Summary
On January 6, 2011, at 1101 central standard time, a Gates Learjet 35A (registration N800GP) operated by Priester Aviation LLC was substantially damaged during a hard landing and runway excursion on runway 22 at Abraham Lincoln Capitol Airport (SPI), Springfield, Illinois. The flight was conducted under 14 CFR Part 135 on an IFR flight plan. The aircraft departed from Chicago Midway International Airport (MDW) at 1034 with an intended destination of SPI. The pilot and one passenger sustained minor injuries; the copilot and three other passengers were not injured.
Flight History
According to the pilot, the airplane was de-iced before takeoff from MDW. The departure and descent were normal. The aircraft was in clear air during cruise and re-entered clouds about 5,000 feet mean sea level (msl) on descent, remaining in clouds until descending below the cloud layer about 5 miles from the runway. The pilot noted a trace of rime ice on the wing tip tank and windshield during the descent and approach. The master warning and stick shaker activated on short final. The airplane impacted left of the runway centerline, then departed the right side of the runway, crossed a slight rise, and came to rest in grass.
The copilot, who was pilot flying from the left seat, reported using the autopilot initially and then hand-flying after descending below clouds. The anti-icing system was on during cruise but was turned off upon intercepting the ILS glide slope. He observed light frost on the outboard wing and tip tank during the approach. Reference speed was 119 knots, target airspeed 124 knots. The copilot slowed the airplane earlier than usual to extend flaps and gear, aiming for higher engine power to improve anti-ice effectiveness. On final, the stick shaker activated; he applied full power. The left wing dropped, causing a veer to the left. He attempted to correct right. The airplane touched down, and after stopping, the captain directed evacuation.
One passenger reported lateral movement, sinking, left wing drop, and left-to-right “flip-flop” before a hard bounce. Another passenger noted the left windshield was obscured, and the airplane veered left before the accident sequence. The cockpit voice recorder (CVR) captured the flight being cleared for the ILS approach at 1055:51, and the pilot reported descending into cloud tops at 4,100 feet msl. At 1056:30, the copilot noted the anti-ice system was off. At 1058:49, the copilot noted wing anti-ice off and engine nacelle anti-ice on. At 1101:01, a gasp and command “full power” were recorded, with stick shaker at 1101:05 and impact sounds beginning at 1101:06.
Aircraft and Crew
The pilot, age 44, held an ATP certificate with Learjet 35 and CL-600 type ratings, and had about 5,932 total flight hours (827 in Learjet 35). The copilot, age 25, held an ATP certificate with a Cessna Mustang type rating, and had about 1,657 total flight hours (802 in Learjet 35). The aircraft, a Gates Learjet 35A (serial number 158), was manufactured in 1978, powered by two Honeywell TFE731-3-2AP turbofan engines. It was maintained under a continuous airworthiness inspection program, with the most recent inspection completed on June 21, 2010, at 16,321.4 hours total time. The airframe had accumulated about 16,506 hours at the time of the accident.
Weather and Airport Information
At 1052, weather at SPI included wind from 300 degrees at 14 knots gusting 19, 10 miles visibility, overcast clouds at 1,600 feet agl, temperature -2°C, dew point -6°C, altimeter 29.78 inHg. At 1101, two-minute averaged wind was from 289 degrees at 12 knots, peak 15 knots. The CVR indicated that the flight was notified of icing conditions; another airplane had reported light rime ice on approach. Runway 22 is 8,001 feet long by 150 feet wide, with a touchdown zone elevation of 598 feet. The ILS approach had a decision altitude of 798 feet msl (200 feet agl) and a glide slope angle of 3.00 degrees. An aircraft arresting system was present but stowed.
Wreckage and Impact Information
The airplane came to rest upright in a grassy area northwest of runway 22, oriented about 360 degrees. The right tip tank separated from the wing and showed fire discoloration. The right flap separated. All three landing gear assemblies separated from the airframe. Scrape and paint transfer marks on the runway started at the left edge, curving back to the runway and exiting right side about 1,300 feet from the threshold. The fuselage remained intact; the left wing was bent upward about 10 degrees at the outboard aileron end. Flight control continuity was confirmed. Both flap actuators corresponded to 40-degree (full) flap deflection.
Tests and Research
Functional testing of the engine bleed air modulating valves showed no anomalies consistent with loss of bleed air to the anti-ice system, though some deviations were noted. Temperature indicators showed correct indications in the cool-to-normal range but slight deviations above normal. A representative weight and balance calculation indicated the flight was within limits; landing weight was about 13,515 lbs, corresponding to a reference speed of 121 knots and required landing distance of about 2,700 feet. A vehicle performance study showed the airplane descended on a 3.30-degree glide path during the final 8 miles, with an average descent rate of 730 feet per minute. Average ground speed in the last 30 seconds was about 116 knots; calculated airspeeds ranged from 108 to 114 knots, and angle-of-attack exceeded the stick shaker threshold of 11.6 degrees.
Additional Information
The airplane flight manual stated that anti-ice systems should be turned on prior to operation in icing conditions. It warned that even small ice accumulations can cause a stall before stick shaker activation. The manual included procedures for wing heat failure and inadvertent icing encounters, specifying speed increases and landing distance factors if ice is present. The accident flight was below the weight limit for landing with full anti-ice on.