Aspen, CO, USA
N500SW
LEARJET INC 60
While the first officer was flying the airplane on a visual approach to the airport located in a steep mountain valley, the tower controller informed him that the pilot of a Citation that had landed about 10 minutes earlier had reported low-level windshear with a 15-knot loss of airspeed on short final. The first officer used the spoilers while on the left base leg and then maneuvered the airplane in an "S-turn" on the final leg to correct for a too-steep approach. Just as the airplane was about to touch down with the airspeed decreasing, the captain made several calls for "power" and then called for a "go around." However, the first officer did not add power for a go-around, and the captain did not take control of the airplane. Both pilots reported that, when the airplane was about 30 ft above ground level (agl), they felt a sensation that the airplane had "stopped flying" with a simultaneous left roll, which is indicative of an aerodynamic stall, followed by an immediate impact with terrain. After striking obstructions that completely separated the right main landing gear and the right flap, the airplane came to rest upright in the dirt on the side of the runway about 4,000 ft from the initial impact point. The airplane sustained substantial damage to the fuselage and both wings. All eight occupants evacuated through the main cabin door. There was a substantial fuel spill but no postimpact fire. Both pilots reported no mechanical malfunctions or failures of the airplane, and neither pilot reported an uncommanded loss of engine power. Data from the enhanced ground proximity warning system showed that seven warning events occurred in the last 3 minutes before the accident. The first warning was for "sink rate," and it occurred when the airplane was about 1,317 ft agl and in a 3,400-ft-per-minute descent. The last warning was for "bank angle," and it occurred about 10 seconds before touchdown as the airplane exceeded 42 degrees of bank when it was about 200 ft agl. The wind recorded at the airport at the time of the accident would have resulted in a 12-knot variable tailwind with gusts to 18 knots. The evidence is consistent with the first officer flying a nonstabilized approach with a decreasing airspeed during low-level windshear conditions. The first officer did not properly compensate for the known low-level windshear conditions and allowed the airspeed to continue to decrease and the bank angle to increase until the airplane experienced an aerodynamic stall.
On June 7, 2012, about 1224 mountain daylight time, a Learjet 60, N500SW, was substantially damaged when it impacted terrain and obstructions during landing at Aspen-Pitkin County Airport (ASE), Aspen, Colorado. The two airline transport pilots and the six passengers were not injured. The airplane was registered to and operated by Performance Aircraft Leasing, Inc. under the provisions of 14 Code of Federal Regulations Part 91, as personal flight. Day visual meteorological conditions prevailed and an instrument flight rules flight plan was filed. The airplane departed Opa-Locka Executive Airport (OPF), Miami, Florida, about 1020 eastern daylight time and was destined for ASE.While on a left downwind for a visual approach to runway 15 the tower controller informed N500SW about a Citation that landed about 10 minutes prior and reported low-level wind shear with a 15-knot speed loss on short final, and N500SW acknowledged. During the arrival to ASE the first officer was manipulating the controls and was seated in the left cockpit seat. The captain was seated in the right seat. While on a left base the first officer used spoilers and maneuvered the airplane in an "S-turn" on final to correct for a too steep approach. Close to touchdown, with airspeed decreasing, and responding to the calls from the captain for "power", the first officer advanced power slightly. Airspeed continued to decrease and the captain called for a "go-around", but the first officer did not add power for a "go-around", and the captain did not take control of the airplane. When the airplane was about 30 feet above ground level (agl) both pilots reported the airplane suddenly "stopped flying" with a simultaneous slight left roll and an immediate impact with terrain. The airplane impacted to the right of and short of the runway threshold, damaged runway threshold lights, traveled diagonally across the runway, and exited the left side of the runway. It continued moving in the dirt on the left side of the runway and struck obstructions which completely separated the right main landing gear and the right flap and resulted in substantial damage to the fuselage and both wings. The airplane came to rest upright in the dirt on the right side of the runway about 4,000 feet from the initial impact point and about 400 feet east from the airport fire station. All eight occupants evacuated through the main cabin door. There was a substantial fuel spill but no postimpact fire. Aircraft rescue and firefighting (ARFF) crews responded immediately and laid down a protective blanket of foam on the fuel spill. A