F-16 Main Wreckage Photo NTSB
NTSB Identification: ERA15MA259A
HISTORY OF FLIGHT
On July 7, 2015, about 1101 eastern daylight time, a Cessna 150M, N3601V, and a Lockheed Martin F-16CM, operated by the US Air Force (USAF), collided in midair near Moncks Corner, South Carolina. The private pilot and passenger aboard the Cessna died, and the Cessna was destroyed during the collision. The damaged F-16 continued to fly for about 2 1/2 minutes, during which the pilot activated the airplane’s ejection system. The F-16 pilot landed safely using a parachute and incurred minor injuries, and the F-16 was destroyed after its subsequent collision with terrain and postimpact fire. Visual meteorological conditions prevailed at the time of the accident. No flight plan was filed for the Cessna, which departed from Berkeley County Airport (MKS), Moncks Corner, South Carolina, about 1057, and was destined for Grand Strand Airport, North Myrtle Beach, South Carolina. The personal flight was conducted under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The F-16 was operating on an instrument flight rules (IFR) flight plan and had departed from Shaw Air Force Base (SSC), Sumter, South Carolina, about 1020.
Air Force F-16
According to the USAF, the F-16 pilot was assigned as pilot-in-command for a single-ship, operational check flight to verify the completion of recent corrective maintenance. The flight itinerary included practice instrument approaches at Myrtle Beach International Airport (MYR), South Carolina, and Charleston Air Force Base/International Airport (CHS), Charleston, South Carolina, before returning to SSC. Since the flight was single ship and single pilot, the pilot performed an individual flight briefing using the personal briefing guide. (The Shaw General Briefing Guide is a local USAF document that F-16 pilots use to prepare for their missions.) Before departure, squadron personnel briefed the pilot on a range of subjects, including parking location, maintenance issues, aircraft configuration, notices to airmen, weather, and the mission timeline.
After departing from SSC, the F-16 proceeded to MYR, where the pilot conducted two practice instrument approaches before continuing to CHS. According to air traffic control (ATC) radar and voice communication data provided by the Federal Aviation Administration (FAA), the F-16 pilot contacted the approach controller at CHS about 1052 and requested to perform a practice tactical air navigation system (TACAN) instrument approach to runway 15. The controller instructed the F-16 pilot to fly a heading of 260º to intercept the final approach course. About 1055, the controller instructed the F-16 pilot to descend from 6,000 ft to 1,600 ft. About that time, the F-16 was located about 34 nautical miles (nm) northeast of CHS.
Recorded airport surveillance video showed that the Cessna, which was based at MKS, departed from runway 23. At 1057:41, a radar target displaying a visual flight rules (VFR) transponder code of 1200, and later correlated to be the accident Cessna, appeared in the vicinity of the departure end of runway 23 at MKS at an indicated altitude of 200 ft. The Cessna continued its climb and began tracking generally southeast over the next 3 minutes. For the duration of the flight, the pilot of the Cessna did not contact any ATC facilities, nor was he required to do so.
The CHS automated radar terminal system (ARTS IIE) detected a conflict between the F-16 and the Cessna at 1059:59. According to recorded radar data, the conflict alert (CA) was presented on the radar display and aurally alarmed at 1100:13, when the F-16 and the Cessna were separated laterally by 3.5 nm and vertically by 400 ft.
At 1100:16, the CHS approach controller issued a traffic advisory advising the F-16 pilot of “traffic 12 o’clock, 2 miles, opposite direction, 1,200 [ft altitude] indicated, type unknown.” At 1100:24, the F-16 pilot responded that he was “looking” for the traffic. At 1100:26, the controller advised the F-16 pilot, “turn left heading 180 if you don’t have that traffic in sight.” At 1100:30, the pilot asked, “confirm 2 miles?” At 1100:33, the controller stated, “if you don’t have that traffic in sight turn left heading 180 immediately.” As the controller was stating the instruction and over the next 18 seconds, the radar-derived ground track of the F-16 began turning southerly toward the designated heading.
At 1100:49, the radar target of the F-16 was 1/2 nm northeast of the Cessna, at an altitude of 1,500 ft, and was on an approximate track of 215º. At that time, the Cessna reported an altitude of 1,400 ft and was established on an approximate ground track of 110º. At 1100:53, the controller advised the F-16 pilot, “traffic passing below you one thousand four hundred [ft].” At 1100:54, the altitude of the F-16 remained at 1,500 ft, and the last radar return was received from the Cessna. Recorded radar data indicated that the ARTS IIE continued to provide a CA to the controller until 1101:00. The next radar target for the F-16 was not received until 1101:13. At 1101:19, the F-16 pilot transmitted a distress call, and no subsequent intelligible transmissions were received.
Several witnesses observed both airplanes in the moments leading up to the collision. One witness, located adjacent to the west branch of the Cooper River, noticed the Cessna flying overhead, roughly from west to east, and then observed the F-16 flying overhead, roughly from north to south. He estimated that the two airplanes collided at an altitude of about 900 ft. He further described that both airplanes were “very low.” The F-16 struck the left side of the Cessna, and debris began falling. He reported that a large black cloud of smoke appeared after the collision but did not observe any fire. He stated that neither airplane appeared to conduct any evasive maneuvers before the collision. After the collision, the F-16 then “powered up,” turned right, and flew southbound along the river.
