Appendix D 69 APPENDIX D. COMMERCIAL, MILITARY, AND EXPERIMENTAL AIRCRAFT
ACCIDENTS D.1 Commercial And Military Software Failures.
The space vehicle failures described here discuss incidents resulting in mission failures or anomalies without impacts to the uninvolved public. However, such incidents illustrate the importance of software and computing systems in the operation of space and launch vehicles. Unfortunately, software has been a cause of several accidents resulting in injury and loss of life in commercial and military aircraft. Some of those accidents are described below.
D.2 X-31.
D.2.1 An X-31 U.S. government research aircraft was destroyed when it crashed in an unpopulated area just north of Edwards Air Force Base while on a flight originating from the NASA Dryden Flight Research Center, Edwards, California, on January 19, 1995. The crash occurred when the aircraft was returning after completing the third research mission of the day. The pilot safely ejected from the aircraft but suffered serious injuries.
D.2.2 A mishap investigation board studying the cause of the X-31 accident concluded that an accumulation of ice in or on the unheated pitot-static system of the aircraft provided false airspeed information to the flight control computers. The resulting false reading of total air pressure data caused the flight control system of the aircraft to automatically configure for a lower speed. The aircraft suddenly began oscillating in all axes, pitched up to over 90 degrees angle of attack and became uncontrollable, prompting the pilot to eject.
D.2.3 The mishap investigation board also faulted the safety analyses, performed by Rockwell and repeated by NASA, which underestimated the severity of the effect of large errors in the pitot-static system. Rockwell and NASA had assumed that the flight software would use the backup flight control mode if this problem occurred.
D.2.4 Lesson Learned.
Estimating and mitigating software risks, including software used to mitigate hardware anomalies, are critical aspects of software safety (Dornheim 1995, Haley 1995).
D.2.5 References.
Dornheim, Michael A. “X-31 Board Cites Safety Analyses, But Not All Agree.”
Aviation Week & Space Technology, pp. 81-86, dated December 4, 1995.
Haley, Don. “Ice Cause of X-31 Crash.” NASA Dryden Flight Research Center, Edwards, California. NASA Press Release 95-203, 1995.
Appendix D 70 D.3 F-22 RAPTOR.
D.3.1 On February 11, 2007, a flight of 12 F-22’s, on their first deployment to Japan from Hawaii, encountered a multiple system failure at the International Date Line. When the fighters crossed the line, they lost all navigation and attitude indication systems, and parts of their communication and fuel systems including their radios. Fortunately, they were re-fueling at the time and were able to follow the tankers back to Hawaii. The errors were fixed in about 48 hours, and the planes completed their deployment following the software fix.
D.3.2 Lesson Learned.
Software should be tested across the entire environment in which it will operate (Defense Industry Daily, 2007).
D.3.3 References.
“F-22 Squadron Shot Down by the International Date Line.” Defense Industry Daily, 2007. http://www.defenseindustrydaily.com/f22-squadron-shot-down-by-theinternational-date-line-03087/.
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