postaccident download of data from the Enhanced Ground Proximity Warning System (EGPWS) showed seven warning events had been recorded in the last three minutes before the accident. The first EGPWS warning was for "sink rate" and showed the airplane was in a 3,400 feet per minute descent when at an altitude of about 1,317 feet agl. About 10 seconds before touchdown another EGPWS warning for "bank angle" showed the airplane exceeded 42 degrees of bank when at an altitude of about 200 feet agl and at a calibrated airspeed (CAS) of about 135 knots. The CAS continued to decrease and was about 127 knots just before touchdown. Both pilots reported there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation, and neither pilot had any doubt of the engines producing desired power. At 1153 MDT, ASE reported wind from 020 degrees at 7 knots with gusts to 16 knots, wind direction variable between 350 degrees and 060 degrees, visibility of 10 miles or greater, sky clear, temperature 23 degrees Celsius (C), dew point temperature -6 degrees C, and altimeter setting 30.13 inches of Mercury. At 1225 MDT, ASE reported wind from 270 degrees at 12 knots with gusts to 18 knots, wind direction variable between 240 degrees and 300 degrees, visibility of 10 miles or greater, sky clear, temperature 24 degrees C, dew point temperature -10 degrees C, and altimeter setting 30.13 inches of Mercury. ADDITIONAL INFORMATION: The ASE airport website recommends the following about approach procedures: "Establish the inbound flight path to require no more than a 20-degree bank angle to follow the noise abatement track". Federal Aviation Administration (FAA) Pilot's Handbook of Aeronautical Knowledge states in Chapter 11: "Ground topography (such as mountains, valleys and canyons) … can break up the flow of the wind and create wind gusts that change rapidly in direction and speed (which) can affect the takeoff and landing performance of any aircraft and can present a very serious hazard ... Due to the effect terrain has on the wind in valleys or canyons, downdrafts can be severe". "Low-level wind shear is a sudden, drastic change in wind speed and/or direction over a very small area. Wind shear can subject an aircraft to violent updrafts and downdrafts, as well as abrupt changes to the horizontal movement of the aircraft. While wind shear can occur at any altitude, low-level wind shear is especially hazardous due to the proximity of an aircraft to the ground. Directional wind changes of 180 degrees and speed changes of 50 knots or more are associated with low-level wind shear. The rapid changes in wind direction and velocity change the wind's relation to the aircraft disrupting the normal flight attitude and performance of the aircraft. During a wind shear situation, the effects can be subtle or very dramatic depending on wind speed and direction of change. For example, a tailwind that quickly changes to a headwind causes an increase in airspeed and performance. Conversely, when a headwind changes to a tailwind, the airspeed rapidly decreases and there is a corresponding decrease in performance. In either case, a pilot must be prepared to react immediately to the changes to maintain control of the aircraft". FAA AC 120-108 states "A stabilized approach is a key feature to a safe approach and landing (and is) characterized by maintaining a stable approach speed, descent rate, vertical flight path, and configuration to the landing touchdown point ... at a rate of descent no greater than 1,000 feet per minute (fpm)" FAA Publication FAA-P-8740-60 "Tips on Mountain Flying" states the following about approaches and landings at mountain airports: "Plan to fly a stabilized approach to the desired touchdown spot. Since mountain winds are sometimes tricky, be aware of wind shear and go around if necessary". FAA Approved Airplane Flight Manual (AFM) Learjet 60 Limitations in section I states: maximum landing tailwind component is 10 knots; Normal Procedures in section II states: "It is recommended that if turbulence is anticipated due to gusty winds, wake turbulence, or wind shear, the approach speed be increased. For gusty wind conditions, an increase in approach speed of one half the gust factor is recommended" ... Go Around Procedures in section II states: "Thrust Levers – Select T/O detent ... Climb at approach climb speed ... accelerate to Vref plus 20". Other data from the AFM states that the Vref speed is 134 knots, and the Vapp speed is 146 knots for operations at a weight of 17,500 pounds to a runway at 7,500 foot elevation with a dry runway, zero wind, and zero runway gradient.
The first officer’s failure to maintain adequate airspeed and his exceedance of the airplane’s critical angle-of-attack during the final approach in known low-level windshear conditions, which resulted in an aerodynamic stall. Contributing to the accident were the first officer’s failure to initiate a go-around when commanded and the captain's lack of remedial action when he recognized that the approach was unstabilized.
Source: NTSB Aviation Accident Database
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