ASPEN AIRPORT (ASE, also known as Sardy Field) is known among pilots as one of the most challenging approaches in the US. The single runway is at an elevation of 7,820 feet (2,383 metres) and surrounded by mountains. The minimum decision altitude (MDA) is 10,200 feet and incoming aircraft must make staggered steep descents to safely reach the threshold.

On the 29th of March in 2001 a private jet, a Gulfstream III, crashed into sloping terrain on final approach, killing three crew members and fifteen passengers on impact.

This post is excerpted from Why Planes Crash Casefiles: 2001

The Captain and the First Officer were both properly certificated and qualified with thousands of hours of experience. Neither was fatigued. The aircraft was properly certified and equipped. The navigational aids and airport lighting systems were all functioning as intended.

And yet the $10 million Gulfstream jet crashed 2,400 feet (730 metres) short of the runway threshold, killing all the occupants.

On the morning of Thursday the 29th, the Captain and his First Officer arrived at Burbank airport around lunchtime for a charter flight taking fifteen passengers to a dinner party in Aspen. Note: All times are given in Mountain Standard Time, which was the local time in Aspen.

As a part of the pre-flight planning, the First Officer discovered that the approach procedure at Aspen had been updated two days previous. On the 27th of March, two days before the flight, the FAA had released a Notice to Airmen (NOTAM) stating that circling was not authorised at night, as the FAA had concluded that instrument approaches into the airfield in the dark were dangerous. There is no straight-in approach to Aspen. The high terrain on all sides means that the glide slope would be too steep for a stable approach in instrument conditions.

The Captain expected a visual approach and stated early on that they would only try the approach once. If they weren’t able to get in on the first attempt, they would divert to their alternate airport in Rifle, Colorado. The Gulfstream departed Burbank with three crew at 15:38 for the eleven-minute flight to Los Angeles International where they planned to pick up their passengers and take them to Aspen. However, the passengers were late.

While waiting at LAX, the Captain discussed Aspen’s nighttime landing restriction with another pilot and the First Officer. Aspen ASE required aircraft to land “no later than 30 minutes after sunset” to comply with local noise restriction legislation. Sunset on the 29th was at 18:28, so the aircraft needed to land by 18:58 to comply with the restriction. It’s not known whether the First Officer mentioned the NOTAM; however it is clear that the flight crew planned be on the ground before night fell.

The Gulfstream eventually departed at 17:11, forty-one minutes later than the First Officer had scheduled. The flight was expected to be one hour thirty-five minutes, for an estimated arrival at 18:46: twelve minutes before the curfew. The Cockpit Voice Recorder recovered from the accident makes it clear that the flight crew were keeping tabs on the time.

18:37:04 The First Officer calls for an approach briefing. The Captain responds, “We’re . . . probably gonna make it a visual . . . if we don’t get the airport over here we’ll go ahead and shoot that approach . . . We’re not going to have a bunch of extra gas so we only get to shoot it once and then we’re going to Rifle.”

18:44:22 The Gulfstream changes frequency to ASE Approach Control and makes contact with the controller.

18:44:43 A Canadair Challenger 600 contacts the controller to request another approach. The approach controller clears the aircraft to continue on the missed approach procedure.

18:45:00 First Officer states, “I hope he’s doing practice approaches.”

A missed approach is initiated when the approach is unstabilised or unsafe and cannot be completed to landing. The approach plates for an airport include a decision height or missed approach point, by which time the runway must be in sight. If it isn’t in sight by that point, or there is any other reason that a safe landing might not be possible, the missed approach procedure is initiated. The aircraft will climb away on a specific heading and, once the procedure is completed, can initiate another approach attempt at the same airport or divert to an alternate airport, depending on the conditions and reasons for the missed approach.

A missed approach is a demanding situation and often pilots will deliberately request the missed approach procedure as a part of their training. This was what the First Officer was hoping for, because if it wasn’t a practice missed approach, then it was likely that visibility at the airport was uncomfortably close to minimums.

At the time, the cloud tops were at 16,000 feet and the aircraft was in and out of cloud after descending past this level.

About 3 seconds later, the captain asked the controller whether the pilot of N527JA was practicing or had actually missed the approach. The controller replied that the pilot had missed the approach and indicated that he had seen the airplane at 10,400 feet. The controller also informed the captain that two other airplanes were on approach to ASE.

