NTSB Factual Report

HISTORY OF FLIGHT

On March 17, 2007, about 1430 eastern daylight time, a Cessna 500, N511AT, operated by Air Trek, Inc., was substantially damaged during landing at Beverly Municipal Airport (BVY), Beverly, Massachusetts. None of the four crewmembers or two passengers were injured. Instrument meteorological conditions prevailed and an instrument flight rules flight plan had been filed for the flight, which originated at Charlotte County Airport (PGD), Punta Gorda, Florida at approximately 1100. The air ambulance flight was conducted under 14 Code of Federal Regulations (CFR) Part 135.

During the descent into BVY, the flight crew was given, information 'Hotel' by air traffic control (ATC); with wind at 310 degrees at 8 knots, visibility 1 statute mile, a 500 foot overcast sky with mist, and good ground braking action. The given approach at BVY was the RNAV 16, circle-to-land Runway 34.

According to the flight crew, they advised ATC that their general operations manual (GOM) prohibited circling approaches with ceilings less then 1500 feet, and requested the GPS RUNWAY 16 approach at BVY. Reference speed was set to 97 knots. After passing the initial approach fix they entered the clouds at 3,500 feet mean sea level (msl), turned on the anti-ice system, and noticed that there was "quite a bit of wind" which they had to compensate for. Moments later, the copilot noticed that they were picking up a trace amount of rime ice on the windscreen; however, since neither pilot saw any ice on the wings, the deicing boots were never activated.

As they neared the final approach fix (FAF), they "added a notch" of approach flaps, and then added full flaps when they crossed the FAF. At 600 feet msl, they acquired the field and the precision approach path indicator (PAPI). Once established on the PAPI, speed was V-ref +10 (107 knots), and the approach to landing seemed normal until reaching approximately 100 feet above ground level. At this point, the flight crew experienced what the copilot described as a "burble," and the airplane rolled "steeply" to the right. The pilot stated that there was "no buffet and no warning." They attempted to roll wings level, and added power to arrest the sink, but were unsuccessful and the right wingtip struck the surface of the runway-overrun area.

After landing and taxiing to the ramp, the flight crew conducted a post flight inspection of the airplane. They noted that the right wing was bent upward about 10 degrees, and "Light rime ice" was present on the leading edges of the wings, horizontal stabilizer, and radome.

According to a customer service agent, after the airplane came to a stop on the airport ramp area, he also observed an accumulation of ice on the leading edges and nose of the airplane. He described it as a rime ice strip, about two inches top to bottom, covering the entire leading edge from wing tip to wing root. The white of the ice was "highly visible," although, he could see the wing's rubber boot through the ice in some areas, and estimated that approximately 90 to 95% of the wing boot was covered by the two-inch strip. On the nose of the aircraft he also witnessed a solid coverage of ice approximately 10-15 inches in diameter that was about 1/16 to 1/8 of an inch thick. Upon exiting the aircraft, he also observed the flight crew immediately go the right wing to inspect it and asked them, "What happened?" They replied, that they believed they had encountered "wind shear," when they came across the tree line on the approach to runway 16, and, "it was like the bottom just fell out on us."

The ATC tower controller also witnessed the event and stated that the airplane appeared to touchdown hard and on its right wing. When he asked the pilot if everything was all right, the pilot replied, "I believe so," and stated that they had experienced a wind shear on final. The ATC controller said he queried the crew of a Canadair Challenger that landed on runway 16 just after the mishap, if they had experienced any wind shear and they said they had not.

PERSONNEL INFORMATION

The pilot held an airline transport pilot certificate with multiple ratings including airplane multi-engine land, and a CE-500 type rating. According to records provided by Air Trek, the pilot had a total flight experience of 4,950 hours, with 3,200 hours in the accident airplane make and model. His most recent FAA first-class medical certificate was issued on October 25, 2006.

The copilot held an airline transport pilot certificate with multiple ratings including airplane multi-engine land and a B-737 type rating. According to records provided by Air Trek, he had a total flight experience of 25,982 hours, with 24.8 hours in the accident airplane make and model. His most recent FAA first-class medical certificate was issued on August 22, 2006.

AIRCRAFT INFORMATION

The airplane was manufactured in 1974, and had been modified with a Sierra Industries Incorporated, Citation Eagle (wing) modification. This modification had been originally developed by Advanced Systems Technology Incorporated (ASTEC) and was originally marketed as the "ASTEC EAGLE." The owner purchased the airplane on October 2, 1997. The most recent continuous airworthiness inspection was completed on February 28, 2007. At the time of the accident, the airplane had accumulated 22,015 total hours of operation. No recorders were installed.