Another witness reported that he was standing in his backyard overlooking the river. He watched as the Cessna flew by from west to east. He next saw the F-16 flying toward the Cessna, coming from the Cessna’s left rear position, roughly north to south. When the F-16 collided with the left side of the Cessna, debris started falling, with some landing in his yard. He stated that it looked as if the F-16 tried to “pull up” just before impact. After the impact, the F-16 turned right and flew along the river to the south and out of sight. Once the F-16 was out of sight, he heard several loud “bang” noises.
ATC radar continued to track the F-16 as it proceeded on a southerly course. After it descended to 300 ft, radar contact was lost at 1103:17 in the vicinity of the F-16 crash site. The F-16 pilot used the airplane’s emergency escape system (ejection seat) to egress, incurring minor injuries as he landed on the ground under canopy. He was subsequently met by first responders. Figure 1 shows the calculated flight track for the F-16 and the Cessna.
See NTSB MoncksCorner Accident Video
According to USAF personnel, the pilot of the F-16 was current and qualified in the accident airplane as a four-ship flight lead. His additional duties at the time of the accident included the position of 55th Fighter Squadron Chief of Mobility. At the time of the accident, he had accumulated 2,383 total hours of military flight experience, including 624 hours in the F-16. The pilot’s total flight experience included 1,055 hours at the controls of the MQ-1B (Predator) and 456 hours at the controls of the MQ-9 (Reaper), both unmanned aerial vehicles. (The remaining hours were in USAF training aircraft and flight simulators.) His recent experience included 35 hours in the 90 days before the accident and 24 hours in the 30 days before the accident, all in the F-16. The USAF reported that the pilot was medically qualified for flight duty and was wearing contact lenses at the time of the accident.
The F-16 pilot’s most recent instrument checkride was completed on August 25, 2014, and his most recent mission (tactical) checkride was completed on March 24, 2015. According to USAF records, none of the pilot’s post-pilot training checkrides contained discrepancies or downgrades.
The F-16 pilot reported during a postaccident interview that he had accumulated about 50 hours of civilian flying experience and possessed an FAA-issued commercial pilot certificate obtained through 14 CFR 61.73. He had not flown civilian aircraft since he began initial USAF pilot training in July 2005.
The pilot of the Cessna held a private pilot certificate with a rating for airplane single-engine land issued on December 29, 2014. His most recent, and only, FAA third-class medical certificate was issued on February 7, 2013, with no waivers or limitations. The pilot’s personal flight logbook was recovered from the wreckage and contained detailed entries between May 2012 and July 5, 2015. As of the final entry, the pilot had accumulated 244 total flight hours, of which 239 hours were in the accident airplane make and model. He had flown 58 hours in the 90 days before the accident and 18 hours in the 30 days before the accident. Review of FAA records revealed no history of accidents, incidents, violations, or pending investigations.
The Cessna pilot’s primary flight instructor indicated in a postaccident interview that the pilot was “very careful” and “responsive.” He stated that the pilot “enjoyed” talking to ATC and was aware of the benefits. During his instruction, he would contact ATC for flight-following without being prompted. A review of the pilot’s logbook revealed that he communicated with SSC ATC on at least 9 occasions and CHS ATC at least 21 times.
Air Traffic Controller
The CHS approach controller was hired by the FAA in August 2006 and attended the FAA academy in Oklahoma City before working at the Oakland Air Route Traffic Control Center. She resigned from the FAA in September 2007 and was rehired in February 2008. She worked at CHS since her rehire. Before working for the FAA, she served as an air traffic controller in the USAF from 1998 to 2000.
The controller was qualified and current on all operating positions at CHS and held no other FAA certifications. Her most recent FAA second-class medical certificate was issued on May 21, 2014, with a requirement to wear glasses while providing ATC services. She was wearing glasses on the day of the accident.
On the day of the accident, the controller was working a regularly scheduled 0700 to 1500 shift. At the time of the accident, she was working the radar west position combined with the radar east position, which was the normal radar configuration at CHS. The radar assistant position, called radar handoff, was also staffed. About 1101, when the accident occurred, she had been working the radar west position for about 1 1/2 hours.
The white- and red-colored Cessna 150M was a single-engine, high-wing airplane with a conventional tail. It was equipped with a rotating beacon light, anticollision strobe lights, navigation position lights, and a landing light. The operational status of each lighting system at the time of the accident could not be determined. Review of the airplane’s maintenance and airworthiness records revealed no evidence that any supplemental equipment, such as high intensity anticollision lights, had been installed after delivery to enhance its visual conspicuity. The airplane was not equipped with a traffic advisory system (TAS), traffic alert and collision avoidance system (TCAS), or automatic dependent surveillance-broadcast (ADS-B) equipment or displays.
