N758NHCessna R172K · 1979

On August 10, 2008, about 1223 mountain daylight time, a Cessna R172K, N758NH, and a Cirrus SR22, N8341, collided in midair about 5 nautical miles northwest of the Rock Springs-Sweetwater County Airport (RKS), Rock Springs, Wyoming. Both airplanes were destroyed by impact damage and fire. The student pilot, sole occupant of the Cessna, and the private pilot and passenger in the Cirrus were killed. The Cessna was registered to, and operated by, Franklin Aviation, Rock Springs. The Cirrus was registered to Renard Argent, Inc., Wilmington, Delaware, and operated by the pilot. Visual meteorological conditions prevailed. Both airplanes were operating under 14 Code of Federal Regulations Part 91. The Cessna departed Rock Springs Airport about 1155 on a local solo instructional flight for the purpose of practicing maneuvers; no flight plan was filed. The Cirrus departed Polson, Montana, about 0955, on a personal cross-country flight to Rock Springs; an instrument flight rules (IFR) flight plan was filed and activated.

According to Federal Aviation Administration (FAA) records, the pilot of the Cirrus contacted Salt Lake Center sector 19 at 0957, requesting an IFR clearance from Polson to Rock Springs. The flight was cleared to Rock Springs and assigned an altitude of 13,000 feet mean sea level (msl). At 1033, the pilot requested and received clearance to 15,000 feet msl. The flight continued uneventfully, and was handed off to Salt Lake Center sector 5 at 1203. At 1215, the pilot requested a lower altitude and was cleared to 10,000 feet msl. The controller issued the RKS altimeter setting and advised the pilot to expect a visual approach. At 1219, the pilot reported the airport in sight and was cleared for the visual approach. The sector 5 radar controller issued traffic advisories for numerous targets in the vicinity of Rock Springs and approved a change to advisory frequency, advising the pilot to cancel his IFR flight plan on his frequency or through Flight Service. The pilot responded by stating, "all right 8341 will start a report over your frequency when I get the other targets any idea what they are using there for runways?" At 1220:20, the controller stated that he did not know which runway was in use, and issued the current surface wind report for Rock Springs. The controller then issued another traffic advisory, advisory stating, “right now I’m showing one target it’s ah ah will be your eleven oclock your one oclock and ah about one zero miles north ah well primarily eastbound east north eastbound altitude indicates niner thousand five hundred." At 1220:47, the pilot responded, "8341 thank you." There was no further contact with the Cirrus.

Radar data was provided by the FAA and was obtained from the Rock Springs Air Route Surveillance Radar, located approximately 15 miles south of the airport. The data indicates that the Cessna was maneuvering northwest of the Rock Springs Airport, and the Cirrus was approaching the airport from the northwest while descending. Between 1219:59 and 1220:28, the Cessna completed a 180 degree turn from a southwesterly heading to a northeasterly heading. From 1220:27 to 1222:22, the Cessna maintained a northeasterly heading, climbed from 9,300 to 9,800 feet msl, and leveled out. About 1222:22, the Cessna turned approximately 20 to 30 degrees right and continued on that heading, level at 9,800 feet msl, until the last radar return recorded at 1222:42. From 1220:27 to 1222:42, the Cirrus descended from 11,300 to 9,700 feet msl on a heading of about 130 degrees magnetic. The data depict the two airplanes converging nearly perpendicular to one another. From 1220:50 to 1222:42, the Cirrus had an average ground speed of 195 knots and was descending at an average rate of 740 feet per minute. The Cessna had an average ground speed of 108 knots for the same time frame. The data suggests the collision took place about 1222:52, at an altitude of about 9,800 feet msl or about 3,300 feet above ground level (agl).

According to local authorities, several witnesses reported seeing a cloud of smoke and flaming debris falling to the ground.

The Cessna pilot, age 54, held a third-class medical and student pilot certificate that was issued on January 1, 2008. The certificate was issued with the limitation: must have glasses available for near vision. On the back of the certificate, there were endorsements for solo flight in Cessna R172K airplanes and for solo cross-country flight in airplanes dated April 10, 2008, and May 1, 2008, respectively.

Review of the Cessna pilot's logbook revealed that he had accumulated 64.3 hours of total flight time of which 11.6 hours were solo. All of the pilot's flight time was in the accident airplane. He had flown 9 hours in the 30 days preceding the accident. His most recent flight before the accident occurred on August 9, 2008; the flight was a local solo flight that lasted 2.0 hours.

