Situational Unawareness

Word came at 9:55 P.M. to the Chinle, Arizona, office of an air ambulance service that a patient needed transport from Alamosa, Colorado, 192 nm
to the east-northeast. Forty minutes later, a King Air C90 with a pilot, a paramedic and a nurse aboard was airborne. It never arrived. The airplane struck a ridge 37 nm west of Alamosa; all three occupants died.

The outlook called for scattered clouds at 8,000 to 10,000 feet agl, a broken layer at 12,000 to 14,000, widely scattered light rain showers and isolated thunderstorms, with no warnings for mountain obscuration.

The 46-year-old ATP made a couple of careless mistakes at the start of the flight. He identified himself to Denver Center with the callsign of one of the company’s other King Airs, and he told his dispatcher, a minute after getting airborne, that his time en route would be 20 minutes.

Checking in with Denver for VFR flight following, as company rules required, the pilot first climbed to 13,500, then descended to 11,500, then climbed back up to 13,500. The terrain elevation over the first half of the route, across the high desert of northern Arizona and New Mexico, is around 6,000 feet; it is unlighted except for widely scattered towns and a few lightly traveled roads. The moon had set hours earlier, and the darkness was almost complete.

Forty minutes into the flight, Denver Center gave the pilot a frequency change. Coming up on the new frequency, the pilot reported that he was “on the descent into Alamosa.” The controller gave him the altimeter setting. The pilot then asked for “the minimum vectoring altitude out here.” The controller asked him to repeat the request. “What is the MSA [minimum safe altitude] out here, do you know?”

The controller still did not understand. “I guess I’m just not understanding what you’re saying,” he said. “Either I’m really tired ... you’re talking a little fast; slow her down for me a little, will ya?”

“I’m actually new into Alamosa,” the pilot replied. “Just wondering what the minimum descent altitude was out here.”

The controller, finally understanding the pilot’s confusingly worded request — minimum safe altitude, minimum vectoring altitude and minimum descent altitude are three different things — told him that the MIA (minimum IFR altitude) for the area he was in was 15,000 feet. He added that he would be “cutting across the corner” of an area where the MIA was slightly higher — 15,300 feet — before it started to drop toward Alamosa, where the field elevation is 7,539 feet. After explaining that the flight would be passing through four different MIA areas, the controller told the pilot that he was now “getting ready to enter the 15,300 minimum IFR altitude area.” The pilot acknowledged and, at around this time, began to descend from 13,500 feet. The last radar hit, a minute and nine seconds later, reported a Mode C altitude of 11,700 feet. An instant after that, the King Air struck an 11,930-foot ridge, sliding uphill as it disintegrated and caught fire. The 900-foot debris path ended just below the crest of the ridge.

The NTSB found the probable cause to have been, somewhat tautologically, “the pilot’s failure to maintain clearance from mountainous terrain.” Contributing factors were “inadequate preflight planning, improper in-flight planning and decision-making, the dark night, and the controller’s failure to issue a safety alert to the pilot.”

Regarding the role of the controller, the Safety Board noted that he “was aware of the airplane’s position, altitude, general route of flight and its proximity to terrain” and had a duty to immediately issue an alert to the pilot if he believed that the aircraft’s altitude placed it “in an unsafe proximity to terrain [or] obstructions.” It seems probable, however, that the controller, having laid out the minimum instrument altitude information to the pilot in detail, and knowing that he was VFR, felt that he had fulfilled the spirit of the requirement.

There were some indications, from both infrared satellite imagery and weather observations at a point close to the accident site, that orographic fog or heavy haze may have existed over the ridge, which lay athwart the generally westerly flow. The board observed, without making an explicit connection, that the pilot was under investigation by the FAA for having, during a charter flight, flown into cloud — four times, two of them for more than five minutes — without a clearance.

This had occurred before he was hired by the air ambulance service — where he had worked for only two months — and he had not reported the pending “certificate action” on his application.

The airplane was equipped with a cockpit voice recorder and with an altitude alert unit that sounded a warning tone when the airplane approached a preset altitude. (Because it had fewer than six passenger seats, the King Air was not subject to the Part 135 TAWS requirements.) Thirty-five seconds before the crash, the CVR recorded a tone from the altitude alert unit, followed by the pilot’s voice saying “Let’s go climb.”

Despite telling the controller that he was “new into Alamosa,” the pilot had in fact been there during his training and again on a night flight just two weeks earlier.

But, as his initial estimate of 20 minutes for the flight from Chinle to Alamosa suggested, he may have been vague about the geography. The essential thing to have known was that 40 nm west of Alamosa a ridge rose a mile above the surrounding terrain. A 12,778-foot mountain poked up into the airway, Victor 210, between Farmington and Alamosa, and a 13,300-foot peak rose a little to the north of it. It would be apparent from a glance at a VFR chart that on a dark night you could not safely descend below 13,500 feet until you were within 30 nm of Alamosa.

What did the pilot know? In VFR conditions, when you are over mountains and approaching a lighted area at a lower elevation, you see the silhouette of the mountains eclipsing some of the lights. If lights appear to rise from behind the silhouette, you will clear the obstacle; if they appear to sink beneath it, you are on the way to a collision with terrain. Your aim point should be well above the ridge to ensure reasonable clearance. If a ridge is covered by clouds, it may be difficult to be sure what is happening; lights may appear and disappear haphazardly as your position shifts with respect to the obscuration.

Terrain awareness and warning systems (TAWS) are intended to deal with this sort of situation; so are synthetic and infrared-enhanced vision. But most airplanes do not have them.

The NTSB’s report implies, but does not assert, that the pilot may have flown into cloud, most likely inadvertently, over the final ridge. His asking the controller for the MIA, and his saying “Let’s go climb” in response to the altitude alert warning, suggest that he was uncertain of his position with respect to the local terrain, did not have visual contact with the lights of Alamosa and did not have a chart open in front of him. An IFR en route chart would have supplied the information he was asking the controller for, and a VFR chart would have made the danger of prematurely descending below 13,500 feet quite obvious.

The NTSB’s mention of “inadequate preflight planning” goes to the crux of this accident. The narrative of the flight, beginning with the estimate of the time en route as 20 minutes, suggests a certain hasty carelessness and an assumption that the pilot could make it up as he went along. In principle, he was right: A flight over mountainous terrain in total darkness should not present any difficulty to a pressurized twin turboprop. But it would require being aware of the salient characteristics of the route; climbing to an altitude that ensured ample terrain clearance; remaining at altitude until definitely clear of obstacles; and monitoring position, altitude and terrain. You have to be sure about these things; you may be penalized for guessing.

This article is based on the NTSB’s report of the accident and is intended to bring the issues raised to our readers’ attention. It is not intended to judge or to reach any definitive conclusions about the ability or capacity of any person, living or dead, or any aircraft or accessory.

Peter Garrison taught himself to use a slide rule and tin snips, built an airplane in his backyard, and flew it to Japan. He began contributing to FLYING in 1968, and he continues to share his columns, "Technicalities" and "Aftermath," with FLYING readers.

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