The Cessna was equipped with a King KX 155 single VHF communication radio, a King KT 78 mode C transponder, and an Ameri-King AK-350 altitude encoder. Review of maintenance records revealed that the most recent transponder and encoder tests per the requirements of 14 CFR 91.413 were completed on September 8, 2008. On July 20, 2012, an overhauled transponder and new altitude encoder of the same makes and models were installed. The units were ground tested in accordance with the procedures outlined in their respective maintenance manuals, but the maintenance records did not note any tests in accordance with 14 CFR 91.413. The pitot/static system was most recently tested per the requirements of 14 CFR 91.411 on April 11, 2013. The Cessna’s most recent annual inspection was completed on October 14, 2014. At the time of the inspection, the airframe had accumulated 3,651 total hours of operation.
Air Force F-16
The gray-colored F-16 was a single-seat, turbofan-powered fighter airplane. Its most recent 400 hour phase inspection was completed on June 4, 2014, and it had accumulated 237 flight hours since that time. After a flight on June 11, 2015, USAF maintenance personnel completed work on the airplane’s flight control system and subsequently cleared the airplane to return to service on July 2, 2015. At the time of the accident, the airframe had accumulated 4,435 total hours of operation. The airplane was not equipped with a TAS, TCAS, or ADS-B equipment or displays.
The USAF provided general information about the limitations of the F-16 radar and “identification friend or foe” (IFF) systems (more specific information is sensitive). The F-16 was equipped with a radar unit installed in the nose of the airplane that the pilot could use to locate and “lock on” to other aircraft. The radar was forward looking and limited to a search area spanning 120º directly in front of the F-16 (60º either side of center). The radar was also limited by the size of the target and was normally used to identify targets within a 40-mile range, but other settings were available. According to USAF personnel, the radar unit was designed to acquire fast moving enemy aircraft (not slow-moving, small aircraft). USAF personnel did not believe the radar would locate a small general aviation aircraft at takeoff or climb speed. The radar acquired targets by direct energy return off the target aircraft’s surface and used aircraft closure rate rather than the airspeed of the other aircraft to filter out slow-moving targets.
When operating in search target acquisition mode, traffic was displayed as a small, white square target on the radar’s multifunction displays (MFD), which were located on the cockpit instrument panel, near the pilot’s knees. If a target existed, a subsequent sweep of the radar would reveal a new target, and the previous image would be lighter in intensity. There were no aural alerts if a new target appeared. The pilot could place a cursor over the target and “lock” the target on the radar if he/she chose. After locking on, the pilot could obtain the mean sea level (msl) altitude of the target.
The F-16 was also equipped with an IFF interrogator. Targets identified by this system would be displayed on the MFD, but it was not an integral part of the radar. The IFF interrogator could be programmed to request specific types of responses (1 to 4); most civilian aircraft with an operating ATC transponder would provide a “type 3” response. To receive any type of response, the F-16 pilot would have to manually initiate the interrogation process, which takes about 8 to 10 seconds to sweep and display all four types of responses, each being displayed for about 2 seconds.
The F-16 was equipped with a basic autopilot providing attitude hold, heading select, and steering select in the roll axis, and attitude hold and altitude hold in the pitch axis. There was no capability for autopilot-coupled instrument approaches. There were three bank settings: go-to heading, selected steer point, and hold bank angle. While the autopilot was engaged in heading select mode and a new heading was selected, the airplane would turn at about a bank angle not to exceed 30º. According to the F-16 flight manual, the autopilot was able to maintain altitude within ±100 ft under normal cruise conditions. Manual inputs through the control stick would override autopilot functions. If specific limits were exceeded during manual override, the autopilot would disconnect.
The area forecast that included eastern South Carolina was issued at 0445 and forecasted scattered clouds between 3,000 and 4,000 ft msl, with scattered cirrus clouds and widely scattered light rain showers and thunderstorms after 1100.
The closest facility disseminating a terminal aerodrome forecast was CHS. The last forecast published before the accident was issued at 0723. The forecast weather conditions beginning at 0800 and continuing through 1300 included variable winds at 4 knots, greater than 6 statute miles visibility, and few clouds at 4,000 ft above ground level (agl).
Review of weather radar imagery showed no precipitation in the vicinity of the accident site about the time of the accident.
The weather conditions reported at MKS at 1055 included calm wind, 10 statute miles visibility, scattered clouds at 2,600 ft agl, a temperature of 30º C, a dew point of 22º C, and an altimeter setting of 30.15 inches of mercury.
The weather conditions reported at CHS at 1055 included wind from 220º true at 7 knots, 10 statute miles visibility, scattered clouds at 4,000 ft agl, a temperature of 30º C, a dew point of 22º C, and an altimeter setting of 30.15 inches of mercury.
At the time of the accident, the sun was about 57º above the horizon at an azimuth of about 99º.
CHS has two intersecting runways oriented in a 15/33 and 03/21 configuration, at an elevation of 46 ft. The airport is served by numerous instrument approaches, including a VOR [very high omnidirectional range]/DME [distance measuring equipment] or TACAN approach to runway 15. The minimum altitude for the intermediate portion of the approach was 1,600 ft msl, while the minimum crossing altitude at the final approach fix, located 2.8 nm from the runway 15 threshold, was 1,100 ft msl.
ATC services at the airport are provided continuously by a combined ATC tower and terminal radar approach control (TRACON) facility. The CHS TRACON airspace extends for an approximate 40-nm radius from CHS, from the surface to 10,000 ft msl. Radar data are displayed to air traffic controllers at CHS via the ARTS IIE, with the radar feed from the airport surveillance radar (ASR-9), located at CHS.
