Aerospace
Fig. 3. Now upgraded with a more powerful 1600 Shaft Horsepower Pratt and Whitney PT6A-68D engine, the AT-6 is a structurally strengthened derivative of the proven Beechcraft T-6 trainer.
“For example, a COTS based device I was using was processing radar data, when some months later, intermittent and ominous readings from the device would appear on the display. Fortunately the controller identified the track data as an error. Had the mistake not been identified there was a real risk tracks would be labelled incorrectly. The COTS device was replaced, but this did not fix the fault. “Weeks of fault finding later it was discovered a replacement
cable interfacing the COTS device to the system was replaced at the time the failure occurred. The cable was within electrical specification but for one key difference, its length. The increased length of the cable had meant the software on the COTS device could not handle the increased periods of time it took to retrieve data, process it, and send it to the display. Instead it took its best guess and sent the data anyway.” COTS is an emotive subject for Chris Andrews, product
marketing manager at C-MAC Aerospace, who believes that in some ways, it is the enemy of his business as customers strive to cut costs by using commercial grade parts for harsh environment applications. He says: “It is hugely controversial
in the space market in particular, where the added issue of radiation tolerance hinders the life of electronics. A major producer of small satellites known for using COTS solutions has been highly successful at producing mini-sats using COTS electronics.”
Lot homogeneity
A key requirement for high reliability applications is lot homogeneity, continues Andrews. Even lots of semiconductors having the same date code may use chips from different wafer lots as the date code is sometimes applied after final test. In order to verify a lot of COTS components are fit for purpose, extensive dynamic and climatic testing is often required. This can end up costing more than the cost of high reliability parts thereby defeating the object. General Dynamics UK uses Escher Technologies’ Perfect
Developer (PD) to specify and design a safety-critical airborne stores management system. Guy Mason, senior software engineer at General Dynamics UK says: “Our need is to meet the requirements of defence standard 00-55 to Safety Integrity Level 4. Escher Technologies software met our requirements best. We were especially impressed by the automation of verification proofs, which will substantially reduce our costs, and by the level of support provided by Escher Technologies.” David Crocker, CEO of Escher Technologies, enlarges:
Fig. 4. The Airbus A350 XWB in flight, with RR engines. Thales has chosen the AdaCore GNAT Pro technology, including several safety-qualified tools, to develop critical systems for the new Airbus A350 XWB.
Photo courtesy: AIRBUS S.A.S. 2008 64
www.engineerlive.com
“PD has also been used at General Dynamics UK in conjunction with SPARK Ada, a formally-defined computer programming language based on Ada, and to make this easier we now provide partial generation of SPARK code from PD. “One of the problems with using COTS components for safety-critical software is that COTS software typically uses dynamic memory allocation, which has a number of problems in embedded systems and is usually forbidden in critical software. So the use of COTS at the higher safety integrity levels is typically confined to real-time operating systems and similar components that have been designed with safety in mind and certified.” ●
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