To the Editor:

Re “Pilots Followed Boeing Checklist Before Crashing” (front page, April 5):

Sensor failure is one of the most common causes of accidents. In the power and chemical industries, the following control strategy has reduced the number of such accidents a hundredfold.

For all critical measurements, we use three sensors employing different principles for their operation, and whenever the reading of one disagrees with the other two, it is disabled, while the system continues operation using the average reading of the remaining two detectors.

Whenever this occurs, the operator is alerted, and the computer automatically releases the system for human override.

Béla Lipták
Stamford, Conn.
The writer is the editor of the Instrument and Automation Engineers’ Handbook.

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