Pilots with their eyes taped

My colleague Steve Trimble has just taken up a favourite theme of mine in a post-Asiana crash article that’s just gone up in the FG Club site.

Why don’t pilots monitoring (usually the pilot-not-flying) actually monitor what’s going on? Or do they monitor but fail to intervene when they don’t like what they see?

Come to think of it, why has it frequently been clear – following recent accidents – that the pilot flying was not scanning the flight instruments properly? Or was he/she scanning but not understanding the significance of what’s presented?

When you have a moment, have a look back at an earlier entry in this blog: Asiana: one of several similar events.

I want to bring up a related issue that is hardly ever mentioned now, although at the time the modern, single-screen primary flight display (PFD) was introduced it was debated a lot.

It’s the issue of analogue displays versus digital displays, and moving tapes versus moving needles on dials.

The modern PFD got rid of analogue needles/dials for the air speed indicator (ASI) and the altimeter and replaced them with speed and height tapes. The new PFD also made the vertical speed indicator (VSI) almost invisible compared with how it used to be.

I have never met any pilot, including those at Airbus, Boeing, Bombardier and Embraer, who argue that a digital tape is more intuitive than an analogue display. Yet they went with tapes for the ASI and altimeter.

Reading a number presented in characters, and making sense of its value, is a conscious cognitive effort that takes a finite time.

A needle on a dial may point to numbers around the dial’s rim, but after a very short time on type you don’t need to read them any more – the position of the needle on the dial is your value. That takes far less cognitive effort than interpreting characters.

And the movement of a needle on a dial is instantly visible and far more intuitive than a sliding tape with numbers on it. Not only is the rate of change evident, the needle position is clear, and so is its relationship to the red sectors at either end of the airspeed envelope. What is more, the red sectors are visible at all times, not just when you are about to enter their realms.

Now that flightdecks are far less cluttered but provide far more data, there is plenty of physical room for analogue displays.

So come on, avionics manufacturers, let’s bring back analogue information. Pilot instrument scanning will receive an instant boost.

What’s more it could save lives by reducing loss of control accidents. Isn’t that sufficient incentive?

Incidentally, if you haven’t registered for the FG Club yet, you’re missing out. It’s free, but you can only see the content if you register. Find it on the Flightglobal.com home page now.



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