The NTSB and Air Force are investigating a 7 July midair between an F-16CM Viper and a Cessna 150. Two aboard the Cessna died, the fighter pilot was uninjured, both planes were destroyed.
It seems clear that the father and son in the Cessna 150 didn’t suffer. The F-16CM was traveling at over 200 kts over South Carolina 7 July, when it flew through the center of the 1670 pound light plane (and its two occupants). The damaged jet continued briefly, but three minutes after the collision, the pilot ejected. Most of the jet landed in a single crater, where it exploded and burned itself out. The little Cessna and its pilots came fluttering down in pieces; some of the larger ones, like the plane’s 100-horsepower engine, never were found. The jet pilot was, thanks to dumb luck, completely uninjured, neither by the midair nor by the ejection. Any other roll of the die and this would have been a mishap with three fatalities.
As is usually the case with midair collisions, it was 11 AM on a clear day (there were scattered clouds, but they were over 1000 feet higher than the collision) with excellent visibility. As is often the case, both aircraft were clearly on radar. However, only one of them was flying under positive air traffic control, under instrument flight rules. That was the Air Force jet.
Both aircraft were on the screen and known to the controller at the time of impact, as the F-16 pilot practiced instrument approaches (these are flights down electronic beams or pathways that are used for landing in bad weather. Because they’re a perishable skill, pilots practice them routinely in good weather, as this man was doing). He was very busy; he was vectoring to start his third approach in a flight that began only 40 minutes prior, this time a TACAN approach — a military electronic beam of 1950s vintage, conceptually similar but technically different and more precise than the VORs used by civilians. Instrument flying, and especially setting up instrument approaches, demands that the pilot be head down in the cockpit to some degree (you can fight the F-16 through the HUD, but you can’t set up an approach that way. You have to set a bunch of knobs and dials inside the jet). When civilians and most multi-crew military pilots fly practice approaches, they usually have the second pilot looking out of the cockpit as a safety pilot. In a single-seat fighter, that’s not an option. The pilot began to look for the Cessna when the controller called it out to him. He didn’t see it.
The controller made several calls to the F-16 as it became clear that the jet was on a collision course with the light plane. The pilot didn’t seem to react at first, and then, when told to turn immediately, he slowly began a wide sweeping turn that was too little, too late. The Cessna was not talking to approach control (and wasn’t required to); it did have a radar transponder squawking the Mode III code (1200) for an aircraft flying under visual flight rules.
Here’s a hasty transcript of the radio traffic, reconstructed from the NTSB preliminary. CHS is the Charleston approach controller; N3601V or 01V is the Cessna, not that it appears; we’ll use F16 for the jet’s callsign. The jet was heading about 215 degrees at about 200 knots, and the Cessna about 110 degrees at about 90 knots, so they were closing rapidly.
1100:18: CHS->F16, Traffic 12 o’clock, 2 miles, opposite direction, 1,200 indicated, type unknown.
1100:18: F16->CHS, Roger, looking for traffic.
1100:26: CHS->F16, Turn left heading 180 if you don’t have that traffic in sight.
1100:26: F16->CHS, Confirm two miles?
1100:32: CHS->F16, If you don’t have that traffic in sight turn left heading 180 immediately.
1100:49 (last radar return received from Cessna)
1100:52: CHS->F16, Traffic passing below you 1,400 feet.
1101:19: F16 (transmitting blind), Mayday!
1103:17 (last radar return from F-16, indicating 300 feet, near crash site).
The NTSB preliminary does contradict itself. It says, after the 1100:32 call demanding a turn from the F-16:
Over the next 18 seconds, the track of the F-16 began turning southerly.
However, it also indicates that:
At 1100:49, the radar target of the F-16 was located 1/2 nautical mile northeast of the Cessna, at an indicated altitude of 1,500 feet, and was on an approximate track of 215 degrees.
As we noted above, 215 degrees was the jet’s heading before the commanded turn; yet it was still tracking 215 on impact, it says here. However, after the collision the F16 was observed (on radar) to track “generally southerly”.
One thing that’s very clear from this is how quickly this situation developed and went thoroughly pear-shaped. When the controller says “immediate” or “immediately,” that’s a word that gets every pilot’s attention; they only use it when time matters. And from the first traffic call to the “immediately” call was about 14 seconds. Another 17 or so seconds after that, all opportunity to avoid the crash had been lost, two men were dead and one was about to take to the silk. A little more than a half minute elapsed from the controller’s first expression of concern to the collision. A little over three minutes had passed since the Cessna lifted off its runway and was immediately picked up by the ATC radar.
NTSB will have a final transcript with the final report, months from now.
The next couple of paragraphs are speculation about a possible contributing factor in this mishap. Speculation based on early reports, while it is the bread and butter of CNN, is often unwise in aviation mishaps, because early reporting is almost always as wrong as reporters can get. But nonetheless, we’ll go ahead and speculate. Therefore, to control the depth of speculation, the only source that we have used is the preliminary report from NTSB. –Ed.
When the radar images merged and the radar image of the shredded Cessna disappeared, the planes were reporting different altitudes. The transponder of the fighter said it was at 1500 feet (albeit descending); the transponder of the Cessna showed it at 1400 feet (and climbing), seconds before the collision. Because air pressure varies from time to time and place to place, a pilot uses a knob and a dial called a Kollsman window (after its 1930s inventor) to adjust the barometric pressure. A standard day’s pressure is considered to be 29.92 inches of mercury at sea level; locally, there was high pressure (that good sunny weather!) and the setting then and there should have been 31.15.
If the pilot of the jet mistakenly set his altimeter to 31.05, his altimeter would have read 1500 feet when he was actually at 1400 (or, if the pilot of the Cessna had set his to 31.25, he’d have been 100 feet higher than his reported altitude). We’re not sure that the F-16 transponder uses the pilot’s Kollsman setting like the civilian one does. We are fairly confident that if the two planes were correctly reporting that they were both at the same altitude, the controllers would have had much more of a sense of urgency (and automatic features of the system would have flagged their attention) much earlier.
What the Investigation Can and Will Determine
The investigators may be able to tell how the altimeters were set in both planes. On the Cessna, it’s a physical knob and dial, and should preserve its last setting if it was not physically destroyed in the impact. That may have happened. Here’s what the investigators found of the wreckage:
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 approximately 1,200 feet. 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 feet 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 feet southwest. Small pieces of the F-16’s airframe were also distributed throughout the accident site.
Just to give you an idea how thoroughly even the F-16 was parted out inflight, here is the “engine augmenter” referenced above:
Yeah, it landed on a trailer/RV park.
On the Viper, the altimeter setting should be retained in the data recorders, which were recovered in good order from the pilot’s ejection seat and the wreckage of the airplane.
The investigators were last seen dragging the river for missing parts of aircraft and people.
The investigators are likely to recommend that the Board note, among any other findings, that there are inherent limitations to the “see and avoid” principle, but, ultimately, the crew of the two aircraft failed to see and avoid one another.