- 37 -
white arc associated with the 10,000 feet pointer. This possibility is supplemented by the literature available regarding the various investigations of the readability of the three pointer altimeter which indicates it is the most susceptible to misreading of any of four types presently in use in commercial aviation.
Therefore, the Board believes that the crew for reasons unknown allowed the aircraft to descend below the assigned altitude of 6,000 feet and ultimately crashed into the water.
2.2 CONCLUSIONS
A. Findings
1. The known medical information concerning the flight crewmembers is not indicative of any pre-existing disease or inflight incapacitation.
2. Post mortem examinations indicate that there is no evidence of incapacitation or pre-impact injury to the crew.
3. There is no evidence of any system failure prior to impact.
4. The aircraft was approximately on the correct inbound course.
5. The cockpit VHF radio controls were set in a manner appropriate for a descent and approach to O'Hare.
6. The recovered altimeter had a setting that could have introduced an error of approximately 20 feet in the instrument reading.
7. Based on the identification of the captains voice on the ATC recording tape and common custom and practice in commercial aviation, it is believed the first officer was flying the aircraft.
8. The SAGE altitude reports referred to UAL 389 and recorded the altitude of the flight at 2119:54 as 2,000 feet with an accuracy of plus 500 – minus 1,000 feet.