—From the official report

18:45:45 The Captain says, “Where’s that . . . highway? Can we get down in there?”

18:45:56 The Captain asks, “Can you see?” The First Officer replies with, “I’m looking, I’m looking. . . .  no.”

18:46:26 The Captain says, “I got it,” followed by “Can’t really see up there, can ya?” The First Officer replied with “Nope, not really. I see a river but I don’t see anything else.”

18:47:19 The First Officer says, “I see . . . some towns over here and the highway’s leading that way but I’m not sure.”

18:47:30 The Approach controller makes a general broadcast that the pilot of a Cessna Citation saw the airport at 10,400 feet, 200 feet above the minimum decision altitude, and was making a straight-in approach. The First Officer says, “Ah, that’s good.”

18:47:41 The Captain tells the controller, “I can almost see up the canyon from here but I don’t know the terrain well enough or I’d take the visual.”

Aspen has a VHF omnidirectional range / distance measuring equipment (VOR/DME) instrument approach which does not include straight-in minimums because the descent would be too steep. The instrument approach is a non-precision approach. After you pass the Red Table VOR (the initial approach fix), you reduce your altitude at specific intervals (called step-downs), which ensure that you are clear of the terrain. As you approach the airfield, you should have the runway (and surrounding terrain) in sight and be able to finish your approach visually.

These “step-downs” are staggered descents based on your DME distance. Reducing your altitude in steps ensures that you remain at a safe altitude as you approach the runway.

As you calibrate your height based on your distance from the runway, you can continue the descent to the minimum decision altitude (MDA) for the non-precision approach. At Aspen, the MDA for the non-precision approach is 10,200 feet. Once you reach this altitude, you must stop your descent unless you have the runway in sight and can continue the landing visually. You can continue your approach at (but not below) the minimum decision altitude until you reach the missed approach point, which is a specific distance, by DME, from the runway. If you cannot see the runway once you have reached the missed approach point, you must break off the approach and climb away.

18:48:04 The First Officer says, “Remember that crazy guy in this Lear[jet] when we were . . . on the ground in Aspen last time and he [stated that he could] see the airport but he couldn’t see it.” The Captain doesn’t respond.

The visual approach into Aspen follows parallel to a highway which can be seen from the distance, clearly visible in the above aerial photograph.

18:48:51 The Captain says, “There’s the highway right there.”

18:49:28 The Captain asks the First Officer if he can see the highway. The First Officer can’t. “No, it’s clouds over here on this area I don’t see it.” The Captain responds with, “But it’s right there.”

18:49:34 The Captain then says, “Oh, I mean, we’ll shoot it from here, I mean we’re here but we only get to do it once.” He commented again that if the approach was not successful, they would need to divert to Rifle as it was too late in the evening to try again.

He doesn’t seem confident that he has the highway in sight, let alone the airport. However, he did not brief the missed approach procedure, which meant that the crew weren’t prepared for a missed approach even though it was seeming more and more likely that visibility was too low.

18:53:57 The flight attendant asks whether a male passenger can come into the cockpit and sit in the jumpseat. The cockpit voice recorder records the flight attendant asking a passenger to ensure his seatbelt is on, followed by the clunk of a seatbelt buckle being closed.

18:55:05 The Canadair Challenger 600 transmits his intention to execute another missed approach. The Captain comments, “The weather’s gone down, they’re not making it in.” An unidentified male voice in the cockpit responds with, “Oh, really.”

Flight crew members can’t engage in “any activity which could distract them from their duties” including non-essential conversation once the aircraft has descended below 10,000 feet msl. However the Gulfstream was above that altitude when the passenger came forward.

18:56:06 The Approach controller clears the flight crew for the VOR/DME approach and instructs them to cross the VOR at or above an altitude of 14,000 feet. The flight is five miles from the Red Table VOR, which is the initial approach fix.

18:56:23 The First Officer says, “After the VOR, you are cleared to twelve thousand seven hundred.”

18:58:00 The Approach controller asks the Canadair Challenger 600 whether he had the airport in sight, to which he replied, “Negative, going around.”

18:58:13 The unidentified male voice in the cockpit says, “Are we clear?” The Captain replies, “Not yet. The guy in front of us didn’t make it either.” He asks the First Officer for the next step-down altitude and the First Officer responds with the information.