The airport is surrounded by class C airspace, defined as that airspace extending from the surface up to and including 4,000 ft msl, within a 5-nm radius of CHS and that airspace extending from 1,200 ft msl up to and including 4,000 ft msl, within a 10-mile radius of CHS. There is no specific pilot certification required to operate within the class C airspace, but, according to 14 CFR 91.215, aircraft are required to be equipped with a two-way radio with an operable radar beacon transponder with automatic altitude reporting equipment. According to 14 CFR 91.130, before entering the class C airspace, two-way radio communication must be established and subsequently maintained with the ATC facility providing services.
Pilots requesting ATC services at CHS are required to contact the ATC facility on the publicized radio frequency and provide their position, altitude, radar beacon code, destination, and the nature of their request. Radio contact should be initiated far enough from the class C airspace boundary to preclude entering class C airspace before two-way radio communications are established. Beyond the class C airspace is an outer area that extends to a 20-nm radius of the airport. There were no specific communications or transponder requirements to operate in this area; however, approach control services could still be provided by ATC when operating in the outer area.
MKS, the Cessna’s departure airport, is located about 17 nm north of CHS and is outside the CHS class C airspace. The airspace surrounding MKS and encompassing the collision location is designated as class E and extends from 700 ft agl to 17,999 ft msl. There are no two-way radio communication or transponder use requirements for operation in class E airspace. The established minimum vectoring altitude for ATC in this area is 1,600 ft, which represented the lowest altitude available to controllers when providing radar vectors to aircraft operating under IFR. Figure 2 shows an FAA sectional chart depicting CHS and class C airspace, MKS, and the approximate collision location.
An instrument military training route (MTR), IR-18, transits generally south to north with an altitude structure of 5,000 to 7,000 ft msl, and is located about 1 nm east of MKS. A visual MTR, VR-1040/1041, transits generally east to west with an altitude structure of 200 to 1,500 ft agl and is located about 5 nm northwest of MKS. (The F-16 was not operating on either of these MTRs.) Several military operations areas, two USAF airbases, and a National Guard airbase are located within 60 nm of MKS. The airport/facility directory entry for MKS did not provide any warning or cautions regarding low altitude, high speed military air traffic in the vicinity of the airport.
A crash-survivable memory unit (CSMU) was recovered from the wreckage of the F-16, and the digital flight control system seat data recorder was recovered from the airplane’s ejection seat. Both memory units were forwarded to the airframe manufacturer for data extraction under the supervision of a National Transportation Safety Board (NTSB) vehicle recorder specialist. The data were downloaded normally with no anomalies noted.
WRECKAGE AND IMPACT INFORMATION
The wreckage of the Cessna was recovered in the vicinity of its last observed radar target, over the west branch of the Cooper River. Components from both airplanes were spread over an area to the north and west of that point, extending for about 1,200 ft. The largest portions of the Cessna’s airframe included a relatively intact portion of the fuselage aft of the main landing gear and the separate left and right wings, all of which were within 500 ft northwest of the airplane’s final radar-observed position. Portions of the cabin interior, instrument panel, fuel system, and engine firewall were found distributed throughout the site. The engine, propeller, and nose landing gear assembly were not recovered. The lower aft engine cowling of the F-16 was also recovered in the immediate vicinity of the Cessna’s aft fuselage, while the F-16’s engine augmenter was recovered about 1,500 ft southwest. Small pieces of the F-16’s airframe were also distributed throughout the accident site.
Both of the Cessna’s wings displayed uniform leading-edge crush damage throughout their spans that was oriented aft and upward. Paint transfer and rub markings (consistent with paint from the F-16) oriented from left to right were observed along the upper forward surfaces of both wings. Both fuel tanks were ruptured, and evidence of heat damage and thermal paint blistering were observed on the upper surface of the right wing. Flight control continuity was traced through overload-type cable separations from the cabin area to each flight control surface. Measurement of the pitch trim actuator showed a position consistent with a 3º-to-4º deflection of the tab in the nose down direction, and measurement of the flap actuator showed a position consistent with the flaps having been in the retracted position.
Cessna 150M Main Wreckage Photo NTSB
Air Force F-16
The F-16 wreckage site was located about 6 nm south of the Cessna wreckage site. The F-16 wreckage path was about 700 ft long and oriented roughly 215º, with portions of the airframe distributed along the wreckage path. The wreckage displayed significant ground impact and postimpact fire-related damage.
F-16 Main Wreckage Photo NTSB
MEDICAL AND PATHOLOGICAL INFORMATION
The Department of Pathology and Lab Medicine, Medical University of South Carolina, determined that the cause of death for both occupants of the Cessna was “blunt trauma.” The FAA’s Civil Aerospace Medical Institute performed postaccident toxicological testing on tissue specimens from the Cessna pilot. The specimens tested negative for a wide range of drugs, including major drugs of abuse. Although the specimens tested positive for ethanol, the levels of ethanol were consistent with postmortem ethanol production.
A Department of Defense Armed Forces medical examiner scientist performed postaccident toxicological testing on blood and urine specimens from the F-16 pilot, and the specimens tested negative for carbon monoxide, ethanol, and major drugs of abuse.
