ERA15MA259

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.

The pilot of the F-16, who was operating on an instrument flight rules (IFR) flight plan, was in contact with air traffic control (ATC) and was provided radar vectors for a practice instrument approach to Charleston Air Force Base/International Airport (CHS), Charleston, South Carolina; the F-16 descended to an altitude of about 1,600 ft mean sea level as instructed by the air traffic controller. Shortly thereafter, the Cessna departed under visual flight rules (VFR) from a nearby nontowered airport; the Cessna pilot was not in contact with ATC, nor was he required to be, and had not requested traffic advisory (flight-following) services. As the Cessna continued its departure climb, the airplanes converged to within about 3.5 nautical miles (nm) laterally and 400 ft vertically, triggering a conflict alert (CA) on the controller's radar display and an aural alarm. About 3 seconds later, the air traffic controller issued a traffic advisory notifying the F-16 pilot of the position, distance, and indicated altitude of the radar target that corresponded to the Cessna, stating that the aircraft type was unknown. When the F-16 pilot replied that he was looking for the traffic, the controller issued a conditional instruction to the F-16 pilot to turn left if he did not see the airplane. The F-16 pilot did not see the airplane and responded, asking "confirm two miles?" The controller responded, "if you don't have that traffic in sight turn left heading 180 immediately." As the controller began this transmission, the F-16 pilot initiated a standard rate (approximately) left turn using the autopilot so that he could continue to visually search for the traffic; however, the airplanes continued to converge and eventually collided about 40 seconds after the controller's traffic advisory notifying the F-16 pilot of traffic. (Figure 1 in the factual report for this accident shows the calculated flight tracks for the Cessna and F-16.) Air Traffic Controller and F-16 Pilot Performance During postaccident interviews, the controller reported that when she observed the Cessna's target on her radar display as it departed, she thought that the airplane would remain within its local traffic pattern, which was not the case. Therefore, it was not until the airplanes were within about 3.5 nm and 400 vertical ft of one another that the controller notified the F-16 pilot of the presence of the traffic by issuing the traffic advisory, which was about 3 seconds after the ATC radar CA alarmed. (Federal Aviation Administration [FAA] Order 7110.65, Air Traffic Control, paragraph 2-1-21, "Traffic Advisories," states, in part, that a controller should "Unless an aircraft is operating within Class A airspace or omission is requested by the pilot, issue traffic advisories to all aircraft (IFR or VFR) on your frequency when, in your judgment, their proximity may diminish to less than the applicable separation minima. Where no separation minima applies, such as for VFR aircraft outside of Class B/Class C airspace, or a TRSA [terminal radar service area], issue traffic advisories to those aircraft on your frequency when in your judgment their proximity warrants it. …")  When the controller issued the traffic advisory, about 40 seconds before the eventual collision, the F-16 and the Cessna had a closure rate of about 300 knots. If the F-16 pilot had reported the Cessna in sight after the controller's traffic advisory, the controller likely would have directed the F-16 pilot to maintain visual separation, which is a common controller technique to separate aircraft. While the controller tried to ensure separation between the airplanes, her attempt at establishing visual separation at so close a range and with the airplanes converging at such a high rate of speed left few options if visual separation could not be obtained.  The options available to the controller when issuing instructions to the F-16 pilot to avoid the conflict included a turn, climb, some combination thereof, or not issuing an instruction at all. (An instruction to descend was not an option because the F-16 was already at the minimum vectoring altitude for the area.) The controller indicated in a postaccident interview that she chose not to instruct the F-16 to climb because the altitude indicated for the Cessna's radar target was unconfirmed (the Cessna pilot had not contacted ATC). An element informing the controller's decision-making as to which instruction to provide was likely the flow of other traffic into the airport at that time. Arriving aircraft, including the accident F-16, were being sequenced to runway 15 via the final approach course extending from the approach end of the runway. Given the traffic flow, the left turn instruction to the F-16 would have kept the airplane on a heading closer toward, rather than farther from, its destination and would have made returning the F-16 to the intended final approach course much easier. However, the controller's instruction to the F-16 pilot to turn left required the F-16's path to cross in front of the Cessna. Although this decision was not contrary to FAA guidance for air traffic controllers, it was the least conservative decision, as it was most dependent on the F-16 pilot's timely action for its success. Further, the controller issued the instruction to turn left if the F-16 pilot did not have the Cessna in sight. The F-16 pilot responded to the controller's conditional instruction with a question ("confirm two miles?") that indicated confusion about the distance of the traffic. The F-16 pilot's attempt to visually acquire the Cessna per the controller's conditional instruction likely resulted in a slight delay in his beginning the turn. The collision likely would have been avoided had the F-16 pilot initiated the left turn, as ATC instructed, when he realized that he did not have the traffic in sight. About 7 seconds elapsed between the beginning of the controller's first conditional instruction to turn and the beginning of her subsequent conditional instruction to the F-16 pilot to turn "immediately." Analysis of the radio transmission recordings and the F-16's flight recorder data showed that, as the controller was making the subsequent conditional instruction, the F-16 pilot began turning to the left, which pointed his aircraft toward the Cessna. Due to the closure rate, the close proximity of the two airplanes, and human cognitive limitations, the controller did not recover from her ineffective visual separation plan, which placed the airplanes in closer proximity to each other, and switch to an alternative method of separation. The controller's best course of action would have been to instruct the F-16 pilot to turn before the airplanes came into close proximity with each other and preferably in a direction that did not cross in front of the Cessna's path. In postaccident interviews, the controller stated that when she issued the command to the F-16 pilot to turn left "immediately," she expected that the F-16 pilot would perform a high performance maneuver and that she believed that fighter airplanes could "turn on a dime." The FAA's Aeronautical Information Manual (AIM) Pilot-Controller Glossary defines "immediately" as a term used by ATC or pilots "when such action compliance is required to avoid an imminent situation." Further, the AIM states that controllers should use the term "immediately" to "impress urgency of an imminent situation" and that "expeditious compliance by the pilot is expected and necessary for safety." As described above, the F-16 pilot did not meet her expectation that the turn be conducted at a greater-than-standard rate. The controller's expectation of the F-16 pilot's performance was based on her assumption that a fighter airplane would perform a high performance turn to the heading; however, this expectation of performance was not clearly communicated. Based on the controller's instructions and the a

