N4914ACessna T310R · 1978

On March 19, 2011, about 1605 mountain daylight time, a Cessna T310R, N4914A, collided with terrain during a missed approach at Bert Mooney Airport (BTM), Butte, Montana. The pilot was operating the airplane under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot sustained fatal injuries. The airplane sustained substantial damage, and was consumed by a post crash fire. The cross-country personal flight departed Great Falls International Airport (GTF), Great Falls, Montana, about 1520, with a planned destination of Butte. Instrument meteorological conditions prevailed, and an instrument flight rules (IFR) flight plan had been filed.

A witness, who was located in his residence at an elevation of about 5,600 feet mean sea level (msl), 3.5 miles northwest of the arrival end of runway 15, reported that snow began to fall in the area about 1540. About 1600 he was located at the east-facing window in his living room, because his attention was drawn to the snow, the intensity of which had increased. He stated that the area is susceptible to snow at this time of year, however, this snow fall was unusually heavy, and obscured his view across the street. The snow was blowing horizontally from west to east, and he continued to watch as it created unusual "eddy effects" as it swirled around his house. He then became aware of a very loud airplane engine sound, so loud that his reaction was to duck. He stated that he lives close to the normal flight path of the airport, and was very familiar with the sound of airplanes; however, this was much louder, and although he could not see the airplane, it appeared to be much closer than usual. He stated that he did not hear the sound of an explosion or impact.

Another witness located in his office on the campus of Montana Tech, about 4 miles northwest of the arrival end of runway 15, reported similar weather conditions and aircraft sounds about the same time. By the time he left his office, about 2 hours later, he observed vehicles in the parking lot encrusted with a layer of 1.5- to 2-inch-thick snow and ice.

The Federal Aviation Administration (FAA) provided radar and voice communication data for the flight, which revealed that the pilot was receiving radar vectors from the Salt Lake Air Route Traffic Control Center (ARTCC). About the time of the accident, the ARTCC controller for the sector, which included BTM, was providing radar vectors for multiple aircraft, including the accident airplane, and a Canadair Regional Jet (CRJ-200) operated SkyWest Airlines as Flight 4658. The SkyWest airplane was also destined for BTM.

The radar data revealed a target displaying a 4636 beacon code corresponding to N4914A, 90 miles northeast of BTM at 1530:00. Over the course of the next 19 minutes, the target maintained a track of 205 degrees true, at a Mode C reported altitude of 13,300 feet. At 1549:04, the pilot made a radio transmission to air traffic control reporting his altitude as 13,000 feet. The air traffic controller responded, and asked if the pilot he had checked the weather for BTM. The pilot responded that he was about to, and 27 seconds later, the air traffic control provided weather information for BTM that was recorded at 1538. The controller reported winds of 290 degrees at 9 knots, gusting to 16, with 1/3 mile visibility, snow, fog, few clouds at 800 feet, a broken ceiling of 1,400 feet, and an overcast ceiling at 2,200 feet. The pilot then responded, "We've picked that up, uh that just changed on us in here, in the last little bit." The air traffic controller replied that the weather had recently changed, and that although the visual approach was available earlier, the conditions were now deteriorating. The controller then stated, "Get back to me if you want to continue inbound or go somewhere else." The pilot replied, "...let's plan on going ahead and we'll..., looks kind of scattered and broken where I'm at." The controller asked the pilot to confirm that he wanted to start the initial approach, and the pilot responded, "... let's try that, and then if we have to, we'll go back to Helena."

At 1551:01, the controller responded that he observed N4914A established on Victor Airway 113, flying towards EVVER intersection. He then cleared the pilot for the "ILS Y RWY 15" approach, directing him to fly direct to MAGIC intersection, crossing it at or above 12,000 feet. The pilot read back the instructions, and radar data indicated that the airplane then initiated a descent towards MAGIC intersection.

