A medevac flight from Roswell Air Center (ROW), New Mexico, to Sierra Blanca Regional Airport (SRR) crossed into an area where there were “GPS jamming activities” by the U.S. military — minutes later, it crashed into a mountain as it was on final approach to its destination. According to the NTSB’s Preliminary Report [PDF], the crew, alongside several other aircraft, experienced issues with their navigation system consistent with the effects of GPS jamming, as reported by Wired.
While the GPS interference seemingly did not directly cause the crash, it’s apparent that it was the first domino in a chain of events that led to the fatal accident. This raises urgent questions about GPS jamming as reported incidents of GPS interference mount across the world.
An uneventful departure
The preliminary report said that it was a dark, moonless night, meaning it would be difficult for anyone to fly visually. That’s because the dark sky and ground would make it difficult to locate the horizon and could quickly lead to spatial disorientation. The twin-engine Beechcraft King Air propeller plane took off from its base at Roswell Air Center (ROW), New Mexico, at around 11:52 pm. As it was climbing to altitude at 11:54 pm, the pilots requested and received an instrument flight rules (IFR) clearance from Albuquerque Center, the air route traffic control center in charge of the area.
This switch meant that the pilots would now primarily fly the plane using instruments in the cockpit instead of looking outside the windows. This is a normal procedure and is what most passenger airliners use during operations. Furthermore, it seems that the pilots have filed for clearance before they took off, as evidenced by their “as filed” clearance to SRR.
First sign of trouble
At around 12 midnight, Albuquerque Center told the flight crew that they were 1,000 feet above their assigned altitude. The pilots then said they were correcting their altitude, but they also mentioned that they’ve lost GPS capability. From there, they asked for a heading, and they were told to proceed to heading 275 towards SRR. About a minute after this, air traffic control (ATC) told them to proceed to heading 350 to set them up for a landing on runway 24 at SRR.
Around five minutes after this radio communication, ATC called the military and asked them to stop their GPS jamming activities in the meantime. At 12:07 am, the NTSB said that the Beechcraft’s GPS instruments resumed regular recording. The pilots then called Albuquerque Center a minute after this, saying that they had “a visual on Ruidoso,” the town nearest to SRR, and that they were transitioning to visual flight rules (VFR). This meant that they were moving away from the direct control of the ATC and would navigate and fly using visual cues.
A mountain hiding under a moonless night
As the pilots turned towards their final destination, they had a recorded altitude of 9,820 feet on their instruments. But what the pilots couldn’t see was that the Capitan Mountains, which rise to more than 10,000 feet, stood between them and SRR.
The conditions meant that there was no available illumination to light the ground. It is still unknown what happened next or what the pilots saw (or didn’t see), but the preliminary report says the last recorded information saw the plane climbing from 9,400 feet to 9,823 feet at a ground speed of 150 knots (172 mph). It impacted terrain at about 9,950 feet — some 230 feet below the Capitan Mountains Summit Radio Facility.
Visual illusion compounded by a high-stress situation
Although the weather was clear at the time of the accident, the fact that it was a dark night meant that the pilots were more susceptible to visual illusions. As the aircraft descended, they were likely using the lights of Ruidoso to guide them toward SRR.
Because they could not see that the Capitan Mountains were still between them and their destination, they likely started their descent too early. As soon as the aircraft went below the peak, they would’ve lost visual with the town, and it seemed that the pilots attempted to climb when they realized that there was a massive obstacle in front of them. Unfortunately, it seems that their efforts were too late, especially at their speeds, resulting in a controlled flight into terrain (CFIT) accident.
This was compounded by a high workload and high-stress situation. Landings and take-offs, in normal situations, are already quite hectic in the cockpit, which is why pilots practice the sterile cockpit rule, which avoids extraneous communications, at times like these. The loss of GPS signals also added to their stress, as they initially planned for an RNAV approach towards SRR. While this generally uses a combination of radio signals, it seems that their system primarily relied on GPS, which was inoperative at that time.
Aside from this, ATC also had a higher workload than usual, as they were assisting three other aircraft in the area that have been affected by the military operations. Although the military had temporarily ceased their activities, it seems that the pilots were not aware of this and elected to proceed visually instead of relying on either RNAV or the alternative instrument landing system (ILS).
We still don’t have the NTSB’s final report, so we cannot definitely say what the ultimate cause of the crash. But it seems that if the military wasn’t running a GPS jamming exercise at that time, the flight would have used RNAV from departure all the way to SRR, instead of relying on radar vectors and, ultimately, VFR.
Military activities affecting civilian flights
This isn’t the first time that military activities have been linked to a crash in the U.S in recent history. Just last year, a tragedy unfolded at Ronald Reagan Washington National Airport when a regional jet carrying 64 passengers and crew collided with an Army Black Hawk helicopter on an exercise, resulting in 67 casualties. GPS jamming is also a frequent occurrence in several hotspots in the world, like Eastern Europe, the Middle East, and even the South China Sea, which has affected airliners.
But aside from civilian airliners, many drones, especially those used for long-range attacks, also use GPS. While militaries have been developing new technologies like microwaves and lasers to shoot down these drones, one of the most cost-effective technologies that is readily available today is GPS jamming. It’s probably because of this that Russia has started putting magnetic compasses on some of their drones to help with navigation.
Even though GPS jamming might sound alarming, pilots have been flying around the world for decades, even before it came into widespread use. These include VOR (VHF Omnidirectional Range) beacons that send out signals unaffected by GPS jamming to help pilots determine where they are, ILS, which safely guides pilots towards a runway up to a certain distance, and more.
However, it seems that the sudden loss of GPS caught the pilots of the Beechcraft unaware. This, combined with the lack of visual references, a sudden change of plans from RNAV to ILS approach, and the decision to fly visually, probably led to the crash. The military’s GPS jamming exercise didn’t directly cause the crash, but it was likely the first event in the “Swiss cheese” model that ultimately caused the accident.
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