bubbers44:
Sinatra's mothers Lear out of Palm Springs was before his Las Vegas show when they turned west into the mountains so must have been in the early evening.
It was daytime, but IMC in rain with one of those big systems that occasionally affects KPSP.
In those days KPSP had a non-radar approach control. The clearance was somewhat complex via airways to Goffs VOR; in other words generally to the east. The initial assigned altitude as 9,000, which was plenty safe for the cleared route of flight.
But, the crew were early generation "radar babies." The assumed they were getting vectors so they maintained runway heading (310) until they flew into the side of 11,500' Mt. San Gorgonio. A center supervisor was watching for them to show up on radar to the east of PSP and he realized something was terribly wrong. But, the Lear was still with KPSP non-radar approach control. The supervisor got on the direct line to approach control and shouted, "Tell them to immediately climb to 14,000!"
Alas, it was too late. They impacted 9,000' terrain some 20 miles NW of the airport.
BTW, earlier the KPSP approach controller asked them to report crossing a couple of radials, which would have confirmed they were on the assigned easterly routing. I believe the crew reported those radials even though they couldn't have possibly crossed them on runway heading.