TESTS AND RESEARCH
Aircraft Performance and Cockpit Visibility Study
The NTSB’s investigation examined the ability of the Cessna and F-16 pilots to see and avoid the other aircraft. To determine approximately how each aircraft would appear in the pilots’ fields of view, the position of the “target” aircraft in a reference frame attached to the “viewing” aircraft must be calculated. This calculation depends on the positions and orientation (pitch, roll, and yaw angles) of each aircraft, as well as the location of the pilots’ eyes relative to the cockpit windows. Data for the F-16 were derived from its CSMU, while orientation information for the Cessna was estimated based on an analysis of the radar data.
After the position and orientation of each airplane were determined, the position of each airplane in the body axis system of the other was calculated. These relative positions then determined where the “target” airplanes likely would have appeared in the fields of vision of the pilots of the “viewing” airplanes. The study assumed a nominal pilot seating (and eye) position in each cockpit and evaluated a matrix of eye displacements from the nominal eye position. For this study, the relative positions of the two airplanes were calculated beginning when the Cessna became visible on radar and then at 1-second intervals up to the collision. The time, location, and altitude of the collision were determined based on extrapolation of the radar and F-16 CSMU data and on the location of the main Cessna wreckage. The locations of the structures and transparencies of the F-16 and Cessna in the pilots’ fields of view were determined from the interior and exterior dimensions of representative airplanes, as measured using a laser scanner. The structural obscurations to each pilot’s view were merged with the calculated relative position data and are discussed below. The variations in eye position changed the timing of the obscurations of the opposite aircraft by less than +/-1.5 seconds at any given point.
At 1100:16, when the controller provided the initial traffic advisory to the F-16 pilot, the F-16 was in a wings-level attitude, at an altitude of about 1,570 ft, on a ground track of 252º, and at a ground speed of 253 knots. The Cessna’s calculated position was 3.25 nm from the F-16, at a position directly ahead (about 12 o’clock), and at an altitude of roughly 1,200 ft. The Cessna’s ground track was 109º, and it was climbing at a rate of about 240 ft per minute. The aircraft performance and cockpit visibility study showed that, at 1100:18, the Cessna would have appeared to the F-16 pilot as a very small, stationary object just above the horizon and near the center of the airplane’s heads up display (HUD); the F-16 would have appeared to the Cessna pilot as a small, stationary object just above the horizon, but outside of the left cockpit door window, near the forward vertical post of the door frame.
At 1100:26, when the controller advised the F-16 pilot, “turn left heading 180 if you don’t have that traffic in sight,” the relative positions changed slightly, with the Cessna moving slightly to the left but still remaining within the F-16’s HUD, and the F-16 moving slightly aft in the Cessna pilot’s left window.
At 1100:33, when the controller stated, “If you don’t have that traffic in sight turn left heading 180 immediately” and as the F-16 began banking to the left, the F-16 pilot’s view of the Cessna would have been obscured behind the left structural frame of the HUD. The position of the F-16 would have remained unchanged to the Cessna pilot.
At 1100:49, as the F-16 was executing its left turn at a bank angle of 30º, the Cessna would have become more discernable in the lower right portion of the F 16 pilot’s HUD (see figure 4a). The F-16 would also have become more discernable, visible through the Cessna pilot’s left window at a point just forward of the wing strut attachment point.
At 1100:53, when the controller advised the F-16 pilot, “traffic passing below you” at 1,400 ft, the F-16 was flying at an altitude of 1,480 ft, while the estimated altitude of the Cessna was 1,440 ft. The closure rate of both airplanes at this point was 264 knots. The Cessna would have been visible to the right of the structural frame of the F 16’s HUD, while the F-16 would have appeared to the Cessna pilot in largely the same position but with a more defined shape.
Over the next 3 seconds, the airplanes continued to approach each other, with the F-16 approaching the Cessna from its left and slightly above. The Cessna would have been completely obscured by the lower right cockpit structure of the F-16, as the airplane banked in its turn to the left. The F 16 would have become partially obscured by the left wing strut.
See NTSB Moncks Corner F 16 Visibility Video
See NTSB Moncks Corner C150 Visibility Video
ORGANIZATIONAL AND MANAGEMENT INFORMATION
USAF Mid-Air Collision Avoidance Program
The USAF has a Mid-Air Collision Avoidance (MACA) program detailed in Air Force Instruction (AFI) 91-202, dated June 24, 2015. According to AFI 91-202, USAF flying units must have a written MACA program, and the unit safety office is responsible for its creation, documentation, and upkeep. The 20th Fighter Wing (FW) Safety Office administered the Shaw Air Force Base MACA program. The required elements are a MACA pamphlet and a poster, primarily designed for use in the civilian community. The program includes civilian outreach and incorporates interaction with pilot advocacy organizations, the FAA, local airports, and fixed base operators. The 20th FW Safety Office also maintains a public website populated with the MACA program products and other safety information. According to 20th FW Safety Office personnel, activities related to MACA are coordinated with two other military bases: Charleston Joint Base and McEntire Joint National Guard Base. The Charleston Joint Base Flight Safety office held MACA seminars at MKS in June 2012, January 2014, and March 2015.