The controller then made contact with SkyWest Flight 4658, informing the crew that they were the number two aircraft for the approach. The SkyWest pilot then responded, "We are just talking about what we are going to do here, if we could just stay at three zero zero for a minute that would be better for us." The controller then cleared the SkyWest airplane to maintain flight level three zero zero, and stated, "As you may have heard, the conditions have changed somewhat, now let me know what you would like to do and I will get you a new airport if you need it."

About 4 1/2 minutes later the SkyWest pilot reported, "We'd like to start down and get lower just in case the visibility comes up there and we can shoot the approach, but we can't stay for too long, we are going to have to head over to Bozeman in about 5 minutes or so." The controller subsequently cleared the airplane to hold over the Coppertown (CPN) Very High Frequency Omni-directional Range (VOR) at 16,000 feet.

At 1558:24, N4914A reached MAGIC intersection at an altitude of 11,150 feet. The controller reported that radar services were terminated, and cleared the accident pilot to switch to the advisory frequency, with instructions that he could call back if he elected to perform a missed approach. The pilot read back the instructions.

The target then crossed over MAGIC intersection, and began a right turn to the northwest. The turn was consistent with an entry into the published holding pattern, for the ILS 15 Y Approach. The last radar return from the airplane was recorded 36 seconds later, at 1559:00. That return indicated that the airplane was at 11,200 feet, and on a track of about 330 degrees. Shortly thereafter, the SkyWest pilot called requesting to discontinue the hold, and divert to Bozeman. The controller subsequently cleared the airplane to fly directly to Bozeman.

At 1604:24, the pilot of N4914A reported that he was performing the missed approach. The controller then responded with the BTM altimeter setting, instructions to climb to and maintain 15,000 feet, and a request for the pilot's intentions. The pilot then responded that he would begin the climb. The controller asked if he would like to divert to Helena, and after a 10-second pause, the pilot confirmed that he would like to do so. The controller then instructed the pilot to report leaving 12,000 feet, stating that he would be able to pick him back up on radar at that altitude. However, for the next 15 seconds the pilot did not respond. Shortly thereafter, a call of "Mayday Mayday" was heard on the controller's radio frequency. For the next 35 minutes, the controller unsuccessfully attempted to make contact with the pilot of N4914A both on the aircraft emergency frequency, and by utilizing airborne aircraft in the Butte area to relay messages. During that period a Pilatus PC-12 airplane performing an air medical mission also cancelled an approach into BTM, after the controller updated that airplane with the 1653 automated weather report, which indicated winds of 330 at 8 knots, 1/4 mile visibility with snow, freezing fog, broken ceilings at 400 and 900 feet, and overcast at 1,400 feet.

A review of FAA airman records revealed that the pilot held a commercial pilot certificate with ratings for airplane single-engine land, multiengine land, and instrument airplane. He held a third-class FAA medical certificate issued in March 2010, with the limitation that he must wear lenses for near and distant vision.

No personal flight records were located for the pilot, and they were presumed to be consumed in the postaccident fire. Examination of the aeronautical experience listed in the pilot's 2010 application for his FAA medical revealed that he reported a total of 1,750 flight hours, with 30 hours logged in the last 6 months. The pilot was issued his private pilot certificate in 1982, and subsequently received his instrument rating in 1988. According to his multiengine rating application, dated April 19, 2003, he had amassed a total of 170 hours of instrument flight experience, 89 of which was logged utilizing a training device. The pilot's aircraft insurance company provided a record of pilot qualifications, which the pilot had completed in July 2010 as part of his application for insurance coverage for N4914A. At that time, he reported a total experience of 1,745 flight hours, 52 of which were in multiengine airplanes. BTM was the pilot's home airport.

The, six-seat, low-wing, retractable-gear airplane, was manufactured in 1978. It was powered by two fuel injected, turbo-charged, Continental TSIO-520 engines, and equipped with McCauley three-blade, constant-speed propellers.

