter helicopters with LIGHTS instead of gauges. This shortcoming led directly to the crash of an AS-355 and the death of its pilot. It would have taken very little money or effort to at least put an old but reliable pressure gauge in that cockpit.