absence of the CERAP controller's procedural errors, singularly or in any combination, would have prevented the accident or reduced its severity. However, the Safety Board concludes that strict adherence to ATC procedures by the CERAP controller may have prevented the accident or reduced its severity. Therefore, the Safety Board believes that the FAA should develop a mandatory briefing item for all air traffic controllers and ATC managers, describing the circumstances surrounding the performance of the CERAP controller in this accident to reinforce the importance of following ATC procedures.
2.6.2 Intentional Inhibition of the Minimum Safe Altitude Warning System at Guam
Since February 1995, the Guam ARTS IIA MSAW system[1] had been intentionally inhibited by the FAA from providing low-altitude alerts inside a 54-nm ring around the ASR-8 radar antenna. The system was inhibited because it had been generating what air traffic controllers believed to be numerous false alerts, or "nuisance warnings." Thus, at the time of the accident, the MSAW system was only available (uninhibited) in a 1-mile-wide band around the ASR-8 radar site, between 54 and 55 nm. Korean Air flight 801 crashed approximately 3 nm southwest of Guam International Airport in an area of rising terrain that would have been covered by the MSAW system if it had not been inhibited.
FAA technical staff and Safety Board investigators conducted a postaccident simulation using the original parameters intended for the system. The simulation results indicated that, if the MSAW system had not been inhibited inside the 54-nm radius, both a visual and aural low-altitude alert would have been generated on the ARTS IIA monitors in the CERAP facility about 0141:22, as the airplane was descending through 1,700 feet msl. Accordingly, the Safety Board concludes that, if the ARTS IIA MSAW system had been operating as initially intended, a visual and aural warning would have activated about 64 seconds before flight 801 impacted terrain, and this warning would have likely alerted the CERAP controller that the airplane was descending below the minimum safe altitude for that portion of the approach.
Flight 801 was under the control of the Agana tower controller at the time that the low-altitude MSAW alert would have been issued by the ARTS II system in the CERAP facility. The Agana tower was not equipped with a functioning terminal radar display. Therefore, for the crew of flight 801 to have received a low-altitude advisory, the CERAP controller (who was still responsible for monitoring the airplane after he initiated a frequency change to the tower controller) would have had to relay the alert to the tower controller, who would then have had to convey the alert to the flight crew. Given the prevalence of CFIT accidents, controllers would be expected to vigilantly monitor the system and provide timely notification to either another controller or a flight crew when
- ↑ Although the CERAP controller told Safety Board investigators that his last observation of the target of flight 801 on the terminal radar display was when the airplane was 7 miles from the airport at an altitude of 2,600 feet, FDR and radar data do not support his statement. The data indicated that, when the CERAP controller instructed the flight to contact the Agana tower, the airplane was at an altitude of about 2,200 feet and maintained a continual descent. Therefore, the airplane was probably farther than 7 miles from the airport when the CERAP controller last observed the flight.