Due to the damage sustained to the airplane, the total flight time could not be determined. Review of the airplane maintenance records revealed that the most recent airframe and engine annual inspection was completed on December 11, 2009, at a total airframe time of 4,259.0 flight hours. At that time the right engine, serial number 176624-R, and the left engine, serial number 176625-R, had accumulated 1809.4 flight hours each since their last overhaul in January 1994.

The records documented 11 maintenance events since the December 2009 annual inspection. The last of those was recorded on December 9, 2010. No record of an annual inspection subsequent to the December 2009 inspection, 15 months prior, was located. The most recent documented test of the airplane's transponder, static, and altitude reporting systems was dated February, 12, 2008. FAA regulations require those tests every 24 calendar months.

The airplane was equipped with its original NAV-O-MATIC 400B two-axis autopilot, which was configured with a horizontal situation indicator (HSI), and capable of providing flight control necessary for instrument approaches. Original equipment also included the Cessna "Known Icing Conditions" deice system kit, which was comprised of an electric deicing pilot's windshield panel, wing and empennage pneumatic deice boots, heated pitot head and static ports, and propeller deice boots. A supplemental oxygen system tank was located within the wreckage.

The airplane was equipped with navigational and flight instruments suitable for flight in instrument meteorological conditions. Additional instrumentation included an L-3 Avionics Stormscope WX-1000 lightning detection system, a Garmin 530AW, Wide Area Augmentation System capable - Global Positioning System (GPS)/Navigation/Communication transceiver, and a Garmin GDL-49 XM Satellite data link transceiver. According to the manufacturer, the GDL-49 is capable of providing weather data delivery to the 530AW unit through use of the Sirius XM Satellite Radio network.

The pilot purchased the airplane in July 2010. The prior owner was also the airplane's current mechanic. The prior owner reported that after the sale, he continued to fly the airplane and share the maintenance costs with the pilot. He stated that the pilot would often perform maintenance on the airplane, but under close supervision.

BTM airport was equipped with an automated surface observation system, which disseminated and transmitted Meteorological Aerodrome Reports (METARs) and special reports surrounding the period of the accident. The observations indicated that visual flight rules (VFR) weather conditions prevailed at BTM during the morning hours, including the time of the airplane's departure from GTF, followed by deterioration to IFR, and then low IFR (LIFR) conditions during the flight. LIFR conditions are defined as a ceiling less than 500 feet and/or visibility 1/2 mile or less.

At 1518, 2 minutes before the airplane's departure from GTF, a special weather report for BTM was issued indicating winds from 290 degrees at 15 knots, gusting to 23 knots, with 9 miles visibility, scattered clouds at 2,400 feet, and an overcast ceiling at 7,000 feet. Two minutes later another report was issued indicating similar ceilings but with a visibility of 2 miles in light snow, with a temperature of 2 degrees C, and a dew point of minus 3 degrees C.

Multiple special reports for BTM were issued throughout the period of the flight, all indicating a rapid decrease in visibility and ceilings, along with gusting and shifting wind conditions. The final special report issued prior to the accident was at 1553, and indicated winds from 300 degrees at 8 knots, with 1/4 miles visibility, snow, freezing fog, broken clouds at 400 and 900 feet, with an overcast layer at 1,400 feet, and a temperature and due point of minus 1 and minus 2 degrees C, respectively.

Pilot Reports

Four pilot reports (PIREPS) were transmitted for the Montana area surrounding the time of the accident. Two of the reports indicated icing, with the first reporting light to moderate rime ice over Helena (HLN) with no altitude reported. The second report indicated light rime ice at 11,000 feet, 69 miles east of Billings (BIL).

Forecasts

The forecast during the accident period for the area west of the Continental Divide was for overcast clouds at 8,000 feet msl with tops to 25,000 feet, and widely scattered light rain and snow showers. The southwestern mountain region expected similar conditions with broken clouds at 10,000 feet msl, overcast at 15,000 feet with tops to 25,000 feet with occasional light rain and snow, and isolated thunderstorms with tops to 28,000 feet.