METEOROLOGICAL INFORMATION

A weather observation taken about 11 minutes after the accident, included; wind at 300 degrees at 7 knots, visibility 10 miles, ceiling overcast at 500 feet, temperature 30 degrees Fahrenheit, dew point 28 degrees Fahrenheit, and an altimeter setting of 29.44 inches of mercury.

AIRPORT INFORMATION

BVY had two runways, oriented in a 09/27 and 16/34 configuration. Runway 16 was asphalt, and in good condition. It was equipped with a 4-light PAPI, a medium intensity approach light system, medium intensity runway edge lights, and non-precision markings. The total length of the runway was 5,001 feet, and its width was 100 feet.

WRECKAGE AND IMPACT INFORMATION

Post accident examination of the accident site and airplane by a Federal Aviation Administration (FAA) inspector revealed that, ground scars and impact signatures, which corresponded with the right wing striking the paved surface, existed approximately 100 ft before the displaced threshold.

The upper wing skin of the right wing/fuel tank had been breached, exposing the main spar. The spar was broken and the outboard portion of the right wing and aileron had been bent in an upward direction at an approximate 10-degree angle, seven feet inboard of the wingtip. No preimpact mechanical malfunctions were discovered.

TESTS AND RESEARCH

Warning Systems

According to the airplane manufacturer, an AOA system was optional, and no ice detector, or stall warning system was installed.

Stall warning was achieved aerodynamically, aided by stall strips on the inboard section of each wing. The strips would disrupt the airflow over the wing causing that area to stall first and accentuate the pre-stall buffet. This would alert the pilot of the impending stall by aerodynamic buffeting which would occur at "approximately VS1 +12 in the clean (flaps up) configuration, and VSO + 5 in the landing configuration."

Eagle Wing Modification

According to 14 CFR Part 25.1419, if an airplane manufacturer seeks certification for flight in icing conditions, the airplane must be able to safely operate in the continuous maximum and intermittent maximum icing conditions of appendix C.

As part of the supplemental type certificate for the ASTEC Eagle wing modification (STC SA645NW), additional icing tests and analysis were required by the FAA to demonstrate that the anti-icing performance of the Eagle system met those requirements, and that it's anti-icing performance was equivalent to, or higher than, the level of anti-icing performance of the Cessna 500.

Modifications to meet these requirements included a revised wing leading edge for the inboard portion of the wing. As the engines were mounted aft of this area, that portion of the wing leading edge directly ahead of the engine inlet was anti-iced to prevent possible damage to the engines by ingestion of ice shed from the wing leading edge and upper surfaces. The areas outboard of this area remained unmodified and continued to utilize pneumatic boots for de-icing. Anti-icing for both the Eagle and the Cessna 500 inboard wing was accomplished with electrical heaters. The heaters were identical in construction, installation and wattage distribution. The heaters only differed in that the chordwise heated length for the Eagle installation, was greater than for the Citation 500 installation, due to a larger impingement limit for the Eagle inboard wing.

According to ASTEC documentation, in flight measurements of the engine anti-ice panel temperatures were made on both the ASTEC EAGLE and a basic Cessna 500 airplane. Results of these tests indicated that the surface temperature distributions were similar for both airplanes. During testing the EAGLE anti-ice system also demonstrated greater energy capability. Based upon the measured temperatures and the energy comparisons, the FAA considered that, the EAGLE anti-ice panel provided engine ice protection equivalent to that of the basic Cessna 500 with reduced risk of runback problems in the wing-body intersection region, and a higher degree of ice protection than the basic airplane.

Anti-Ice and De-Ice Systems

According to the Cessna Citation (Cessna 500) operating manual, the anti-ice systems were designed to prevent ice formation on the pitot tubes, static ports, windshields, angle of attack probe (if installed), and to protect against engine ice damage. The various anti-icing functions used electrical power or engine bleed air and were actuated by switches on the left switch panel and control knobs on the co-pilot's panel. Cessna Aircraft Company advised that, "the Anti-ice systems should be turned on when operating in visible moisture with an indicated OAT between +4°C and -30°C (+40°F and -22°F)."

The airframe de-ice system provided for removal of ice formed on the leading edge of the wing (outboard of the heated area) and tail aerodynamic surfaces by the pneumatically expanded boots. The airframe de-ice boots were controlled by a three-position SURFACE DE-ICE switch which was spring-loaded to OFF and provided two six-second cycles following momentary actuation. There was no automatic or continuous mode.

Boot cycling, was controlled by three control valves. On the first six second cycle, one valve opened the inflate line to the vertical stabilizer and the left horizontal stabilizer. Two control valves then actuated on the second cycle to direct air to both wings and the right horizontal stabilizer. The time circuit would elapse twelve seconds after initiation and de-energize the control valves. The boots then deflated by bleeding the air back through the control valve and dumping it overboard. The boots were held deflated by vacuum.

