KOREAN AIR FLIGHT 801 CRASH A CASE STUDY

KOREAN AIR FLIGHT 801 CRASH: A CASE STUDY Vidyadhar Rangojoo EE 585: Fault tolearnt Computing 1

The Incident…. n Korean Airlines Flight 801 crashes into terrain on approach to Won Pat Int’l airport, Guam. The impact site lies at 658 ft on Nimitz Hill. n Death toll: 237. Survivals: 28. n Classified as a Controlledflight-into-terrain (CFIT) accident. EE 585: Fault tolearnt Computing 2

Wreckage of Flight 801… Ariel view of the location of crash EE 585: Fault tolearnt Computing Crash site 3

Wreckage of Flight 801…CONTD KAL 801 after the crash Ariel view EE 585: Fault tolearnt Computing 4

Reasons for the crash… n • • § • • Complex combination of events: Glide slope not operational. Pilot error. Inhibition of Minimum Safe Altitude Warning System: Ground based controller. Alerts controllers visually/aurally when tracked flight descend below a predetermined min safe altitude. EE 585: Fault tolearnt Computing 5

Reasons for the crash (CONTD) n FAA changed a safety critical system without reexamining the scenario the system addressed. n FAA allowed Guam to operate normally despite having two safety-critical systems out of service. EE 585: Fault tolearnt Computing 6

MSAW General Monitoring Minimum Safe Altitude (MSA) 500´ Threshold Terrain Clearance Altitude EE 585: Fault tolearnt Computing 7

MSAW System Overview… n n n 1990: System configured to monitor area within 55 -nm radius of the Guam radar. 1993: New system installed; citing frequent nuisance warnings issued by system. This change reduced MSAW processing to a 1 -nm ring b/w 54 and 55 nm from radar facility. New MSAW software installed at Guam to update terrain database; includes the inhibition zone. Facility Inspection of this software failed to note MSAW inhibition entirely. EE 585: Fault tolearnt Computing 8

The Guam MSAW Inhibition zone… MSAW Service Area Boundary (55 nm) Inhibit Zone (54 nm) Guam Pacific Ocean EE 585: Fault tolearnt Computing 9

Analysis… n The glideslope for runway 6 L was out of service, captain lost awareness of flight’s position on final approach. n Altitude callouts by onboard GPWS ignored bye flight crew; mistaken for nuisance messages over Guam. n Poor illumination surrounding Nimitz Hill. EE 585: Fault tolearnt Computing 10

Effectiveness of MSAW…. n NTSB/FAA simulation indicated that, without the inhibition, MSAW would have generated an alert 64 seconds before impact. n NTSB: This would have been sufficient for the controller to advise KA 801. n NTSB concluded that FAA’s quality assurance of MSAW was inadequate. EE 585: Fault tolearnt Computing 11

Lessons learnt…. n n Configuration management. Human error. EE 585: Fault tolearnt Computing 12

Related Incidents… n n Dulles International Airport, 1994. Houston Intercontinental Airport, 1998. EE 585: Fault tolearnt Computing 13

References. . n Paper titled “What should aviation safety incidents teach us? ” by John C. Knight. Paper titled “Framing analysis of software failure with safety cases “. William S. Greenwell, John C. Knight. http: //www. cnn. com/WORLD/9708/10/guam. crash/ n http: //ns. gov. gu/guam/indexmain. html n n EE 585: Fault tolearnt Computing 14