AIRMETs (airmen's meteorological information) for the accident period revealed that the accident site was located within an area covered by an advisory for mountain obscuration and icing conditions, and bordered immediately east of one of the areas of expected IFR conditions.

The BTM terminal area forecast issued at 1140 MDT predicted VFR conditions from 1500 through 2100 with wind from 250 degrees at 11 knots gusting to 18 knots, visibility better than 6 miles in light snow, with a broken ceiling at 6,000 feet above ground level (agl) in cumulonimbus clouds.

Immediately prior to the accident at 1545 and approximately 1/2 hour after, snow began at the airport; the forecast for BTM was amended, with expected IFR conditions at the time of the airplane's arrival. The forecast from 1600 became visibility 1/2 mile in moderate snow and fog, scattered clouds at 800 feet agl, ceiling broken at 1,400 feet, overcast at 2,200 feet.

The National Weather Service Current Icing Product (NWS CIP) is an automatically-generated index suitable for depicting areas of potentially hazardous airframe icing. A CIP analysis for 1600 at 10,000 feet resulted in a greater than 50 percent probability of icing conditions at 10,000 feet msl over southwestern Montana and the accident site, with values reaching 70 percent southeast of the accident site near the Wyoming and Idaho border.

Weather Briefing

The pilot filed an IFR flight plan, and received a weather briefing about 25 minutes prior to departure, utilizing the Computer Sciences Corporation Direct User Access Terminal Service system. The pilot selected a 'low altitude weather briefing' during the session. The data provided during that session included Terminal Aerodrome Forecasts, Severe Weather Outlook, Current weather conditions, and NOTAMs. The pilot filed a plan requesting a route of flight from GTF to HLN to EVVERS intersection, at an altitude of 13,000 feet. He reported a total of 3 hours of fuel on board, and did not indicate an alternate airport destination.

Satellite Weather System

The pilot maintained a current monthly subscription to the Sirius XM Satellite Radio, XMWX Satellite Weather 'Aviator' service at the time of the accident. Utilizing this subscription, the Garmin 530AW supported the following weather services: Weather Surveillance Radar (NEXRAD), graphical METAR, text-based METAR, Wind, and Graphical Temperature/Dew Point. According to the Garmin 530AW Pilots Guide, the NEXRAD data did not provide sufficient information to determine cloud layers or precipitation characteristics (hail vs. rain, etc).

Baron Services, Inc., provided weather data compilation and delivery to the Garmin system through the Sirius XM Satellite Radio network. According to representatives from Baron, no data outages existed during the period of the accident.

The ILS Y Runway 15 Approach utilizes a glide slope and a final approach course of 151 degrees magnetic, with an initial approach fix (MAGIC) located at the intersection of the glide slope and the CPN VOR 027 degree radial. The charted minimum altitude for holding at MAGIC is 10,000 feet. The CPN VOR was utilized as the holding fix that was part of the missed approach procedure, and was located about 13 miles northwest of BTM. The missed approach procedure specified a climb to 7,300 feet, followed by a climbing right turn to 9,100 feet via the CPN VOR 113 degree radial. The wreckage was located along the CPN 086 radial, about midway between the airport and the missed approach hold location. The published landing minimums for the approach required 4 miles visibility, with a decision height of 6,711 feet msl, which was 1,188 feet agl.

FAA regulations prohibit scheduled air carrier aircraft from proceeding past the final approach fix of an instrument approach unless the reported meteorological conditions meet or exceed the applicable IFR landing minimums for the aircraft and approach procedure. No such limitations apply to general aviation (Part 91) operations.

BTM had two runways: runway 15/33, which was 9,001 feet long and 150 feet wide, and runway 11/29, which was 5,100 feet long and 75 feet wide. The airport was not serviced by an air traffic control tower, and approach and departure services were provided on a continuous basis by the Salt Lake ARTCC. The airport was located within a valley, and was at an elevation of 5,550 feet. The airport was surrounded by mountainous terrain with elevations between 6,000 and 10,000 feet.

