When it comes to keeping airplanes from bumping into each other, it still looks as if one of the best things we have going for us is the “big sky” concept. Put simply, there’s such a vast amount of airspace, and aircraft so often fly random routes, that the odds that our aircraft will not be in the same place at the same time as another aircraft are greatly in our favor. The odds go down as traffic density increases, and that’s where controllers, technology and our eyes become increasingly important to help prevent us from hitting each other. As we move deeper into the ADS-B era, which will enable increased traffic density along airways and approach corridors, midair avoidance becomes even more of an issue.
The NTSB turned the spotlight on midairs in a Safety Recommendation Report and separate Safety Alert issued within a few days of each other. A midair that occurred on July 7, 2015, at Moncks Corner, South Carolina, involving a Cessna 150M and a military F-16, was highlighted in both documents. The two people onboard the Cessna died, while the F-16 pilot ejected and received minor injuries. The F-16 was being handled by air traffic control (ATC), while the Cessna wasn’t in contact with any ATC facility, and wasn’t required to be. The Safety Board said that this accident, and others it highlighted, shows the need for better controller training in recognizing impending conflicts and taking positive action to ensure separation.
The Safety Recommendation Report called on the FAA and companies that operate contract towers for the agency to make controllers familiar with what happened in the Moncks Corner and other midair collisions so mistakes made by those controllers won’t be repeated.
The Moncks Corner accident, and three others, appear in the NTSB’s Safety Alert, which urges pilots to make better use of technology to help overcome the shortcomings of eyes and controllers.
In the context of U.S. aviation safety, the number of midairs isn’t staggering. My search of NTSB data for 2015 produced seven midair collisions, two of which involved a total of seven fatalities. For 2016, the result again was seven midairs, with five involving fatalities in which 16 were killed. Perhaps of greater concern is the number of near-midairs reported by pilots to the FAA. In 2015, there were 179 reported, with 123 of them involving a miss of less than 500 feet and a collision being avoided only by evasive action. Naturally, there’s no way to tell how many near-midairs weren’t reported to the FAA, nor how many pilots remained blissfully unaware of the fact that their aircraft was almost hit.
The NTSB said pilots need to educate themselves about the benefits of flying an aircraft equipped with technologies that aid in collision avoidance. These could include ADS-B, a panel-mounted traffic collision avoidance system, or a portable traffic alerting unit.
The Safety Board said technology should be used to separate aircraft before aggressive, evasive maneuvering is required. Without it, said the NTSB, visual acquisition and separation is the primary means of collision avoidance when weather conditions allow.
It was about 11:01 a.m. when the Cessna 150M and a Lockheed Martin F-16CM operated by the U.S. Air Force (USAF) collided. The private pilot and passenger aboard the Cessna were killed, and the Cessna was destroyed. The F-16 pilot was able to eject, descended under the parachute and received only minor injuries.
The Cessna departed from Berkeley County Airport in Moncks Corner (KMKS), and was going to Grand Strand Airport in North Myrtle Beach on a VFR Part 91 personal flight. The F-16 was on an operational check flight after maintenance. It was on an IFR flight plan out of Shaw Air Force Base, Sumter, S.C., and had taken off at about 10:20 a.m.
The flight itinerary included practice instrument approaches at Myrtle Beach International Airport (KMYR) and Charleston Air Force Base/International Airport (KCHS). The pilot conducted two approaches to KMYR, then contacted Charleston Approach at about 10:52 asking for a practice tactical air navigation system (TACAN) instrument approach to Runway 15. The controller instructed him to fly a heading of 260 degrees to intercept the final approach course. About 10:55, the controller instructed the pilot to descend from 6,000 feet to 1,600 feet. About that time, the F-16 was located about 34 nautical miles (nm) northeast of KCHS.
The Cessna 150M was based at KMKS. Airport surveillance video showed it departing from Runway 23. At 10:57:41, radar picked up the Cessna’s transponder squawking 1200 in the vicinity of the departure end of Runway 23 at an indicated altitude of 200 feet. For the next three minutes, the Cessna continued its climb and began tracking generally southeast. The pilot of the Cessna did not contact any ATC facilities, nor was he required to do so.
At 10:59:59, the automated radar terminal system (ARTS IIE) at Charleston detected a conflict between the F-16 and the Cessna. According to recorded radar data, the conflict alert symbol (CA) was presented on the radar display and an audio alarm went off at 11:00:13. The F-16 and the Cessna were separated laterally by 3.5 nm and vertically by 400 feet at that time.
At 11:00:16, the CHS approach controller issued a traffic advisory to the F-16 pilot: “Traffic 12 o’clock, 2 miles, opposite direction, 1,200 [feet altitude] indicated, type unknown.” Investigation determined the F-16 was in a wings-level attitude, at about 1,570 feet, on a ground track of 252 degrees, 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 roughly 1,200 feet. The Cessna’s ground track was 109 degrees, and it was climbing at about 240 feet per minute. The aircraft performance and cockpit visibility study showed that, at 11:00:18, the F-16 pilot would have seen a very small, stationary object just above the horizon and near the center of the airplane’s heads-up display (HUD). The Cessna pilot would have seen the F-16 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 11:00:24, the F-16 pilot replied that he was looking for the traffic. At 11:00:26, the controller advised the F-16 pilot, “Turn left heading 180 if you don’t have that traffic in sight.” At this point, the Cessna moved slightly to the left, but still remained within the F-16’s HUD; the F-16 moved slightly aft in the Cessna pilot’s left window.