Members of the USAF Accident Investigation Board interviewed the F-16 pilot after the accident. He reported that he had the radar configured for a 20- and 40-mile range, manually alternating back and forth, and could not recall if his IFF interrogator was set up to receive civilian transponder replies. He was using a scan pattern that included looking outside; checking instruments for altitude, airspeed, and heading; and checking the radar display.
The F-16 pilot indicated that he had acquired and locked on a radar target 20 miles away. He stated that shortly thereafter, the controller issued an alert for traffic at his 12 o’clock position, 2 miles away, at 1,200 ft. He remarked that a 2-mile call was the “…closest call I’ve ever received” and that it was “…a big alert for me.” He then asked the controller to “confirm two miles”; he indicated in a postaccident interview that he asked that question because he was looking at traffic on his radar at 20 miles away. He then began aggressively looking to visually acquire the airplane and recalled a command from the controller to turn left “immediately” to a heading of 180º. He stated that he used the autopilot to execute the turn so that he could continue to search outside for the traffic. The autopilot turn used 30º of bank and standard rate, or 3º per second of turn. He continued to search for the traffic until he observed the Cessna directly in front of his airplane, “within 500 feet.” He then applied full aft control stick inputs to avoid a collision, but it was “too late.” He estimated that the time from initial sighting of the Cessna to the impact was less than 1 second. After the collision, he attempted to maintain control of his airplane; however, once he determined that continued controlled flight was not possible, he initiated his emergency egress.
Air Traffic Controller
The air traffic controller described the traffic on the day of the accident as light and routine, with nothing out of the ordinary. Several USAF fighter aircraft from SSC were making approaches to CHS when the F-16 entered the airspace from the northeast and requested a TACAN approach. The controller told the pilot to expect the requested approach and provided climb-out instructions after completing the approach. She issued a radar vector of 260º to intercept the 10- to 15-mile final approach course for the instrument approach. The intent of this vector was to keep the F-16 south of, and to avoid overflying, MKS. The controller stated that she then directed the F-16 to descend and maintain 1,600 ft and was “pretty much done with him” while she worked other traffic, including a flight of two other F 16s. She had descended the accident airplane to 1,600 ft because that was the minimum vectoring altitude at CHS. She stated that this was her usual technique; getting aircraft to their final altitude quickly allowed her more efficient use of her time.
When the controller initially noticed the Cessna depart from MKS, she thought that it would remain in the local VFR traffic pattern. She described that, generally, pattern traffic at MKS was rare and, when present, typically stayed below 1,000 ft. She then descended the other two aircraft flight of F-16s to sequence them behind the accident F-16 and to get them around other traffic. Shortly after, she asked the two-aircraft flight to expedite its descent to 3,000 ft and noticed that the Cessna was climbing above 1,000 ft. She responded by advising the F-16 pilot, hoping that he would be able to visually acquire the traffic, but the F-16 pilot did not report the traffic in sight. She advised the F-16 pilot to turn left heading 180 if he did not have the traffic in sight.
As the radar targets were continuing to close on one another, she directed the F-16 pilot that if he did not have the traffic in sight to turn left heading 180 immediately. She reported that the 180 heading assignment was preferred over a turn to the north because the turn was quicker, and she believed that “fighters could turn on a dime.” She stated that her expectation was that the word “immediately” meant to react now and that, with a fighter aircraft, it meant to do a “max performance turn” to the heading. She stated that she did not recall seeing or hearing a CA generated by the ATC radar system. The controller indicated in a postaccident interview that she chose not to direct the F 16 to climb because the altitude indicated for the Cessna’s radar target was unconfirmed.
The controller advised the F-16 pilot that the Cessna had passed below him and thought the two aircraft were clear of each other until she saw the Cessna’s radar target disappear followed by the F 16 pilot’s distress call. She briefly initiated a call to the pilot and then turned to the radar handoff controller and told him “I don’t know what to do.” The radar handoff controller advised her to “separate what you’ve got.”
ATC Radar Equipment
The radar display system in use at CHS at the time of this accident, ARTS IIE, is designed to support one or two sensors and up to 22 displays in two different configurations and can process 256 simultaneous tracks per sensor. At the time of the accident, there were no known or reported equipment discrepancies with the ARTS IIE system that would have affected the controller’s ability to provide ATC services.
The ARTS IIE has numerous capabilities and functions to help controllers with strategic and tactical decision-making. One of these functions is the CA/mode C intruder, which provides controllers with visual and immutable aural warnings for aircraft that are or will be in dangerous proximity to one another. A CA provides a visual presentation on the radar scope display associated with the conflicting aircraft and an aural alarm when conditions warrant. These conditions are based on vertical and horizontal parameters established for the environment in which the aircraft are operating. For example, in an en route environment where aircraft are operating at higher altitudes and faster speeds, the parameters would be more sensitive when compared to an airport environment, where aircraft operate closer to each other and at lower speeds. For a predicted alert, the ARTS IIE evaluates a developing conflict for two of three consecutive radar sweeps. The average sweep of an ASR (a 360º scan) takes about 5 seconds.