According to the Cessna pilot's flight instructor, during the accident flight, the student pilot was to "review steep turns and possibly slow flight and stalls." The maneuvers were to be performed at an altitude of 9,000 feet msl. The instructor had previously practiced these maneuvers "as well as clearing turns before each maneuver and scanning techniques" during dual instructional flights with the student; their most recent flight together was on August 8, 2008.

The Cirrus pilot, age 67, held a private pilot certificate with single engine land and instrument airplane ratings. His most recent first-class medical certificate was issued on April 25, 2007, with the limitation: must wear corrective lenses. On January 2, 2008, he completed a biennial flight review in the accident airplane.

Review of the Cirrus pilot's logbook revealed that he had accumulated 1,434.8 hours of total flight time of which 1,316.4 hours were as pilot-in-command. The pilot had flown 671.3 hours in Cirrus SR22 airplanes. He had flown 22 hours in the 30 days preceding the accident.

Examination of the Cessna's maintenance records indicated that the 1979 model Cessna Hawk XP II received its most recent annual inspection on May 10, 2008, at a total time of 8,367.7 hours. As of that date, the engine, a Continental IO-360-AcKB, had accumulated 1,652.3 hours since major overhaul. Review of the maintenance records revealed no evidence of any uncorrected maintenance discrepancies.

The airplane was equipped with a Cessna 300 series avionics package that included, in part, two RT385A COM/NAV units and an RT359A transponder. Additionally, the airplane was equipped with a Narco AR850 altitude encoder providing Mode C capability to the transponder. The transponder antenna was mounted on the bottom of the fuselage.

The maintenance logbooks for the Cirrus were not located during the investigation. The airplane's maintenance history was established from work orders obtained from maintenance facilities where work had been performed on the airplane. Examination of these records indicated that the 2006 model Cirrus SR22 G3 received its most recent annual inspection on September 17, 2007, at a Hobbs meter time of 155.4 hours. As of that date, the engine, a Continental IO-550-N, had also accumulated 155.4 hours. The most recent maintenance action documented was performed on June 13, 2008, at a Hobbs meter time of 298.8 hours, and included an engine oil change and compliance with several service bulletins. Review of the work orders revealed no evidence of any uncorrected maintenance discrepancies.

The airplane was equipped with an Avidyne Entegra EXP5000 Primary Flight Display (PFD) and an Avidyne Entegra EX5000 Multi-Function Display (MFD). Its avionics included two Garmin GNS430 GPS/COM/NAV units, a Garmin GMA340 Audio Panel, a Garmin GTX 327 Mode C transponder, and a Honeywell KGP 560 Terrain Awareness and Warning System (TAWS).

Additionally, the airplane was equipped with an L-3 Avionics Systems SkyWatch SKY497 Traffic Advisory System. According to the supplemental flight manual for the Skywatch, the purpose of the system was "to advise the pilot of transponder equipped aircraft that may pose a collision threat." The supplemental flight manual stated that the SkyWatch monitors a radius of approximately 6 nautical miles around the aircraft by interrogating transponders in the monitored area and determining if a collision threat exists. To determine if a collision threat exists, the unit calculates the range, altitude, bearing, and closure rate of all transponder equipped aircraft within the 6 nautical mile range. When the unit detects an intruder aircraft within 0.55 nautical mile horizontal distance and plus or minus 800 feet relative altitude or detects an intruder aircraft is on a course that will intercept the Skywatch airplane's course within 20 seconds (non-altitude reporting intruder aircraft) or 30 seconds (altitude reporting intruder aircraft), the unit will issue a Traffic Advisory (TA). TAs are indicated on the Avidyne MFD display and aural "Traffic, Traffic" warnings are announced in the headphones and cabin speaker.

According to maintenance records for the Cirrus, the Skywatch was removed, sent in for a "VIP [Verbal Intruder Positioning] upgrade" and reinstalled on September 17, 2007. According to L-3 Avionics personnel, the upgrade provided an extended audio callout capability. In addition to the "Traffic, Traffic" aural warning, the upgraded unit announced the relative bearing, relative altitude and distance of the intruder aircraft. The Skywatch was wired so that it turned on whenever power was applied to the airplane's avionics non-essential bus. There was a circuit breaker in the line, and the pilot could turn off the unit by pulling the circuit breaker. The antenna for the Skywatch was installed on top of the fuselage.

