1.10.3.1 The Nonprecision Runway 6L Instrument Landing System Localizer-only (Glideslope Out) Procedure
The execution of the Guam ILS runway 6L localizer-only (glideslope out) approach requires the use of the NIMITZ VOR as a step-down fix[1] between the final approach fix (FAF) and the runway and DME to identify the step-down points.[2] The DME is not colocated or frequency paired with the localizer transmitter (which is physically located at the airport); rather, it is colocated and frequency paired with the NIMITZ VOR. The nonprecision localizer-only approach requires the use of the localizer to obtain lateral guidance to the runway, the DME to identify the step-down points, and the VOR to identify the final step-down fix to the MDA. According to Jeppesen Sanderson's August 2, 1996, 11-1 ILS Runway 6L approach plate, the airplane should cross the FLAKE initial approach fix (IAF)--located at 7 DME from the VOR--at or above 2,600 feet msl.
The nonprecision approach procedure prohibits descent below 2,000 feet msl (1,744 feet above airport elevation) before reaching the outer marker identified as GUQQY, which is the FAF and is located 1.6 DME from the VOR. Upon crossing the FAF, the procedure prohibits descent below 1,440 feet msl (1,184 feet above airport elevation) until passing the VOR. The procedure calls for a descent to 560 feet msl (the MDA, 304 feet above airport elevation), and the pilot is required to count up from less than 1 DME, as the airplane passes over the VOR, to 2.8 DME, the published missed approach point (MAP) and location of the middle marker. If a missed approach is not required, the airplane can continue its descent to the runway 6L threshold, located 3.3 DME from the VOR.
According to the FAA, the DME and localizer at Guam are now frequency paired and colocated. In addition, the August 27, 1999, Jeppesen instrument chart for the ILS runway 6L approach (which became effective on September 9, 1999) states "DME or RADAR required" and includes "ILS DME" in the frequency box.
1.10.3.2 Instrument Approach Charts for Guam International Airport
During postaccident examination of the cockpit area (which had separated from the main wreckage, as discussed in section 1.12), investigators found a clear plastic sleeve, measuring approximately 8 ½ by 11 inches, that contained the following Jeppesen approach charts for Guam International Airport, all of which were dated January 19, 1996: 11-1, ILS Runway 6L; 13-1, VOR Runway 6L; 13-2, VOR DME Runway 6L; 16-1, NDB Runway 6L; and 16-2, NDB DME Runway 24R.[3]
- ↑ The Safety Board is not aware of any other approaches that use a VOR as a step-down fix on the final approach segment of a localizer-only approach.
- ↑ 60 The step-down approach technique requires pilots to cross specific navigational fixes at or above several altitudes while descending to the MDA, at which point the pilot either executes a landing or a missed approach. 59
- ↑ Copies of these approach charts are contained in the Safety Board's public docket for this accident. The Board maintains a public docket for each accident it investigates. The docket is used to establish the permanent record of an accident.
