Well in this case there were multiple failures... Should they have been identified earlier? Yes.

In general I agree with this. (Without respect to this particular crash.)

If GPS signal is sufficiently degraded or lost, TAWS is probably unavailable (highly dependent on what navigation system is on board). TAWS might have saved them. But needing TAWS implies loss of situational awareness.

This flight crashed in the mountains ~6 miles north of the ILS 24 approach course. At ~12 miles out on the approach course, the ILS course width is ~1 mile. A full needle deflection translates to 1/2 mile off the course. A flight is not established on the approach course with a full needle deflection. Course intercept with localizer or VOR is basic instrument work - GPS not required.

The flight requested ILS 24, later they indicated airport in sight, requested and received a clearance for a visual approach. That means pilots have full responsibility for terrain and obstruction clearance. The visual approach requirement is to maintain contact with with airport.

It seems to me they went off course, by a lot, for reasons I'm not clear on, and then descended prematurely into hostile terrain at night, which is likely why they lost visual contact with the airport. The terrain blocked their view and by the time they realized they were descending into hostile terrain they crashed.

If that's what happened, GPS signal loss is perhaps an instigating source of distraction and confusion but I do not see how it's a primary factor. If the signal becomes degraded, navigation should indicate it (auditory and visual) and that source is ignored entirely. Falling back to ground based navigation should be familiar, it doesn't need to be as precise as GPS, the instrument approach procedure has terrain clearance baked into it.

Best practice is to follow the instrument approach procedure to the final approach fix, then do the visual approach - especially at night which many have argued constitutes instrument flight conditions - mountains will be invisible. Pitch black on black.

Highly dependent on weather and the complexity of the approach. Clear skies and VFR? I would agree. Heavy weather and an instrument approach or confounding factors? Not accurate imho.

> At midnight on May 14, eight minutes after Clark and Kawsara took off from Roswell, they told Albuquerque Center that they’d lost their GPS. Unable to navigate on their own, they asked that the controller give them a heading—a magnetic direction to fly in. The controller gave them a heading to fly west, and then, a minute later, to turn north.

> The pilots said that they wanted to fly an RNAV approach to Ruidoso. This being ruled out while GPS is jammed, the King Air pilots changed their request and asked to use an alternate form of landing system called Instrument Landing System, or ILS, that doesn’t require GPS reception. At 12:05 am, the controller assured the King Air that they would provide them with vectors to guide them “in a couple of minutes.” In the meantime, they kept flying north.

> In retrospect, tragedy might have been avoided if Albuquerque air traffic control had been able to pay closer attention to the young pilots in the King Air. But tonight they were busy. Three other aircraft also reported that they’d lost their GPS and needed help. One was struggling to get a bearing on a radio beacon.

> As they turned and descended toward Ruidoso’s lights, what the pilots couldn’t see was the 10,000-foot-high mass of the Capitan Mountains lying across their path. As they drew closer, the dark mass of rock appeared to rise up, swiping away the lights of the valley. This could have created "confusion and a loss of situational awareness,” Browne says. “When those lights go out, man, you know you are in big trouble.”

Potentially low time pilots with degraded navigation aids at night (midnight) got behind the plane in an area with terrain, along with a high workload ATC not able to provide assistance more rapidly.

(disclaimer: have a private license)