The airplane wreckage was located on the south-facing slope of rolling hills, about 5.5 miles northwest of the airport, at an elevation of about 5,700 feet. The area surrounding the site consisted of grassland, dispersed with rocky outcroppings, tree saplings, and pine trees ranging in height from 6 to 20 feet. The airplane came to rest nose down on a group of rocks on an approximate heading of 180 degrees magnetic. Both engines remained in the vicinity of their wing mounts, in a 60-degree nose down attitude. The entire cabin sustained crush damaged reducing its overall length to approximately 5 feet, with the remnants consumed by fire. Both wings sustained accordion-like crush damage through to their forward spars, perpendicular to the leading edge. The remaining sections of the wing skins, aft cabin, and tailcone were fire consumed. The vertical stabilizer and rudder came to rest downhill of the wings within the burnt remnants of the cabin. The horizontal stabilizer and elevator came to rest on top of the aft wing spar. The primary debris field radiated about 60 feet downhill to the south of the main wreckage, and consisted of the upper cabin skin, flight instruments, fragmented wing, fuselage, and fuel tank skins. A 40-foot-tall power transmission pole was located about 25 feet east of the main wreckage, and its transmission cables traversed the debris field diagonally. No damage was noted to the power lines, poles, or any surrounding trees, with the exception of one sapling next to the fuselage, which remained intact but sustained thermal damage. The debris field consisted of smaller fragments, and extended about 80 feet towards the base of a ravine. All sections of the airplane were accounted for at the accident site.

The airplane fragmentation signatures, combined with the position of the wreckage relative to the slope, was consistent with a wings-level, 50-degree nose-down attitude at the time of impact.

A postmortem examination was conducted by the State of Montana Forensic Science Division. The cause of death was reported as the effect of blunt force injuries.

Toxicological tests on specimens from the pilot were performed by the FAA Civil Aeromedical Medical Institute. The results were negative for all screened drug substances and ingested alcohol. Refer to the toxicology report included in the public docket for specific test parameters and results.

Airframe

The airframe was examined at the accident site, and then recovered to a remote storage facility for further airframe and engine examination.

The majority of the autopilot, navigation, deicing equipment, and supplemental oxygen system components sustained significant fragmentation damage, or were consumed by postaccident fire. Therefore, their operational status at the time of the accident could not be determined. The engine tachometer and airplane turn and slip indicator were located in the debris field. The tachometer needles indicated a left engine speed of 2,550 rpm, and a right engine speed of 2,425 rpm. The turn and slip indicator sustained crush damage to its case and indicator needle; a paint imprint and scratch in the shape of the indicator needle was noted on the instrument face in the area corresponding to a left turn of about 6 degrees per second.

Examination of the flight controls revealed multiple breaches to the push-pull tubes and cables. The flap system was examined, and a determination of the flap position was made based on the chain link position at the flap motor. According to the Cessna representative, the chain link settings were consistent with a 15-degree flap position.

Two vacuum pumps were located in the debris field. The first pump (Airborne type 442CW) remained largely intact; disassembly revealed that the inner vanes and rotor were fractured. The cavity walls remained free of gouges or indications of distress. The pump's plastic shear coupling remained intact. The case and mounting pad of the second pump (Rapco type RA442CW) were the only items located; the inner cavity walls were free of circumferential gouges or indications of distress.

No evidence indicating either an in-flight fire, or bird-strike was observed.

