Instruments in Aviation

One of the things in aviation that stand to benefit from a redesign is aircraft
instruments, specifically the displays of those instruments. The “six-pack” – airspeed
indicator (ASI), altitude indicator (AI), altimeter, turn coordinator (TC), heading indicator
(HI), and vertical speed indicator (VSI) – play an extremely important role in the control of
the aircraft; they are the means of communication between aircraft systems and a controller
(Pallet, 2009). For a controller to have maximum control of the aircraft while minimizing the
mental effort involved in interpreting data, it is necessary to pay close attention to the form
and content of the data display.
Traditionally, aircraft system information has been displayed using the circular scale
(see the image of an altimeter in Figure 1); this is considered the classical form of
quantitative displays. However, circular scales have several limitations, the main one being
the accuracy with which data are interpreted (Pallet, 2009). Taking the altimeter in Fig. 1 as
an example, reading a whole value such as 2, 4 or 6 would be straightforward. However, if a
controller was to read a value 4.7 accurately and in the least possible time, that would be
quite difficult. Errors would compound such difficulty due to parallax: accuracy errors occur
when an instrument is read from an angle.

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Fig.1: A circular-scale altimeter
These shortcomings of the circular-scale display can be easily overcome by
redesigning the altimeter to have a digital display, such as the one pictured in Figure 2. In a
digital type of display, also known as the veeder-counter type, data are presented as alpha-
numeric, that is, in the form of numbers and letters. In aviation instrumentation practice, the
number presentation is the most prevalent. A numeric presentation of data overcomes the
above-discussed shortcomings by making it easy for a controller to read any value and at
whatever angle without having to worry about parallax.

Fig. 2: A digital display altimeter

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Reference

Pallet, E. (2009). Aicraft instruments: Principles and applications (2 nd ed.). Noida: Dorling
Kindersley (India) Pvt. Ltd.