The CHS ARTS IIE detected the conflict between the F-16 and the Cessna at 1059:59, and the CA was presented on the radar scope with an accompanying aural alert at 1100:13. The ARTS IIE continued to provide a CA to the controller until 1101:00. As the controller stated in her postaccident interview, she did not recall seeing or hearing the CA, but review of archived ATC audio revealed that her initial traffic advisory to the F-16 began at 1100:16, 3 seconds after the CA alerted. A postaccident test of the CA alarm at CHS revealed that it worked properly.
Factors Impacting the Pilots’ Ability to Detect Other Traffic
The collision occurred in a relatively low-density air traffic environment in visual meteorological conditions (VMC). The Cessna was equipped with an operating transponder and single communication radio but was not equipped with any technologies in the cockpit that display or alert of traffic conflicts, such as traffic advisory systems, traffic alert and collision avoidance systems, or automatic dependent surveillance-broadcast systems. The Cessna had departed from a nontowered airport and was still in close proximity to the airport when the collision occurred. The Cessna pilot had not requested or received flight-following services from ATC at the time of the collision, nor was he required to do so. Based on his proximity to the departure airport, it is reasonable to expect that the Cessna pilot likely was monitoring that airport’s common traffic advisory frequency (CTAF) for awareness of airplanes in the vicinity of the airport, as recommended by the FAA’s AIM. Based on statements from the Cessna pilot’s flight instructor and from his logbook entries, which both cited past experience communicating with ATC, it is also reasonable to assume that had the collision not occurred, the pilot likely would have contacted ATC at some point during the flight to request flight-following services.
Due to the Cessna’s lack of technologies in the cockpit that display or alert of traffic conflicts and the pilot’s lack of contact with ATC, his ability to detect other traffic in the area was limited to the see-and-avoid concept. While not required, had the Cessna been equipped with a second communication radio, the pilot could have used it to contact ATC while still monitoring the departure airport’s CTAF. Had the Cessna pilot contacted ATC after departing and received ATC services, the controller would have had verification of the Cessna’s altitude readout and its route of flight, which would have helped her decision-making process. The controller also could have provided the Cessna pilot awareness of the F-16.
The F-16 was operating under IFR in VMC. The F-16 pilot’s ability to detect other traffic was limited to the see-and-avoid concept, supplemented with ATC traffic advisories. While the F-16 pilot could use the airplane’s tactical radar system to enhance his awareness of air traffic, it was designed to acquire fast-moving enemy aircraft rather than slow-moving, small aircraft and was thus unable to effectively detect the Cessna. (The radar system did detect a target 20 miles away, which is likely what led the F-16 pilot to question the location of the traffic that the controller had indicated was 2 miles away.) The F-16 was not otherwise equipped with any technologies in the cockpit that display or alert of traffic conflicts. The F-16 pilot did eventually visually acquire the Cessna but only when the airplanes were within about 430 ft of one another, about 1 second before the accident.
A factor that can affect the visibility of traffic in VMC is sun glare, which can prevent a pilot from detecting another aircraft when it is close to the position of the sun in the sky. For the F-16 pilot, the sun would have been behind and to his left as the airplanes approached one another. Although the Cessna pilot would have been heading toward the sun, the sun’s calculated position would likely have been above a point obstructed by the Cessna’s cabin roof and would not have been visible to the Cessna pilot. Thus, sun glare was not a factor in this accident.
Aircraft Performance and Cockpit Visibility Study
NTSB aircraft performance and cockpit visibility study showed that, as the accident airplanes were on converging courses, they each would have appeared as small, stationary, or slow-moving objects to the pilots. Given the physiological limitations of vision, both pilots would have had difficulty detecting the other airplane. Specifically, the study showed that the Cessna would have appeared as a relatively small object through the F-16’s canopy, slowly moving from the center of the transparent heads-up display (HUD) to the left of the HUD. As the F-16 started the left turn as instructed by the air traffic controller, the Cessna moved back toward the center of the HUD and then off to its right side, where it may have been obscured by the right structural post of the HUD. It was not visible again until about 2 seconds before the collision. (Figures 3a and 5a in the factual report for this accident show the simulated cockpit visibility from the F-16 at 1100:18 and 1100:56, respectively.) The F-16 pilot reported that before the controller alerted him to the presence of traffic, he was actively searching for traffic both visually and using the airplane’s targeting radar. He reported that after the controller advised him of traffic, he was looking “aggressively” to find it. By the time he was able to visually acquire the Cessna, it was too late to avert the collision.
The investigation could not determine to what extent the Cessna pilot was actively conducting a visual scan for other aircraft. Our aircraft performance and cockpit visibility study showed that the F-16 would have remained as a relatively small and slow-moving object out the Cessna’s left window (between the Cessna’s 9 and 10 o’clock positions) until less than 5 seconds before the collision. Given the speed of the F-16, the Cessna pilot likely would not have had adequate time to recognize and avoid the impending collision.