Aircraft 2 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. Cessna 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 Collision 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. Figure 1. Calculated flight track for the F-16 (yellow) and the Cessna (orange). (The first witness is located north of the collision point, and the second witness is located southwest of the collision point.) Cessna 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 surveillanc --- Aircraft 1 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. 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. 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) (see figure 3a); 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 (see figure 3b). Figure 3a. Simulated cockpit visibility from the F-16 at 1100:18, when the airplanes were 3.1 nm apart. (Transparent shadow masks depict areas where visibility is obscured by airplane structure.) Figure 3b. Simulated cockpit visibility from the Cessna at 1100:18, when the airplanes were 3.1 nm apart. (Transparent shadow masks depict areas where visibility is obscured by airplane structure.) 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 (see figure 4b). Figure 4a. Simulated cockpit visibility from the F-16 at 1100:49, when the airplanes were 0.6 nm apart. Figure 4b. Simulated cockpit visibility from the Cessna at 1100:49, when the airplanes were 0.6 nm apart. 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 (see figure 5a). The F 16 would have become partially obscured by the left wing strut (see figure 5b). Figure 5a. Simulated cockpit visibility from the F-16 at 1100:56, when the airplanes were 260 ft apart. Figure 5b. Simulated cockpit visibility from the Cessna at 1100:56, when the airplanes were 260 ft apart. In-Cockpit Traffic Display Simulation The FAA's Aeronautical Information Manual (AIM) (dated December 10, 2015, and revised on May 26, 2016), paragraph 4-5-7, states that ADS B is a surveillance technology deployed throughout the National Airspace System. The ADS-B system is composed of aircraft avionics and a ground infrastructure. Onboard avionics determine the position of an aircraft by using the GPS and transmitting its position along with additional information about the aircraft to ground stations for use by ATC and other ADS-B services. This information is transmitted at a rate of approximately once per second. ADS-B avionics can have the ability to both transmit and receive