For this segment of the approach, they needed to maintain 12,200 feet until they passed a point known as ALLIX, which is 6 DME (6 miles south of the Red Table VOR by DME), at which point they can descend to 10,400 feet. They actually passed ALLIX at 12,100 feet, 100 feet below the minimum specified altitude for that step.

18:59:30 The Captain calls for the landing gear and landing flaps. The First Officer states that the step-down fix at 10,400 feet is 9.5 DME (9.5 miles south of the Red Table VOR). He calls Three Greens (confirming that the nose and main wheels are down) and then that the missed approach point is 11 DME (1.5 miles further).

The missed approach point is the point at which they were required to break off the approach and follow the missed approach procedure unless they had the runway in sight.

19:00:08 The unidentified male voice says, “Snow.”

The aircraft was at 10,400 feet and about 4.4 miles north of the airport. The Captain said, “Okay, I’m breaking out,” the first clear statement that he could see the ground. However, about 5 seconds later, he asked the Approach controller whether the runway lights were all the way up. The controller said, “Affirmative, they are on high.”

19:00:43 The Captain asks the First Officer whether he can see the runway. The First Officer’s response is unintelligible.

The aircraft has been descending at about 2,200 feet per minute but then levelled off at 10,100 feet, about 300 feet below the specified altitude for the step-down and also below the 10,200 foot minimum descent altitude, without any indication that the runway was in sight for either of the flight crew. The Captain neither corrected the descent nor initiated a missed approach. The First Officer did not challenge the Captain. The Captain asked if he could see the highway and the First Officer said, “see highway,” but it wasn’t clear if this was a statement or a simple repetition.

The descent continued about 10 seconds later. The Approach controller noticed that they have descended past the step-down altitude and the minimum decision height and asks them if they have the runway in sight. Within the cockpit, the First Officer said “Affirmative,” and the Captain said, “Yes, now we do.” The First Officer confirmed to the controller that the runway was in sight. At this point, they were at an altitude of 9,750 feet.

19:01:13 The First Officer says, “. . . to the right is good” and the aircraft turns slightly to the right as they continue their descent. They are now 900 feet below the minimum altitude. The First Officer should be monitoring the altitude and calling out the altitude deviation as they descend, but he says nothing about the altitude.

According to the radar data taken after the fact, the airport was actually to the left of the aircraft at that moment. The descent continued at a rate of 2,200 feet per minute.

19:01:21 A configuration alarm sounds to indicate that the spoilers have been deployed after the aircraft is configured for landing. The engine power is reduced at the same time, which will increase the aircraft’s rate of descent. The Captain likely is still trying to get under the snow showers so he can see, but on the Gulfstream the spoilers shouldn’t be extended when the aircraft is configured for landing, and the lower power setting does not meet the minimum power required for going around.

19:01:28 The Flight Profile Advisory unit announces 1,000 feet, their current height above the ground. The First Officer calls out, “one thousand to go.” Over the next few seconds, the unit announces 900 and 800 feet callouts.

19:01:36 The Gulfstream passes the missed approach point at an altitude of 8,300 feet, 485 feet above the airfield elevation, rather than the specified 2,385 feet above the field that it should be.

The First Officer should have called out that they had reached the missed approach point and whether the runway was in sight. The Captain should have announced his intentions. Instead, as they passed through the missed approach point, the Captain said, “Where’s it at?”

The Flight Profile Advisory continued its count down: 700 feet, 600 feet. They were below the minimum descent altitude, past the missed approach point, close to the ground, in mountainous terrain. It was insane to continue.

19:01:42 The First Officer says, “To the right.” The Captain repeats his words. The aircraft continues to bank gently to the right. The aircraft is flying over a low valley so the Flight Profile Advisory does not call out 500 feet. The terrain dropped over 700 feet lower than airport elevation and then rose again as the Gulfstream continued its ill-considered descent.

The radar data is clear: the runway was still to the left of the aircraft.

19:01:47 The aircraft stops turning to the right and begins a turn to the left. This is the first clear indication that the Captain had seen the airport.

The local controller saw the Gulfstream for the first time as it emerged from a snow shower and banked steeply to the left. It was west of the runway and at low altitude. She immediately reached for the crash phone.

19:01:49 The Ground Proximity Warning System sounds: SINK RATE, SINK RATE. The Flight Profile Advisory calls out 400 feet. The Gulfstream is banking to the left at 10º and the bank angle is increasing.

