1.   NTSB records also show that the pilot failed to keep the plane aligned with two basic directional transmitters, called the glide slope and the localizer.

2.   Pilots prefer those anyway, for passenger comfort, and they may become a standard way to land at fields without glide slopes.

3.   That makes the rare confrontation with an out-of-service glide slope more difficult, Roberts said.

4.   The cockpit voice recorder, though, records crew members questioning whether the glide slope was operating.

5.   The crew acknowledged the transmission but not the information on the glide slope.

6.   The Guam airport did not have a working glide slope that night because it had been taken out of service for maintenance.

7.   A landing system known as the glide slope, which leads planes to the runway, had been out of service at the airport.

8.   Many airports, however, do not have glide slopes and pilots use other landing methods.

9.   Many airports, however, do not have glide slopes and pilots use other methods for landing planes.