April 2005 Volume 48 / Number 4
Landmark Accidents: Aspen Arrival
A Gulfstream III and its overbearing passenger never make the runway
It's an unfortunate aviation paradox that a strong desire to reach a destination sometimes means never getting there. Mountainous terrain and deteriorating weather always complicate arrivals, and Aspen, Colorado, is known to be challenging. Over the past decade there have been about 15 accidents with four involving fatalities at this airport. It was late March 2001 when a Gulfstream III, one of the top-line business jets, was hired to bring a party of 15 from Los Angeles to the resort area for an evening social event.
The captain and first officer reported for duty around noon Pacific Standard Time (PST) in Burbank, California. The first officer checked weather with flight service and while the forecast called for occasional IFR in low ceilings and restricted visibility with passing snow showers, there was nothing to cause major concern — other than the fact that they were flying into Aspen. The FSS specialist noted that the circling minimums for the only instrument approach were no longer authorized at night. This would play a significant role in the events to follow. An IFR flight plan was filed, with Garfield County Regional Airport in Rifle, Colorado, as the alternate. Aspen's night landing restriction required the G-III to land within 30 minutes after sunset (6:58 p.m. MST) because of noise-abatement rules.
The G-III departed Burbank at 3:38 p.m. Mountain Standard Time (MST) (2:38 p.m. PST) for the positioning flight to Los Angeles International Airport, arriving 11 minutes later. At Los Angeles, the captain and a charter department dispatcher discussed the fact that the passengers were late and discussed the weather for the flight's arrival time at Aspen-Pitkin County/Sardy Field.
Anyone who has flown charter knows that the desire to complete the mission is compelling, and top operators focus on safety first with transportation second. In this business the customer is not always right (see "Keeping the Client Happy," March Pilot). The charter client's business assistant, in a post-accident interview, mentioned that "the boss" was hosting a party in Aspen. The charter company dispatcher called the assistant at 4:30 p.m. wondering where the passengers were and advising that if the flight departed later than 4:55 p.m., it would have to divert to Rifle. The assistant located the passengers chatting in the airport parking lot.
One of the pilots mentioned the nighttime landing curfew and "the boss," upon hearing this, instructed his business assistant to call the charter company back and tell the crew to "keep their comments to themselves." When informed of the possible diversion, the boss became irate and again, through the assistant, told the charter company that the airplane was not going to be redirected. He had flown into Aspen at night before and was going to do it again.
The G-III departed Los Angeles at 5:11 p.m. MST (4:11 p.m. PST), 41 minutes late for the one-hour-35-minute flight. The estimated time of arrival at Aspen was 6:46 p.m., only 12 minutes before the landing curfew. The dispatcher recalled that during a subsequent conversation on the company frequency, the captain said the boss had pressured him to land at Aspen because "he'd spent a substantial amount of money on dinner."
At 6:37:04 p.m., the first officer called for the approach briefing. The captain answered, "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." At 6:39:56, the crew received ATIS information Hotel. Three-quarters of an hour earlier, at their originally scheduled arrival time, the 5:53 p.m. observation indicated wind from 030 degrees at 4 knots, visibility of 10 miles, scattered clouds at 2,000 feet, ceilings of 5,500 feet broken and 9,000 feet broken, temperature of 2 degrees Celsius, and a dew point of minus 3 degrees C.
Shortly afterward, a Canadair Challenger declared a missed approach. The crew was probably feeling pressured about the night curfew and the deteriorating weather. A trip to the alternate and a very unhappy client were distinct possibilities. The Gulfstream captain asked the controller if the Challenger was practicing or had actually missed the approach. The controller replied it was a real missed approach. While in descent, the flight crew discussed the location of a highway near the airport and the chance to follow it in for a visual. A quick, easy arrival by visual reference was fading with the evening twilight and the snow showers.
At 6:47:30 p.m., ATC announced that a Cessna Citation saw the airport at 10,400 feet and was making a straight-in approach. At 6:47:41, the Gulfstream captain advised 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." At 6:47:51, the first officer stated, "Could do a contact but...I don't know, probably we could not...." (A contact approach procedure allows an IFR aircraft to proceed by visual reference, with the pilot responsible for terrain avoidance. A flight must remain clear of clouds with reported ground visibility of at least one mile. Pilots must specifically request this procedure as it is used to shortcut a full instrument approach.)