Cockpit Display of Traffic Information
Although the Cessna and F-16 pilots were responsible for seeing and avoiding each other, NTSB aircraft performance and cockpit visibility study showed that, due to the physiological limitations of vision and the relative positions of the airplanes, both pilots would have had difficulty detecting the other airplane. Research indicates that any mechanism to augment and focus pilots’ visual searches can enhance their ability to visually acquire traffic. (AC 90-48D highlights aircraft systems and technologies available to improve safety and aid in collision avoidance, and our report regarding a midair collision over the Hudson River [AAR-10/05] states that “traffic advisory systems can provide pilots with additional information to facilitate pilot efforts to maintain awareness of and visual contact with nearby aircraft to reduce the likelihood of a collision. …”) One such method to focus a pilot’s attention and visual scan is through the use of cockpit displays and aural alerts of potential traffic conflicts. Several technologies can provide this type of alerting by passively observing and/or actively querying traffic. While the accident airplanes were not equipped with these types of systems, their presence in one or both cockpits might have changed the outcome of the event. (The images from our in-cockpit traffic display simulation are representative of the minimum operations specifications contained in RTCA document DO-317B, Minimum Operational Performance Standards for Aircraft Surveillance Applications System [dated June 17, 2014], but do not duplicate the implementation or presentation of any particular operational display exactly; the actual images presented to a pilot depend on the range scale and background graphics selected by the pilot.)
Because the Cessna pilot was not in contact with ATC and was relying solely on the see-and-avoid concept, an indication of approaching traffic might have allowed him to visually acquire the F-16 and take action to avoid it. While most systems are limited to aiding pilots in their visual acquisition of a target and do not provide resolution advisories (specific maneuvering instructions intended to avoid the collision), the augmentation of a pilot’s situational awareness might allow the pilot to change the flightpath in anticipation of a conflict and, thus, avoid airplanes coming in close proximity to one another. The Cessna pilot might have noted the presence of the F-16 and its level altitude of about 1,600 ft as he continued his departure climb. With this information, the Cessna pilot might have arrested his airplane’s climb as he began a visual search, thus creating an additional vertical buffer between his airplane and the approaching F-16.
While the F-16 pilot’s visual search was augmented by the controller’s traffic advisory, a successful outcome would have depended upon the pilot’s visual acquisition of the target airplane in time to take evasive action. Our in-cockpit traffic display simulation showed that the F-16 pilot might have first observed the Cessna when it was about 15 nm away, or nearly 3 minutes before the collision. As the F-16 closed to within 6 nm of the Cessna, or slightly more than 1 minute before the collision, the conflict might have become even more apparent to the pilot showing that not only were the airplanes in close proximity laterally but also that they were only separated vertically by 600 ft. As the F-16 pilot was beginning his left turn as instructed by ATC, the presence of the Cessna would have been aurally annunciated, and its traffic symbol would have changed from a cyan color to a yellow color. The information presented on the in-cockpit traffic display would have clearly indicated that the airplanes were on a collision course that might not be resolved by a left turn and that the vertical separation between the airplanes had decreased to 300 ft.
Consequently, an in-cockpit traffic display could have helped the F-16 pilot recognize the potential for a collision in advance of the controller’s instruction to turn left. The earlier warning also could have provided him additional time to conduct his visual search for the Cessna and potentially take other preemptive action to avoid the collision. Had the F-16 been equipped with a system that was able to provide the pilot with resolution advisories, the F-16 pilot could have taken action in response to that alarm to avoid the collision, even without acquiring the Cessna visually.
POST ACCIDENT ACTIONS
In November 2016, NTSB issued safety recommendations to the FAA and Midwest Air Traffic Control, Robinson Aviation, and Serco (companies that operate federal contract towers) to (1) brief all air traffic controllers and their supervisors on the ATC errors in this midair collision and one that occurred on August 16, 2015, near San Diego, California; and (2) include these midair collisions as examples in instructor-led initial and recurrent training for air traffic controllers on controller judgment, vigilance, and/or safety awareness.
In November 2016, NTSB also issued a safety alert titled “Prevent Midair Collisions: Don’t Depend on Vision Alone” to inform pilots of the benefits of using technologies that provide traffic displays or alerts in the cockpit to help separate safely.(See: NTSB Issues Safety Alert to Pilots on Midair Collision Prevention. November 2016) In May 2015 [revised in December 2015], NTSB issued a safety alert titled “See and Be Seen: Your Life Depends on It” regarding the importance of maintaining adequate visual lookout. (See: See and Be Seen: Your Life Depends on It. NTSB Safety Alert 045 May 2015)
After the accident, the Cessna’s departure airport engaged in several outreach efforts (including posting midair collision avoidance materials locally and having outreach meetings with pilots) to raise awareness regarding midair collisions and encourage contact with ATC. The airport also updated its chart supplement to note the presence of military and other traffic arriving at and departing from CHS.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
- The approach controller’s failure to provide an appropriate resolution to the conflict between the F-16 and the Cessna. Contributing to the accident were the inherent limitations of the see-and-avoid concept, resulting in both pilots’ inability to take evasive action in time to avert the collision.
- NTSB Issues Safety Alert to Pilots on Midair Collision Prevention. November 2016
- See and Be Seen: Your Life Depends on It. NTSB Safety Alert 045 May 2015
By Laura Duque-Arrubla, a medical doctor with postgraduate studies in Aviation Medicine, Human Factors and Aviation Safety. In the aviation field since 1988, Human Factors instructor since 1994. Follow me on facebook Living Safely with Human Error and twitter@dralaurita. Human Factors information almost every day