Engines

The right engine remained partially attached to its wing mount, and came to rest facing down against a group of rocks. The engine sustained crush damage primarily around the forward crankcase, which separated the number six cylinder head, piston, and crankshaft forward of the number five connecting rod journal. The number five cylinder was separated from the case, and remained attached to the engine by its piston rod at the crankshaft. Multiple rocker covers were separated from their respective cylinders, exposing the rocker valve assemblies. A borescope examination of all cylinders revealed no foreign object damage, and all piston heads and combustion chambers exhibited light grey deposits. All exhaust valve heads exhibited symmetrical coloration. The propeller governor, alternator, propeller hub, fuel control, magnetos, throttle body, and induction manifold were fragmented and liberated from the engine. The engine sustained damage to the crankcase in the vicinity of the data plate mounting location, and the data plate was not recovered. Oil was noted within the crankcase, and no evidence of oil starvation was noted within the engine.

The turbocharger casing was separated from the induction and exhaust ducting. The turbine drive shaft, along with the induction and exhaust impeller, was liberated from the casing. All vane blades were bent, and also exhibited jagged surface damage features. Rotation of the impeller by hand resulted in smooth and free rotation through the turbine shaft housing. Examination of the inner chamber of the turbine scroll revealed radial gouging and scratches consistent with impeller rotation at impact.

Examination of the shared number five intake cam and number six cylinder cam lobe revealed wear signatures, scratches, and pitting to its lifting surface, which reduced its maximum lift dimension by about 1/8 inch. The remaining cam lobes were examined on the engine utilizing a lighted borescope; all lobes exhibited varying degrees of wear ranging from light polishing to about 1/8 inch of material loss. The number one exhaust lifter was removed, and revealed spalling and pitting damage to its cam contact surface.

The fuel manifold valve was separated from its mount and remained attached to two fuel lines. The divider was opened, and fluid consistent in odor to aviation gasoline was noted within the cavity.

The left engine remained attached to its mounts, came to rest facing down in a section of soft dirt, and sustained impact damage similar to that of the right engine. Wear signatures similar to those observed on the right engine were observed for the camshaft lobes, valve lifters, and spark plugs.

The propeller hubs for both engines were fragmented. All propeller blades were separated at the hub, and exhibited similar leading edge nicks, gouges, trailing edge wrinkling, and chordwise scratches. Each of the right propeller blades was missing about 6 inches of its tip, and all exhibited jagged tear patterns.

The Continental representative stated that the wear exhibited on the cam lobes and followers could result in an undetermined reduction in engine power, and that the damage would have resulted in a gradual reduction in engine rated power over its life, rather than a sudden loss of power. No documentation was recovered to indicate that engine oil samples had ever been submitted for analysis. No anomalies of the airframe remnants that would have precluded normal operation were noted. Refer to the engine and airframe reports included in the public docket for further details.

Autopilot and Deice System

The autopilot flight manual supplement applicable to the airplane model stated the following under the general description section:

"An autopilot disengage function is provided which automatically disengages the autopilot anytime the airplane pitches up or down more than a normal amount from a level flight attitude..."

The flight manual further states that the deice system is designed to remove ice after accumulation, rather than prevent ice formation. Moreover, during icing encounters, the surface deicing system should be activated when ice accumulates to a thickness of between 1/4 and 1/2 inches. An accumulation of a 1/2 inch of ice may cause a cruise speed reduction of up to 30 knots, as well as a significant buffet and stall speed increase.

The prior owner of the airplane reported that the autopilot would disengage under certain flight conditions, such as during turbulence. He did not believe this to be a technical problem, but more a function of the particular model of autopilot. By comparison, he currently owns another model Cessna 310, which was equipped with a different autopilot system. He stated that this autopilot was far less prone to disengaging in flight when compared to autopilot system in the accident airplane.

On the morning of the accident, the pilot brought the airplane to the prior owner in Great Falls to troubleshoot a 100-degree-low exhaust gas temperature reading on the left engine, number four cylinder. When they tried to diagnose, the readings were normal. They performed a borescope examination of the cylinders, and no discrepancies were noted. The pilot did not report any other problems with the airplane.

After the exam, they went out for lunch and discussed the return flight. During the discussion, the pilot talked about the weather forecast, and discussed his flight experience. During the discussion, the pilot stated that he had minimal flight experience in IMC conditions in the accident airplane.