At 6:48:51, the captain said, "There's the highway right there." But the first officer replied, "No, it's clouds over here on this area. I don't see it." The captain advised the flight attendant that, if the approach was not successful, they would go to Rifle because "it's too late in the evening...." Shortly after this a passenger was allowed to sit in the jump seat to observe the approach. At 6:53:09 another Canadair Challenger missed the approach, to which the first officer remarked, "That's...not...good."
At 6:56:06 p.m. the flight was cleared for the VOR/DME-C approach. (Page 90 shows the current Aspen instrument approach chart.) A few seconds later ATC reported that the visibility north of the airport was two miles (at minimums). The approach controller then switched the G-III over to Tower frequency. The Tower advised that the Gulfstream was following another Challenger, whose crew subsequently reported a missed approach at 6:58:00.
At 6:58:13, the jump-seat observer asked, "Are we clear?" The captain replied, "Not yet. The guy in front of us didn't make it either." There was some discussion with the crew about the approach step-down fixes, and at 7:00:08, the jump-seat observer said, "Snow." At 7:00:22, with the aircraft at 10,400 feet, 200 feet above minimums, the captain declared, "OK...I'm breaking out," and asked the Tower about 5 seconds later whether the runway lights were all the way up. The controller responded that they were on high. Eight seconds later the first officer said, "OK, you can go...10,200 [the minimum descent altitude]."
At 7:00:43 p.m., there was more discussion about seeing the runway and then the Tower called to ask if the G-III had the runway in sight. The G-III was passing through 10,000 feet. The first officer advised the controller that the runway was in sight. At 7:01:13, the first officer stated, "To the right is good." According to radar data, the airport was to the left of the airplane at this time.
At 7:01:21, the airplane's configuration alarm sounded, noting that something was not set properly. This is not unusual and reminds the crew to make the necessary adjustments. At 7:01:31 and 7:01:34, the cockpit voice recorder (CVR) captured the sound of the aircraft's 900- and 800-foot call-outs, respectively. The flight profile advisory (FPA) unit continued 700- and 600-foot call-outs and at 7:01:42, the first officer stated, "To the right," which the captain repeated about one second later. Radar data indicated that the airport was still to the left of the G-III.
Three seconds later the ground proximity warning system (GPWS) sounded, indicating the flight was getting very close to terrain. Radar data showed the airplane started a left turn at 7:01:47 and two seconds later the GPWS announced a sink rate alert. This indicated that the flight path with a high rate of descent was not stabilized. At 7:01:52 there was another GPWS sink rate alert and the FPA 400-foot call-out. One second later the engines went to maximum power. The FPA 200-foot call-out and a GPWS warning of steep bank angle occurred almost simultaneously.
The G-III crashed into terrain at 7:01:58 in a steep left bank about 2,400 feet short of the Runway 15 threshold, 300 feet to the right (west) of the runway centerline and 100 feet above the runway threshold elevation. It was 34 minutes after official sunset. Post-crash analysis estimated that the G-III impacted at a 49-degree left-wing-down attitude, with a flight-path angle of minus 15 degrees. There were 18 fatalities: two crewmembers, a flight attendant, and 15 passengers.
The automated surface observation system (ASOS) transmitted a special report at 7:12:26 p.m. (10 and one-half minutes after the accident) showing visibility down to one and three-quarter miles in light snow. Eight minutes later, the visibility had increased to three miles in light snow and mist. The ASOS five-minute observations surrounding the time of the accident (7:00:31 and 7:05:31) indicated that the visibility was nine and six miles in light snow, respectively. The ASOS one-minute visibility value about the time of the accident was eight miles. Weather observations at the alternate airport at Rifle indicated light winds, clear skies below 12,000 feet, and 10-mile visibility.
ASOS observations use an averaging algorithm and thus will not instantaneously reflect rapidly changing ceiling or visibility values. Obviously, the weather observations at the site, whether human or automated, may be quite different from what a pilot may see on an instrument approach a mile or two away. The augmented observation reported to the crew by ATC, of two miles' visibility north, was reasonably accurate for operational purposes.
The captain was type rated in the Gulfstream III in January 1990 and had accumulated 9,900 hours' total flying time, including 7,900 hours as pilot in command and 1,475 hours in the G-III. The first officer received his initial G-III type rating on February 9, 2001, and had accumulated 5,500 hours' total flying time, including 4,612 hours as pilot in command and 913 hours in the G-II and -III (110 of which were with the charter operator as a G-III second in command). According to family members, both pilots had slept about eight hours the night before the accident. Charter operation records showed the captain had been paired with the first officer for five months, and they had flown to Aspen twice before during daylight.
