Aircraft Instrumentation. Aircraft Embedded Information Systems

Instrumentation of an aircraft means installing data collection and analysis equipment to collect information about the aircraft’s performance. Instrumentation equipment includes various recorders for collecting real-time flight parameters such as position and airspeed. Instruments also capture flight control inputs, environmental parameters, and any anomalies encountered in flight test or in routine flight.

One method of overcoming this limitation is to link flight instruments to ground recording systems, which are not limited in their data recording capacities. A key issue here is the bandwidth between the aircraft being tested and its ground (recording) station. This bandwidth is limited and places important limitations on what can be recorded.

This type ofdata link is also limited to the range of the link, limiting the aircraft’s range and altitude during this type of flight test. Aircraft computers are used both in processing the data as they are being collected on the aircraft and in analyzing the data after they have been collected.

Aircraft Embedded Information Systems. Embedded information system is the latest terminology for an embedded computer system. The software of the embedded computer system is now referred to as embedded information. The purpose of the aircraft embedded information system is to process flight inputs (such as sensor and flight control) into usable flight information for further flight system or aircrew use.

The embedded information system is a good example of the merging of two camps of computer science applications. The first, and larger, camp is the management of information systems (MIS). The MIS dealt primarily with large volumes of information, with primary applications in business and banking. The timing requirements of processing these large information records are measured in minutes or hours.

The second camp is the real-time embedded computer camp, which was concerned with processing a much smaller set of data, but in a very timely fashion. The real-time camp’s timing requirement is in microseconds. These camps are now merging, because their requirements are converging. MIS increasingly needs real-time performance, while real-time systems are required to handle increased data processing workloads. The embedded information system addresses both needs.

Aircraft and the Year 2000. The year 2000 (Y2K) was a major concern for the aircraft computer industry. Many of the embedded computers on aircraft and aircraft support functions were vulnerable to Y2K faults because of their age. The basic problem with those computers was that ayear was represented by its low- order two digits. Instead of the year having four digits, these computers saved processing power by using the last two digits of the calendar year.

For example, 1999 is represented as 99, which is not a problem until you reach the year 2000, represented as 00. Even with this representation, problems are limited to those algorithms sensitive to calendar dates. An obvious problem is when an algorithm divides by the calendar date, which is division by 0. Division by 0 is an illegal computer operation, causing problems such as infinite loops, execution termination, and system failure.

The most commonly mentioned issue is the subtraction of dates to determine time durations and to compare dates. The problem is not that the computer programs fail in a very obvious way (e.g., divide-by-zero check) but rather that the program computes an incorrect result without any warning or indication of error. Lefkon and Payne (11) discuss Y2K and how to make embedded computers Y2K-compliant.