A Comparison of Full and Reduced-Alpha Keyboards for Aircraft Data Entry
Authors: Hornsby Mary E. 
Published: July 2017

CRT's and associated data entry keyboards are being used in aircraft to replace dedicated switches and instruments for entry and display of flight relevant data. This study compared the speed and accuracy of data entry using two different types of alphanumeric keyboards designed for entering data into aircraft mission computers.

A full-alpha keyboard has a separate key for each letter of the alphabet as well as each number; a reduced-alpha keyboard (e.g., telephone type) has more than one letter per key. Reduced-alpha keyboards generally weigh less and occupy less space than full-alpha keyboards, but these advantages might be nullified by operational disadvantages. Alpha entries on a full-alpha keyboard require only one stroke per letter, while alpha entries on a reduced-alpha keyboard require at least two keystrokes per letter: one to identify the correct key, and one or more to select the appropriate letter on that key. Because increasing the number of required keystrokes increases both entry time and the opportunity for error, it was hypothesized that alpha entries would take longer and be less accurate on a reduced alpha keyboard.

In this study, twelve subjects (eleven of them pilots) entered flight-related information on each of two keyboards. On the reduced-alpha keyboard, numbers and letters were arranged on a 3 X 4 key matrix, with three letters and one number on each key. The full-alpha keyboard had number keys arranged in a 4 X 3 matrix and letter keys (one letter to a key) in a separate 7 X 4 matrix. The keyboards were installed in similar flight simulators and were situated forward and to the left of the operator.

For both types of keyboards, entries appeared on the “scratchpad” line of a monochrome CRT just above the keyboard. For all entries on the full-alpha keyboard, this meant that the single number or letter on the selected key appeared on the CRT. For all entries on the reduced-alpha keyboard, the single number on the selected key appeared on the CRT scratchpad line. At the same time, the three letters on the selected key appeared just below the scratchpad line, and just above three unlabeled “alpha select” keys, which were physically distinct from the alphanumeric keyboard. Numeric entries were complete at this point; to finish an alpha entry, the “alpha select” key just under the appropriate letter had to be pressed.

After keyboard training and practice, each subject entered flight initialization information, a flight plan, and flight plan modifications for each of two “flights” using one of the keyboards. This required a total of approximately 80 alpha and 240 numeric entries. This procedure was repeated two days later on the other keyboard for two different “flights.” Order of keyboard and “flights” was counterbalanced. Performance measures were the average entry time (computer recorded) and the number of errors for alpha and numeric characters on each type of keyboard.

As expected, alpha entries were significantly slower on the reduced-alpha keyboard (x‾ = 3.84 sec) than on the full-alpha keyboard (x‾ = 2.28 sec), since they required two keystrokes. Contrary to expectation, numeric entries were also significantly slower on the reduced-alpha keyboard (x‾ = 1.70 sec) than on the full-alpha keyboard (x‾ = 1.18 sec). This result may have been due to the confusion involved in making two different types of entries (with different procedures) using the same set of keys for the reduced-alpha keyboard, while alpha and numeric entries were physically separate and identical in procedure on the full alpha keyboard.

Errors were minimal for both types of entries on both types of keyboards. A total of 26 errors in numeric entries were made on each type of keyboard. There were 30 alpha entry errors on the reduced alpha keyboard and nine on the full-alpha keyboard. There was no evidence of a speed-accuracy tradeoff in entries on the two keyboards since entries were faster and as accurate on the full-alpha keyboard. Whether the entry speed advantage of the full alpha keyboard would outweigh its greater size and weight would depend on design factors and the time criticality of necessary entries for a specific application.