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 flight checked, certified, and returned to service on August 31, 1997. The Safety Board's review of the facility maintenance log revealed no entries of pilot reports regarding the ILS or related navigation systems from July 7 to August 6, 1997.

The accident airplane's CVR recorded conversation among the flight crew regarding the operational status of the ILS glideslope as they approached the airport. For example, as previously stated in section 1.1, about 0139:55, the flight engineer asked, "is the glideslope working? glideslope? yeh?" About 0139:56, the captain answered, "yes, yes, it's working." About 0140:00, the first officer responded, "not useable." About 0141:46, the captain asked, "isn't glideslope working?"

In a postaccident interview, the captain of a Continental Air Micronesia 727-200 stated that, about 1530 on August 5, 1997, he was conducting an in-flight functional test of a newly installed global positioning system (GPS) when the airplane's instrumentation showed an indication of the ILS glideslope, even though the glideslope was out of service. Specifically, the captain stated that he was on approach to runway 6L at Guam International Airport and was centered on the localizer when he noticed that the glideslope was also centered and that no warning flags were associated with the ILS. In addition, the captain said that the glideslope always indicated "center" with no warnings even when the airplane was above the normal glidepath. The first officer confirmed the captain's observations. However, the flight crew did not indicate any anomalous glideslope indication to ATC personnel or submit any maintenance writeups containing such information.

The Continental Micronesia captain told Safety Board investigators that he originally assumed that the anomalous glideslope indication he experienced was caused by an airplane anomaly. The captain further stated that he thought the anomaly might have been a result of the GPS wiring installation. The captain did not report the glideslope anomaly to his chief pilot until 2 days after the Korean Air accident. The first officer stated that he and the captain "never thought twice" about the glideslope indications because they knew the glideslope was inoperative.

According to the maintenance records for the Continental Air Micronesia airplane, the first officer's ADI and HSI were removed and replaced on August 5, 1997, after the functional test flight. In addition, the records showed repeated squawks for the first officer's ADI and HSI between August 8 and 25, 1997.

Instrument approaches available for runway 6L at the time of the accident were the ILS (localizer only, glideslope out of service), the VOR/DME, and the VOR.