In the event the boots remained inflated or it was desirable to stop boot inflation and terminate the cycle, the pilot could place the surface de-ice switch to the RESET position. This would override the timer circuit and immediately deactivate the control valves. It was not necessary to go to the reset position after every boot cycle, and returning the switch to the OFF position would prepare the system for the next actuation.

Satisfactory operation of the deice boot cycle was verified by illumination of the surface de-ice annunciator light and "visual inspection of the wing leading edges." Illumination of the surface de-ice light indicated there was bleed air pressure to the boots for inflation. The light would momentarily blink off, between each cycle.

The operating manual stated that, the operation of the boots should be functionally checked, "prior to icing encounters while on the ground, or in flight with the OAT above -40° C (-40°F)" and that, "Surface de-ice should be used when ice buildup is estimated between 1/4 and 1/2 inch thickness." The manual also stated that, "Early activation of the boots may result in ice bridging on the wing," and added that, "If accumulation is in excess of 1/2 inch, boot cycling may not clear it." A wing inspection light was also provided to illuminate the left wing to "observe ice buildup during night flight." No abnormal or emergency procedures were listed in the event of a system failure.

Post Accident Interviews

Both pilots had taken FAA approved training for the Cessna 500. During post accident interviews of the pilots by National Transportation Safety Board investigators, the pilots advised that they both had received systems training for the Cessna 500.

The copilot advised that during their "checks in the air," they never saw ice on the wings and that their was no requirement to increase the reference speeds in icing conditions or in conditions conducive to icing. He also stated that "boots have some adverse features," and "unless you have 1/4 to 1/2 inch of ice" you should not operate them, and that the information was contained in the study guide provided to him by the company as well as in Section II of the airplane operating manual.

The pilot advised that, he looked at the wing but saw no ice. He also stated that you do not want to "blow" the boots too soon as you can get a "hollowed area." He had also seen multiple on-line training videos, which included information on "tail plane icing." He had been informed about "hinge moment reversals" by another pilot, had just completed "icing training," and had heard of "ice bridging," at both Simuflight and Air Trek.

ADDITIONAL INFORMATION

Cessna Model 560

A Review of the Cessna 560 airplane flight manual (AFM) by Safety Board investigators revealed that like the Cessna 500 operating manual, the AFM for the Cessna 560 advised pilots to wait for ice to build before inflating the pneumatic de-icing boots, stating that, "The surface de-ice system should be used when ice buildup is estimated to be between one-quarter-inch and one-half-inch thickness. Early activation of the boots may result in ice bridging on the wing. If ice is allowed to accumulate in excess of one inch, boot cycling may not clear it." Unlike the Cessna 500 (which has a different wing design), in the section titled Operating Procedures Model 560 Normal Procedures, Approaches, it advised pilots not to wait for ice to build first. "When reconfiguring for approach and landing, and any ice accretion is visible on the wing leading edge, regardless of thickness, activate the surface de-ice system. Continue to monitor the wing leading edge for any reaccumulation."

In 1996, the FAA conducted evaluations of the Cessna 560. Evaluations of stall speeds and characteristics when operating in icing conditions were conducted. The evaluations were conducted partially as the result of two icing-related Cessna 550 and 560 accidents.

One accident had occurred on December 30, 1995, when a Cessna 560 crashed while circling to land in icing conditions in Eagle River, Wisconsin, fatally injuring the 2 occupants. The investigation revealed that about 1/8 inch of rime ice had accumulated on the left wing and horizontal stabilizer leading edges. The other accident occurred on January 2, 1996, when a Cessna 560 crashed while on final approach in icing conditions in Augsburg, Germany. The pilots reported that the airplane started to buffet, entered a stall, and rolled right. No stall warnings were activated during the flight. The investigation by the German Flight Investigations Bureau (FUS) revealed that about 2 mm (0.078 inch) of ice had accumulated along the leading edges of the wing. These evaluations resulted in modifications to the stall warning system to increase stick shaker speed in icing conditions, but did not change the procedures for pneumatic de-ice boot operation.

Comair Flight 3272

On January 9, 1997, the Safety Board investigated the accident involving Comair Flight 3272 in which 29 people were fatally injured. The Safety Board concluded that a sm

NTSB Probable Cause

The inadequate guidance and procedures provided by the airplane manufacturer regarding operation of the pneumatic de-icing boots. Also causal was the Federal Aviation Administration's inadequate directives which failed to require manufacturers to direct flightcrews to immediately operate pneumatic deicing boots upon entering icing conditions.