Already a member? Please login below for an enhanced experience. Not a member? Join today
Menu

Proficient Pilot: Losing controlProficient Pilot: Losing control

Display a stall-speed solution

A hot-button topic these days is “loss of control” (of a perfectly good airplane). The NTSB has identified LOC as the number one cause of aircraft accidents across all segments of aviation (general aviation, airline, corporate, and military). As we are well aware, the most common cause of such accidents is an inadvertent stall that occasionally leads to a spin, a problem haunting aviation ever since the pioneers began flying gliders in the late nineteenth century.

Given that pilots are so well aware of the hazards of stalling, it is natural to wonder why stall/spin accidents continue to occur with such regularity. One reason might be that modern training seems to deemphasize basic airmanship in favor of spending more time learning to use sophisticated avionics and instrumentation. As a certified member of the Society of Ancient Pelicans, I remain convinced that the best way to learn to fly is in a taildragger with minimal instrumentation.

The new generation of airspeed indicators and altimeters, however, might also be contributing to the problem.

There was a time not long ago when digital speedometers and wristwatches were the rage. Analog instrument displays went the way of the dodo bird. But then a strange thing happened. Automobile and watch manufacturers reverted to providing analog displays; digital displays were phased out.

The primary reason for this reversal is that it was discovered that analog indications are more intuitive than digital displays, and this makes it easier for the user to visually process relative values. For example, a quick glance at a digital speedometer might show that you are traveling 59 mph, but an analog or graphical display would show that you are approaching a 65-mph speed limit. This is especially true for a pilot who mentally processes and absorbs the sweeping motion of analog indicators to obtain a sense of the rate at which speed (or altitude) is changing.

The same applies to telling time. A digital clock will display 9:50 when an analog display shows that it will be 10 o’clock in 10 minutes. For most of us, the relative position of the hands provides data that is easier to process.

Could this difference in the way we process digital and analog data be a factor in causing some LOC accidents? It might be, especially for those of us accustomed to conventional (analog) airspeed indicators and altimeters. The digital presentation of airspeed and altitude on glass panels (primary flight displays) is not as intuitive. It does not allow us to process changes as easily or as rapidly as do steam gauges. Wouldn’t it be nice if the manner in which airspeed and altitude is presented on a PFD were made to emulate steam gauges? This would only require a software change and, I think, simplify the task for pilots of detecting, understanding, and controlling airspeed and altitude changes.

I would like to propose another change, and that is to add a second needle to airspeed indicators. The “green” needle would be conventional and simply point to indicated airspeed. The “red” needle, however, would indicate stall speed at any given time and condition, something that could easily be determined by electronically and automatically inputting the following factors: VS, aircraft weight, center of gravity, flap position, and G load.

Assume, for example, that an aircraft is being flown at an indicated airspeed of 110 knots (indicated by the green needle). The red needle might indicate, say, 57 knots, the stall speed at that time. The aircraft then rolls into a turn, and the increasing G load causes the red needle to move higher. The steeper the turn, the greater would be the stall speed. A pilot would know his safety margin above stall at any given time by the separation between the green and red needles. If they get too close, the pilot knows that he needs to reduce bank angle and possibly lower the nose. The split between the needles would then widen. In any event, maintaining separation between the needles would prevent a stall at all times. Knowing the stall speed at any given time would make stalling easier to avoid.

I am not an engineer, but discussions with a few of them indicate that such a presentation would not be difficult to provide. As a matter of fact, such an airspeed indicator does not have to be incorporated into a PFD. It could be developed and substituted for conventional airspeed indicators in any airplane with an electrical system.

Would this suggestion reduce the incidence of stall/spin accidents? I would like to think so. In any event, simply observing the movement of the red needle while maneuvering and flying through turbulence, for example, would certainly be educational.

Web: www.barryschiff.com

Barry Schiff

Barry Schiff

Barry Schiff has been an aviation media consultant and technical advisor for motion pictures for more than 40 years.

Related Articles