At 1254, the reported weather conditions at RKS were wind variable at 4 knots; visibility 10 miles, clear skies; temperature 23 degrees Celsius (C); dew point 5 degrees C; and altimeter setting 30.23 inches of mercury.

The wreckage of the two airplanes was intermingled and scattered over an area of about 1,400 feet by 1,500 feet. Both wings and the engine separated from the Cessna fuselage. The wing section separated from the Cirrus fuselage, and the fuselage and wing were fragmented. The largest piece of the Cirrus was the engine, firewall, and a portion of the instrument panel. This large piece and the majority of the wing pieces of the Cirrus came to rest near the eastern edge of the debris field. The Cessna fuselage and left wing came to rest near the western edge of the debris field.

Two sets of transfer marks indicative of the collision geometry were identified. The first was an indentation to the left passenger door of the Cessna. A small piece of fiberglass from the Cirrus was caught in a tear in the center of the indentation. Examination of the fiberglass revealed that the painted side had paint protective tape applied consistent with the protective tape used on wheel pant fairings, flaps and other areas of the Cirrus. A square-sided impact mark extended out of the indentation upwards at roughly a 45-degree angle towards the upper door hinge of the Cessna. When the right main landing gear leg of the Cirrus was laid in the square sided impact mark, it conformed to the dimensions of the impact mark.

The second set of transfer marks noted were scratch marks on the wing surfaces. The top inboard skin of the Cessna's left wing exhibited scratches at a 30- to 35-degree angle starting at the leading edge and extending inboard toward the fuselage. A piece of the lower inboard skin from the right wing of the Cirrus had scratches at an approximate 50-degree angle extending from the leading edge aft towards the main landing gear well. When the lower wing skin of the Cirrus was laid atop the upper wing skin of the Cessna, the resultant angle of the two airplane's wings was consistent with the collision angle depicted in the radar data.

Autopsies of the Cessna pilot and the Cirrus pilot and passenger were conducted by Wyoming Pathology, Inc., Laramie, Wyoming. The cause of death for all three individuals was reported as massive trauma. Toxicology tests for drugs and volatiles were performed by the FAA's Toxicology and Accident Research Laboratory. For the Cessna pilot, no drugs were detected and ethanol was detected at 40 mg/dL in muscle; however, the report noted that the ethanol was from sources other than ingestion. For the Cirrus pilot, quinine was detected in lung and ethanol was detected at 18 mg/dL in lung and 64 mg/dL in muscle; however, the report noted the sample was putrefied. Testing for carbon monoxide and cyanide were not performed.

The Avidyne MFD and PFD were examined in order to extract any data recorded regarding the accident flight. Data was recovered from both units. The Cockpit Displays Factual Report in the public docket for this accident contains plots utilizing the data from the units. The plot showing the last 3 minutes of data from the PFD indicates that no abrupt maneuvers took place prior to the collision.

The Garmin GNS430 radios were examined in order to determine the last tuned communication (com) radio frequencies. The upper (#1) radio had an active com frequency of 122.8 and a standby com frequency of 118.375. The lower (#2) radio had an active com frequency of 124.35 and a standby com frequency of 128.35.

The common traffic advisory frequency for the Rock Springs Airport was 122.8, and frequency for the Rock Springs Automated Surface Observation Station was 118.375. The frequency for Salt Lake Center sector 5 was 124.35, and the frequency for sector 8 (the sector immediately prior to sector 5) was 128.35.

The Garmin GMA340 audio panel was examined to determine which of the GNS430 radios were selected at the time of the accident. This effort was unsuccessful.

The Honeywell KGP 560 TAWS unit was examined to determine if it had recorded any data regarding the accident flight. It was determined that the unit did not record the accident flight due to the abnormal shutdown of the unit. According to Honeywell, unless the unit issues a terrain warning during a flight, no data is recorded until a normal shutdown is completed.

The L-3 Avionics SkyWatch unit was examined to determine if it had recorded any data regarding the accident flight. The unit had sustained severe impact damage. Its non volatile memory chip was removed and installed into a test unit in order to read the contents. When the test unit was powered up, a "Check Configuration" error was generated at a system run time of 349 hours 57 minutes. The configuration error was due to differences in configuration between the test bench setup and the installation in the airplane. The last error recorded prior to the test was a "Barometric Altitude Input" error approximately 115 hours prior to the accident (system run time 234 hours 50 minutes). No errors were logged during the accident flight. The unit does not record TAs.

