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Throughout the approach, the flight crew failed to follow approved company approach procedures. The first officer‘s failure to activate and identify the ILS frequency at the appropriate point in the approach prevented the pilots from receiving glideslope and localizer information on their EADIs until late in the approach. Further, the pilots‘ failure to engage the APR mode on their flight directors after the ILS frequency was selected prevented them from receiving flight director guidance. In addition, neither pilot was adequately scanning the cockpit instruments. Compliance with standard company procedures, activating and identifying the ILS frequency and subsequently the APR mode, and adequate monitoring of the flight instruments would likely have prevented the accident.
Fatigue might have also played a role in the flight crew‘s degraded situational awareness. According to the captain‘s wife, on the night before the accident, the captain received about 4 hours less sleep than normal. A company employee stated that, when the captain arrived for work on the morning of the accident, he looked as though he had just woken up. The first officer‘s wife stated that the first officer did not have regular sleeping hours and that she was not sure how much sleep he got the night before the accident. Although the early reporting time for the accident flight might have resulted in flight crew fatigue, the actual amount and quality of sleep received by the captain and the first officer could not be determined. Regardless, their improper conduct of the approach reflected fundamental operational shortcomings that were independent of fatigue.

Minimum Safe Altitude Warning Operation

The Safety Board evaluated the airplane‘s flight profile and the MSAW algorithms for the HOU airport area and determined that the MSAW performed as designed given the alert thresholds established for the HOU airport area. The study determined that the accident descent profile was along the edge of the MSAW GTM predicted alert threshold. In this case, although the MSAW recorded a single predicted exceedance of the threshold at 0614:30, the two subsequent scans did not predict exceedances; therefore, no GTM predicted alert was generated.
The MSAW generated an AM current alert at 0614:35. The HOU ATCT controller began issuing a low-altitude warning to the flight crew about 7.5 seconds later. Analysis of the MSAW‘s performance found that the system provided only about 11.5 seconds of warning time before the airplane struck the light pole, which was not sufficient time for the controller to recognize the alert and warn the flight crew in time to prevent the accident. Configuring a single set of MSAW parameters is a balancing act between minimizing —nuisance alarms“ and providing sufficient warning time. Implementing software and adaptation modifications to minimize or eliminate unwarranted MSAW alerts without degrading the usefulness and safety benefit of MSAW will increase the credibility and overall effectiveness of MSAW warnings. Such modifications will likely improve controllers‘ ability to detect hazards and potentially prevent controlled flight into terrain accidents. As noted previously, in July 2006, the Safety Board issued safety recommendations to the FAA that addressed MSAW alert effectiveness.

PROBABLE CAUSE
The National Transportation Safety Board determines that the probable cause of this accident was the flight crew‘s failure to adequately monitor and cross-check the flight instruments during the approach. Contributing to the accident was the flight crew‘s failure to select the instrument landing system frequency in a timely manner and to adhere to approved company approach procedures, including the stabilized approach criteria.
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本文鏈接地址：Crash During Approach to Landing Gulfstream G-1159A (G-III),(15)