At 11:00:30, the pilot asked, “Confirm 2 miles?” At 11:00:33, the controller said, “If you don’t have that traffic in sight turn left heading 180 immediately.” As the controller finished, radar was showing the F-16 slowly beginning to turn toward the south. 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. The turn continued for 18 seconds.
Radar data showed that, at 11:00:49, the F-16 was a half-mile northeast of the Cessna, at 1,500 feet, on a track of about 215 degrees. The Cessna’s transponder was reporting 1,400 feet and radar returns show the airplane was established on a track of about 110 degrees. At 11:00:53, the controller advised the F-16 pilot, “Traffic passing below you one thousand four hundred [feet].” 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 it had been, but with a more defined shape. Over the next three seconds, the F-16 continued 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 remained banked in its turn to the left. The view of the F-16 would have become partially obscured by the Cessna’s left wing strut.
The ARTS IIE radar system continued to show a conflict alert on the controller’s scope until 11:01:00. At 11:01:19, the F-16 pilot transmitted a distress call.
Members of an Air Force accident investigation board interviewed the F-16 pilot. He said 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, two miles away, at 1,200 feet. He said it 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 asked that question because he was looking at the 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 180 degrees. 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 30 degrees of bank and standard rate, or three degrees per second of turn. He continued to search for the traffic until he saw the Cessna directly in front “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 one second. He tried to maintain control of the F-16, but determined that continued controlled flight wasn’t possible, so he ejected.
The air traffic controller said when the F-16 entered the airspace, she descended it to 1,600 feet because that was the minimum vectoring altitude. She stated that this was her usual technique. She said when she noticed the Cessna depart from KMKS, she thought that it would remain in the local traffic pattern. She descended a two-aircraft flight of F-16s to sequence them behind the accident F-16. She asked the two-aircraft flight to expedite its descent to 3,000 feet and noticed that the Cessna was climbing above 1,000 feet.
As the radar targets were continuing to get closer, she told the F-16 pilot that if he did not have the traffic in sight to turn left heading 180 immediately. She said that the 180 degrees 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 conflict alert generated by the ATC radar system. The controller indicated she decided not to climb the F-16 because the Cessna’s altitude on radar was unconfirmed.
Two witnesses who saw the airplanes just before the collision agreed that the Cessna was flying roughly from west to east, and the F-16 was going from north to south. After it hit the left side of the Cessna, debris began falling.
The weather conditions reported at KMKS at 10:55 included calm wind, 10 statute miles visibility and scattered clouds at 2,600 feet. At KCHS, wind was from 220 degrees at seven knots, visibility was 10 statute miles, and there were scattered clouds at 4,000 feet.
According to the Air Force, the F-16 pilot had 2,383 total hours of military flight experience, including 624 hours in the F-16. He was medically qualified for flight duty and was wearing contact lenses at the time of the accident. The F-16 pilot told the NTSB he had accumulated about 50 hours of civilian flying experience and held an FAA commercial certificate.
The Cessna pilot held a private certificate for airplane single-engine land and an FAA third-class medical certificate no waivers or limitations. His logbook showed 244 total flight hours with 239 in Cessna 150s.
The Charleston approach controller served as a controller in the Air Force from 1998 to 2000, and was hired by the FAA in 2006. She was qualified and current on all operating positions at the Charleston FAA facility.
The Cessna had a rotating beacon, anti-collision strobe lights, navigation position lights and a landing light. Investigators couldn’t determine the operational status of each lighting system at the time of the accident. It did not have a traffic advisory or collision avoidance system or ADS-B. The most recent 24-month transponder and encoder tests per FAR requirements shown in aircraft records were from September 8, 2008.
The gray-color F-16 was a single-seat, turbofan-powered fighter airplane. USAF maintenance personnel completed work on the airplane’s flight control system and cleared the airplane to return to service on July 2, 2015. At the time of the accident, the airframe had accumulated 4,435 hours. The airplane was not equipped with traffic advisory, TCAS or ADS-B equipment.
The airplane did have radar installed in the nose. The pilot could use it to locate and “lock onto” other aircraft. The radar could scan 120 degrees directly in front (60 degrees 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. It 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 NTSB determined that the probable cause of this accident was 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.
Note the acknowledgement of see-and-avoid limitations in the probable cause statement. I find it refreshing after so many years of “pilots’ failure to see-and-avoid each other” being a standard feature of midair collision probable causes. If the cure-all for midairs is to be technology as the NTSB suggests, we had better be sure that the technology is reliable and ubiquitous. For example, someone needs to ask: “Can ADS-B really be the answer to eliminating the midair threat if it’s not required to be operating in every aircraft, everywhere?”
Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, visit www.ntsbreporter.us or write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, NY 10602-0831.