Representatives of L-3 Avionics stated that based on the radar data, the Skywatch would have generated a TA starting about 30 seconds before and continuing until impact. An aural "Traffic, Traffic" warning including the Cessna's relative bearing, relative altitude and distance would have been given once, at the beginning of the TA. A traffic alert message would have been displayed on the MFD in the message bar. The pilot could then have pressed the ACK button next to the message acknowledging the traffic alert and displaying the dedicated traffic page.

Regarding the potential for line of sight blockage due to the location of the Skywatch antenna on top of the Cirrus and the transponder antenna on the bottom of the Cessna, an L-3 Avionics representative stated that "there is always the potential for line of sight blockages by aircraft fuselages." The representative further stated that "due to the geometries of the aircraft, antenna shielding is a possibility," but it cannot be confirmed.

Air Traffic Control Information

Review of an air traffic control radar and audio replay of the accident showed that the sector 5 controller was presented with a conflict alert (flashing symbols on his radar screen) between the Cirrus and the Cessna beginning at 1220:55 and ending at 1223:07.

The sector 5 controller was interviewed and provided the following information. The controller first became aware of the Cirrus when he took the handoff from sector 8. At the time, the Cirrus was approximately 20 miles north of the boundary between sector 8 and sector 5. After taking the handoff, the controller continued working other traffic. The first time he talked to the pilot of the Cirrus was when the pilot requested a lower altitude just as the airplane was entering sector 5. He issued the pilot a descent, instructed the pilot to get the weather information for the airport, advised the pilot to expect a visual approach and issued the altimeter setting.

There were numerous visual flight rules (VFR) targets in the vicinity of Rock Springs. When the Cirrus was about 17 miles northwest of Rock Springs, the controller told the pilot to report the airport in sight. The pilot did so, and was cleared for a visual approach. The controller issued a traffic advisory on the multiple VFR targets in the area and then instructed the pilot to switch to advisory frequency. The pilot responded by asking which runway was in use. The controller advised the pilot that he did not know which runway was in use, and issued the wind at Rock Springs. He also issued a further traffic advisory on a VFR aircraft (the Cessna) that was operating northwest of the airport. Initially, the controller believed that the aircraft was going to be landing at Rock Springs. However, he noticed that the aircraft began tracking toward the northeast, away from the airport.

The controller stated that he knew from previous experience and training that Cirrus aircraft are frequently equipped with a traffic avoidance system. He thought that if he gave the pilot a good position on the conflicting traffic, the pilot would be able to see it using his internal system and avoid the other aircraft. These extended discussions with the pilot caused the controller to get behind on some of his other work, and he needed to catch up with other tasks after he finished talking to the Cirrus. Asked when he first saw the conflict alert between the Cirrus and the other aircraft, the controller stated that he was not sure where the aircraft was when the conflict alert activated. He said that based on his observation of the position of the two aircraft, activation of the conflict alert would have been expected. He believed that providing traffic information to the pilot of the Cirrus and allowing the pilot to switch to the advisory frequency would assist in the resolution of the possible conflict because both pilots would then be on the same frequency.

Initially, the controller stated that he was unable to recall the last time he saw the Cirrus, but that it had looked like the VFR aircraft would pass behind. He later stated that the last time he saw the Cirrus, it looked like the VFR aircraft was "right on him," but it was too late to do anything. Asked when he believed the Cirrus left the center frequency, the controller replied that he believed it occurred right after he made the second traffic call. The pilot had made a remark about targets after the traffic call, but the controller thought the pilot was simply acknowledging the information about the multiple aircraft ahead. Asked whether he continued to scan the track of the Cirrus during the 90-second period that the conflict alert was active before the collision, the controller stated that he was going back and forth between monitoring the Cirrus and other tasks that he needed to perform. At no time did he see anything that made him think he needed to reestablish contact with the aircraft. He also stated that in his experience, attempting to recontact an aircraft after approving a frequency change to advisory frequency was usually futile. The aircraft do not respond. Later in the interview, the controller stated that he was not specifically aware that Cirrus aircraft typically are equipped with two radios.

For further air traffic control information, see the Air Traffic Control Factual Report in the public docket for this accident.