According to the NTSB, the airplane entered clouds almost immediately; its flight track began to waver slightly about seven minutes after takeoff, likely because it was being hand-flown in IMC: "The flight track remained generally on course toward the destination airport as the flight progressed, and there was no indication of an attempt to return to the departure airport." The airplane flew through the mountainous terrain in IMC consistently about 2500 feet below the
maximum elevation figure of 12,500 feet msl shown on the pertinent sectional chart.
If you're not sure what type of terrain you're flying over, look at AIM Figure 5-6-3 (camouflaged in with the ADIZ boundaries), or you could subtract the
Maximum Elevation Figure (MEF) on the sectional from the local Off-Route Obstruction Clearance Altitude (OROCA) and see if you get 2000 feet or 1000 feet.
This number is the
maximum elevation figure (MEF) for the highest known obstacle or terrain (with some added fudge factors) in that quadrangle, represented in thousands (the big numeral) and hundreds (the superscripted numeral) of feet.
The Las Vegas sectional current at the time of the accident depicted the
maximum elevation figure (MEF) in the area as 9400 feet msl; the accident site was located at 8869 feet msl.
Another valuable piece of info on sectionals often overlooked when considering night operations is the
maximum elevation figure (MEF) printed within each lat/long grid box.
Sectional charts include a
Maximum Elevation Figure (MEF), an example of which is shown at right.
The first step when considering a flight through high country is to pull out the local sectional and check out the
Maximum Elevation Figures (MEFs).