Darkness had just settled over the western horizon and NORAD had just begun tracking Santa's flight over North America.
Delta Connection Flight 3567 was headed to the Rogue Valley from Salt Lake City, about 27 miles from its destination. It was a rainy Christmas Eve, with cloud cover dropping to about 7,000 feet over the Medford airport, where the temperature was 43 degrees and visibility was 10 miles.
Family, friends and Christmas festivities awaited the 76 passengers aboard the Canadian Regional Jet, operated by a SkyWest Airlines crew, unaware danger lurked just ahead.
As it crossed the Cascades, the Bombardier CRJ-900 had dropped from 36,000 feet to 12,000 feet and slowed considerably from its 415 mph cruising speed. The plane passed from Air Traffic Control in Seattle around the time it crossed over Lakeview. About 12 minutes out, the pilot radioed Cascade Approach in Eugene (see correction, below) acknowledging it had reached a navigational fix point known as CEGAN en route to landing in Medford from the south.
"Skywest 3567, Cascade Approach, cross CEGAN at or above 7,800, cleared VOR/DME Charlie approach via the arc," the air-controller said, according to an archived transcript.
"Alright, cross CEGAN at or above 7,800 and we're cleared for the VOR/DME Charlie, Skywest 3567," the pilot responded.
Flight 3567 arced southwest behind Mount Ashland, dipping to 7,800 feet. The potentially deadly problem was that the plane — as all flights on that course — should have stayed above 10,000 feet and was in danger of smacking into one of several peaks in the Siskiyou Mountains.
Only when the Canadian Regional Jet's alarm — the Enhanced Ground Proximity Warning System — sounded did the crew realize the peril it faced.
At first there was a broken transmission from the cockpit.
"Skywest 3567, say again?" Cascade Approach responded.
"We got a terrain warning, we're climbing," the pilot said.
"Skywest 3567, roger, say intentions?" the controller asked.
"Climbing to 11, Skywest 3567," the pilot said.
During the next two minutes, Flight 3567 gained more than 3,000 feet as the pilot twisted the aircraft west, then north. By then it was too high to land at the Medford airport from the south, and the pilot requested an instrument landing from the north, swinging around the Table Rocks before touching down five minutes early.
The ensuing discussion prior to landing indicates the flight crew was perplexed.
"We received a GPS, or a, excuse me, a GPWS, which is one of our terrain warnings that comes up when we are too low," the pilot said. "We just wanted to let you... when we called you we wanted to let you know that we thought we were too low for this sector, and we wanted to confirm with you the altitude on the approach."
After asking the crew to standby, the air traffic controller responded: "Skywest 3567, what I'm showing on my approach plate is, after CEGAN, 10,000 on the arc until you're established inbound. Is that what you're showing?"
"That's what we show," the pilot said. "We were assigned an altitude of 7,800."
"Roger," Cascade Approach responded. "That altitude was at or above 7,800 until established."
"And when we were established on the arc, we were established at a lower altitude than uh... Alright, well let's get a phone number and we'll talk about it on the ground," the pilot said.
The preliminary National Transportation Safety Board report describes the incident as 27 nautical miles from the airport. Whether the pilots simply forgot the necessity of staying above 10,000 feet or the flight-chart-prescribed 10,700 elevation isn't clear. Apparently, the crew didn't immediately question Air Traffic Control's clearance for descent to 7,800-foot elevation. Flight charts show the plane shouldn't drop that low until about 14 nautical miles from the runway, with landing gear deployed about 10 miles out.
Communication mix-ups are infrequent, because both parties read back what they hear, said Michele Halleran, a former Hawaiian Airlines pilot and now a professor at Embry–Riddle Aeronautical University in Daytona Beach, Florida.
However, transmissions can go awry.
"You can have static or the radio frequency gets jumbled," Halleran said. "There are certain phrases and instructions always as a pilot you have to read back. For a pilot to read back or transmit something that's false doesn't happen that often."
When that happens, a debriefing session is in order.
"If you have a miscommunication with the controller — and that looks like what happened — I would want to follow up and discuss how things were interpreted," Halleran said. "You don't have time when you're flying."
There are multiple situations that can trigger what is known as an Aviation Safety Action Program Report, something the Federal Aviation Administration borrowed from NASA.
"If a pilot realizes there was an unintentional mistake, you file an ASAPR to protect yourself, and explain why you made the mistake," she said.
A pilot's ASAPR will often provide what they heard, what they radioed back and what they did.
"The idea of a self-report is non-punitive on the company's part, with the understanding you may get phone calls about what exactly happened to prevent something happening to other crews in the future," Halleran said. "It's actually a really good thing to do this so you have help in the sky."
Pilots might file a report after an EGPWS warning on their own accord, or because of their company's protocol.
Medford Airport Director Jerry Brienza said he received no official word of the incident.
"Human factors come into play in this industry," Brienza said. "And honestly, if it didn't happen on the airport, I wouldn't typically get a report."
SkyWest Airlines, based in St. George, Utah, didn't respond to telephone and email messages. A spokesman for the FAA in Seattle acknowledged the incident was under investigation, but provided no additional insight. NTSB investigator Andy Olvis did not respond to an email.
Even if pilots are familiar with routes and airports, conditions can change, creating challenges.
"Flying in pure daylight is different than flying at night," Halleran said.
The moon, in waxing phase, wouldn't have cast much light that evening.
There was nothing atypical or unusual about the weather on Christmas Eve, said Ryan Sandler of the National Weather Service's Medford office.
"It wasn't clear as a bell, but we hardly ever get that in December," Sandler said. "The conditions were a little better than to be expected with mid-level overcast."
Most commercial aircraft flight decks contain advanced graphics depicting terrain.
"The pilots have a moving map with a pictorial view of the ground, so they do see the mountains and altitude readings," Halleran said.
Pilots study navigation charts, altitudes and routes, terrain and approaches before departure.
"It's programmed into the airplane's electronic navigation system as well," Halleran said.
FAA regulations include built-in elevation buffers, higher in mountainous terrain, to account for meteorological and other anomalies.
"When you're close to mountains the margin is higher, typically 2,000 feet," Halleran said. "Mountains tend to disrupt air flow, so typically you have turbulence around mountains."
The EGPWS receives the aircraft's position and velocity information, then checks the position with a terrain database. The system will look ahead of the aircraft and see whether the potential for a collision with terrain exists. The system provides visual depiction of the terrain around the aircraft as yellow or red, depending on the height of the aircraft.
There is an audio element as well.
"Usually, it's an automated voice, depending on the type of warning," Halleran said. "You can program it to be female, digital or shouting. It needs to be different than a normal voice so that it's not like radio chatter in the background or your partner sitting next to you; it needs to be an attention grabber."
Most likely, she said, passengers were not aware, Halleran said. "Maybe in first class, they might have heard the warning."
— Reach reporter Greg Stiles at 541-776-4463 or firstname.lastname@example.org. Follow him on Twitter at www.twitter.com/GregMTBusiness or www.facebook.com/greg.stiles.31.
Correction: A previous version incorrectly stated pilots received the clearance to 7,800 feet over the Siskiyous from Seattle Center air traffic control. By that time, the plane had passed to Cascade Approach in Eugene.