The pilots were trained in accordance with the company manual, which included initial qualification followed by annual recurrent simulator training in the G-III. Part of that training included instrument approach procedures, crew coordination on the approach, and a controlled flight into terrain (CFIT) training module. CFIT hazards, enhancement of situational awareness, recognition and evaluation of potential dangers, and a simulator profile that includes a ground-proximity escape maneuver are part of the training.
The accident airplane was manufactured in 1980 and was equipped with an FPA unit, which announces radio altitudes every 100 feet between 100 and 1,000 feet above the ground and deviations from a selected altitude. The airplane was also equipped with GPWS avionics that announce the 500- and 200-foot radar altitude call-outs and alerts for excessive descent rate, excessive closure rate to terrain, insufficient terrain clearance, and excessive bank angle. The CVR indicated that the FPA and the GPWS provided overlapping call-outs at the 500- and 200-foot altitudes. According to the NTSB, the aircraft was maintained, loaded, and fueled properly.
The airport and approach
Aspen's airport is at an elevation of 7,815 feet msl and is surrounded on all sides by high terrain. There is only one runway, 15/33.
The VOR/DME-C instrument approach does not include straight-in minimums because of excessive descent gradients. The terminal instrument procedures (TERPS) require that the maximum gradient for straight-in minimums between the final-approach-fix minimum altitude and the runway-threshold-crossing height cannot exceed 400 feet per mile. The descent gradient between ALLIX and the threshold-crossing height of Runway 15 is 700 feet per mile, hence the high circling minimums. Pilots are not required to circle provided they have the runway visually and have adequate time and altitude to make a normal landing.
Less than 10 days before the accident an FAA flight inspection crew working on a proposed GPS approach procedure to Runway 15 recommended that circling not be allowed at night and a notam was issued stating, "Circling NA [not authorized] at night" at Aspen. Since no straight-in minimums were published for the VOR/DME approach, the entire procedure was not authorized at night, but the wording may not have been entirely clear.
The notam was given to the FSS and included in the first officer's preflight briefing but not forwarded to the Aspen Tower as required. The approach never should have been authorized in the first place.
Air traffic control tower information
The Aspen controllers closely monitor the progress of airplanes executing the VOR/DME-C approach. The controllers pay close attention to minimum step-down fix altitudes and advise pilots immediately when they see an aircraft below a minimum altitude. During a post-accident interview, the Tower controller noted that she saw the G-III descend on radar below a step-down altitude but was unable to see the aircraft visually, although the crew called the runway in sight. It was at this time that she asked the crew if they had the runway in sight. When the G-III appeared about a minute later, it was pointed at Shale Bluffs (located northwest of the runway). From the Tower it appeared to be accelerating and was rolling rapidly to its left. The controller anticipated the crash and reached for the crash phone.
According to radar analysis, the G-III was not stabilized in the final approach and after passing ALLIX, it descended in excess of 2,000 feet per minute with an airspeed of about 125 knots (the reference airspeed for landing was 123 knots). It leveled momentarily at 10,000 feet for about 10 seconds and descended again at 2,200 feet per minute, hence the sink rate warning from the GPWS.
Post-accident analysis revealed that landing flaps and gear were down in addition to the wing spoilers being deployed. This is contrary to the G-III flight manual, which does not allow spoiler use with either landing flaps or gear extended. The pilot's intent appears to have been to bring the aircraft below the snow showers and gain visual contact while not allowing the speed to increase. This improper configuration likely contributed to the very high sink rates.
As always, there are multiple factors at work in this tragedy. Obviously, descending below landing minimums without a clear view of the runway or its environment is not a life-prolonging activity. This crew was committed to land despite all evidence that advised against it. Pressure from the charter customer contributed heavily to that mindset. Having a passenger in the jump seat and not adhering to a sterile cockpit rule (no irrelevant conversation below a predetermined altitude) were also distractions.
Additionally, the FAA failed to write the notam prohibiting night approaches clearly and transmit it to Aspen Tower. Both those oversights were corrected immediately after the accident.
FAR Part 91 flights don't have the same external pressures that charter flights do, but in some respects the decisions involved may be tougher. When we decide not to fly or decide to divert, we're saying no to family, friends, and ourselves. Regardless of which set of rules we operate under, balancing the risk-and-reward equation correctly is impossible if we rationalize away the risk. Dozens of pilots, in all sizes of aircraft, make the wrong choices every year, trying deliberately or inadvertently to get just a little more utility out of their aircraft for themselves or their employers. As pilot in command, tough love means occasionally having to say you're sorry.
Bruce Landsberg is the executive director of the AOPA Air Safety Foundation.