19:01:52 The engines are increased to maximum power. The Flight Profile Advisory unit calls out 300 feet. The Ground Proximity Warning System and Flight Profile Advisory unit both sound alerts at 200 feet above ground level.

19:01:57 A few seconds later, the Ground Proximity Warning System sounds the bank angle alert: the aircraft is banked about 40º, left wing down. Then the Cockpit Voice Recorder data ends.

The Gulfstream crashed into terrain 2,400 feet short of the runway 15 threshold, 300 feet to the right (west) of the runway centre-line and, at the point of impact, 100 feet above the runway threshold elevation. A 72-foot ground scar showed that the left wing touched the ground first, with the aircraft in a 49º left-wing-down attitude. The aircraft crushed up like an accordion. The three flight crew and fifteen passengers all died on impact from massive blunt force trauma.

On the surface, the cause is clear. The flight crew persisted in an unsafe approach in bad weather in mountainous terrain long after they should have turned back. However, as far as the FAA was concerned, Aspen was closed at night. A critical issue for the investigation was why the aircraft was cleared for the approach in the first place.

The problem came back to the Notice to Airmen (NOTAM) that had been released two days previously. A recent flight inspection led the FAA to decide that the areas of unlighted terrain could conflict with traffic patterns and thus it was unsafe to allow an instrument approach procedure at night. However the NOTAM stated that circling was not authorised at night, which was meant to imply that the instrument procedure was not allowed at night, as there are no straight-in minimums published for Aspen. With this vague wording, however, the First Officer may have understood that an approach was still authorised so long as no circle to land manoeuvre was done. Worse, the controllers at Aspen had not seen the NOTAM at all. As a result of human error, the Denver Center had never sent a copy to Aspen. The controller should have notified the flight crew about the NOTAM and it should have been included on the ATIS (recorded airfield and weather information) that the flight crew had listened to shortly before their approach. The controller did warn all aircraft on frequency that the visibility had dropped to 2 miles but he did not know about the NOTAM.

On top of this, night was early. The crash took place 34 minutes after official sunset, 7 minutes after the beginning of official night. However, in mountainous terrain, darkness doesn’t watch the clock. The Safety Board calculated that the sun had set below the mountainous terrain about 25 minutes before the “official sunset”, with civil twilight ending around 18:30 rather than 18:55. In addition, a dark shadow from a westerly ridge crossed the accident 79 minutes earlier than the official sunset. A controller commented that it was “very dark” previous to the accident.

Those issues are all safety nets. None of these issues explain why the flight crew continued this ill-fated approach in borderline conditions as night fell.

The flight crew were both experienced pilots who knew the local terrain and had done CRM/human factors training. Yet they continued on below the minimum decision height and past the missed approach point, despite the snowstorms and rapid darkness that blocked their view of the mountains surrounding the airfield.

The crew coordination wasn’t brilliant. The First Officer did not keep up with the callouts required on an instrument approach. The Captain didn’t go over the instrument approach procedure and more importantly didn’t go over the missed approach procedure, even when he was aware that the aircraft in front of him were having to execute it. Perceived pressure to land is generally associated with inexperienced pilots who manage to convince themselves that they must land the plane at all costs. And yet, they’d started the flight in clear agreement that they would attempt to get into Aspen once and if it wasn’t visual, they would divert to Rifle. So why did they suddenly fixate on getting into Aspen at all costs?

Initially, the Captain and his first officer discussed the location of the runway and the highway, both clear that they do not have it in sight. In retrospect, the First Officer’s comment is chilling: “Remember that crazy guy in this Lear[jet] when we were . . . on the ground in Aspen last time and he [stated that he could] see the airport but he couldn’t see it.”

A few minutes later, a passenger enters the cockpit and sits in the jumpseat. From this point on, there is no active discussion about how difficult it is to see the airfield, other than the Captain asking the controller if the runway lights were turned all the way up. They pass the missed approach and the minimum decision altitude and there is no evidence that they have visual contact with the runway. The controller noticed that they had descended past the step-down altitude and asked if they had the runway in sight. The two flight crew agree that they do, without any discussion as to what they’ve seen (the lights, the highway, or any other visual reference point). Neither crew member said anything about seeing the runway until directly asked, at which point they agreed in unison that it was there. The controller reported later that she could not see the aircraft when the First Officer reported that they had the runway in sight. Most damning, however, is that the aircraft turned to the right, when a left turn was required to align with the runway.

It’s not clear whether the jumpseat passenger was the client or one of his guests. The client had chartered the jet to take his guests to a party he was hosting in Aspen. The cascade of events that led to the crash actually started that afternoon when the flight crew arrived at Los Angeles International Airport but could not find the passengers. At 16:30, the charter company phoned the client’s business assistant to say that the passengers weren’t there. During that conversation, the business assistant was told that the latest time that the aircraft could depart was 16:55.

The business assistant discovered that all but two of the passengers were in the airport parking lot. The two missing passengers included his employer, the client. The flight crew collected the passengers who had arrived and boarded them onto the plane, explaining that if the other two did not arrive shortly, they would be too late to be able to land at Aspen. One of the passengers relayed this conversation to the client. The client told his business assistant to call the charter company and relay a message to the pilot that he should “keep his comments to himself.”

The business assistant told his employer that the flight might have to be diverted to Rifle and said that his employer became irate. The business assistant said that his employer told him to call the charter company and tell them that the airplane was not to be diverted. The employer told the business assistant to tell the charter company that he’d flown into Aspen at night before and he was going to do it again. The business assistant stated that he then contacted the charter company to express his employer’s displeasure about the possibility of not landing at Aspen.

The Gulfstream departed Los Angeles Airport at 17:11, forty-one minutes later than scheduled and 15 minutes past the latest time for departure given to the client. At 18:30, the Captain spoke to the scheduler at the charter company and told the scheduler that it was important that they land at Aspen because “the customer spent a substantial amount of money on dinner.”

That conversation was just half an hour before the crash.

The National Transportation Safety Board determines that the probable cause of this accident was the flight crew’s operation of the airplane below the minimum descent altitude without an appropriate visual reference for the runway.

Contributing to the cause of the accident were the Federal Aviation Administration’s (FAA) unclear wording of the March 27, 2001, Notice to Airmen regarding the nighttime restriction for the VOR/DME-C approach to the airport and the FAA’s failure to communicate this restriction to the Aspen tower; the inability of the flight crew to adequately see the mountainous terrain because of the darkness and the weather conditions; and the pressure on the captain to land from the charter customer and because of the airplane’s delayed departure and the airport’s nighttime landing restriction.

The day after the accident, the FAA issued a revised NOTAM from “circling not authorised at night” to “procedure not available at night”. Within the next fortnight, the charter company distributed a memorandum to state that airport operations at Aspen and three other airports were prohibited between sunset and sunrise. The memorandum stated:

…if you cannot accomplish a landing and be on the ground at one of these airports before sunset you must divert to a suitable alternate. All passengers for one of these destinations must be informed of this policy. Flight crew members must report any violation of this policy or pressure from passengers to violate this policy to the Director of Operations or Chief Pilot.

New internal regulations were also put into place that only crew members, check airmen or FAA observers could use the jump seat. Under no circumstances are passengers allowed to move forward.

In the end, the poor cockpit resource management in the final minutes of the flight is the critical factor. The flight crew were staring out the window searching for the runway, rather than focusing on the flight. The Captain continued to descend past the minimum decision altitude in hopes of locating the airfield and the First Officer did not challenge the Captain’s actions nor call out the altitude as they descended into mountainous terrain.

However, understanding the contributing factors are what helps us to keep this from happening again. The FAA had already determined that night flight into Aspen was dangerous but the NOTAM was ambiguous and did not make the issue clear. The pressure from the client on the other hand, was clear and unambiguous: if the Gulfstream did not make it into Aspen, he was going to be very unhappy. Three other missed approaches were reported on the frequency and the weather was snowy and dark. Long after the Captain should have abandoned the approach, he continued to search for the runway, knowing he had only one chance to get into Aspen. The presence of the passenger in the jumpseat, especially if it was the charter client, could only have increased the pressure to get in. Rather than accept that they were going to have to abandon the approach and divert to Rifle, he and his First Officer kept trying to spot the runway, desperately attempting to come in safely after dark at one of the most demanding airport approaches in the country.

Traditionally, pilots are seen as confident and courageous. This tragic evening, the Captain was challenged to perform and he did his best to deliver, despite the adverse conditions. In modern aviation, we are finally acknowledging that cautious good judgement is a much more useful trait in pilots than confidence and courage.

• Original accident report:
  http://https://www.ntsb.gov/investigations/Pages/DCA01MA034.aspx

Originally published in Why Planes Crash Casefiles: 2001