Why did the Viper Centerpunch the Cessna?

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.

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.

Speculation Follows

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:

midair engine augmenter

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.

15 thoughts on “Why did the Viper Centerpunch the Cessna?

  1. Tim, '80s Mech Guy

    Heard about that when it happened, nothing since of course, dead lions and such. From your description the jet jocky would be looking down and just right of center. The private pilot who was climbing ought to have been looking forward and probably would have had trouble spotting a camouflaged target even at relatively low speed, coming down from ten o’clock. A lot of stuff had to line up for this to happen. Seems like that controller will work a little faster to deconflict in future. I assume the pop up who you have no comms with would get the right of way?

  2. Bruce

    Seems like an Air Force pilot that didn’t know what immediately means from a controller if the collision happened 17 seconds later.

  3. Nathan Johnson

    One flaw in that line of reasoning, Mode C transponders report altitude based on standard day(29.92), not the local setting. A 100+ foot difference in altitude suggests a malfunction on one of the aircraft. See the Wikipedia article “Pressure Altitude”, the first reference I could find.

  4. "Greg"

    Whelp… since I don’t think CNN will be commenting here anytime soon, instead I am go ing to jump right in on that! First, copied & pasted the radio traffic…
    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.

    So… at 1100:18, F16 “rogers” presence of traffic, 8 seconds later at 1100:26 CHS instructs F16 to turn left if no visual. 6 more seconds, CHS repeats instruction, adding “immediate”. Then 17 more seconds until “last radar return” at 1100:49… this commenter concludes that F16 pilot is at fault for not following CHS instructions TWICE not to mention where the preliminary report says: “F-16 wreckage path was about 700 feet long and oriented roughly 215 degrees” which suggests that the pilot NEVER turned.
    For the F16 pilot, it might have been better to have died… especially if he loves flying… even if he is cleared by USAF to fly again, he will always be known as the “Cessna killer”

    1. Tim, '80s Mech Guy

      Whack some civilians NOT engaged in a Kamikaze run on the capital and you are probably screwed even if you are in the right, here we are SPECULATING about what APPEARS to be poor judgment, inattention, or failure to rapidly transition from the concentration on setting up the approach… Further speculation, 14-1500 feet doing an approach at 200, one of multiple, not an expert but I’m wondering if he was flaps and gear down? Gear down would mean those bright-assed lights would be on. Jet Boy is looking or trying to look through his right hand for the 150 and the 150 pilot, even if he knew to look was probably looking at the wing root. EPIC BAD LUCK blindspot on blindspot.

  5. Ken

    I’ve done a good bit of fishing off the beach of Tyndall AFB. Fighters overhead all day, close enough to see the pilot. Amazing how they blink out of sight with a little altitude in a hazy sky.

    I can imagine the poor souls in the Cessna being like a possum crossing the road.

  6. Greg

    Yet again BSLA (big sky little airplane) fails. The closest I’ve ever come to dying in my flying career has been several near collisions. One guy went by so close I could clearly see the sectional he was holding up. Head down and locked he was.

  7. gebrauchshund

    One thing that stands out to me is the first transmission of “traffic 12 ‘o clock, 2 miles, opposite direction”, when apparently the two aircraft were closing at nearly right angles. I would imagine the F-16 pilot’s attention was focused directly ahead, and once he banked into the left turn he would have been completely blind to the Cessna approaching from below and to the right. Based on the described damage to the Cessna and the fact that the F-16 continued flying ( albeit briefly ) with no injury to the pilot, I would speculate that it was actually the Cessna that centerpunched the F-16 on the underside of the fuselage toward the rear, tearing loose the engine augmenter in the process. I wouldn’t read too much into the F-16 wreckage being oriented at 215 degrees, or even that it was located 6nm “south” of the Cessna. Given the evidence of damage to the rear of the F-16’s engine it’s reasonably certain that the control surfaces were also severely compromised, so keeping it pointed in any particular direction may have been impossible. Certainly once the pilot punched out the aircraft would go in whatever direction was dictated by the laws of aerodynamics, acting on a severely, and likely asymmetrically, damaged airframe.

  8. Kirk

    I think the bigger question is about air traffic management. Under what regime does it make sense to have a civilian aircraft cleared to climb through airspace allocated to a military jet practicing landing? Even if they’d missed, the wake from that F-16 would have tumbled that little Cessna like a cat in a dryer, and I seriously doubt that they would have survived that, either.

    I know just enough to be dangerous about this stuff, and I’m still looking at this report like that dog looking at the Victrola–It just doesn’t make sense. That pair of aircraft should have been separated by a hell of a lot more than what they were. How’d the Cessna get clearance for takeoff?

    1. Hognose Post author

      Working your ?s back to front.
      At most of the airports in the USA there are no towers and no clearances. You just go.
      I don’t know any pilot who thinks 100′ vertical separation is OK for aircraft not on the same mission.
      Airspace doesn’t get “allocated” except for instrument flight rules (IFR) traffic. There are rules — scads of ’em! — about procedures and required separation. With some exceptions, airplanes can fly almost anywhere under visual flight rules. There are tightly-controlled areas around major jetports (so-called Class B airspace) and some airspace you must be IFR to use (notably Class A airspace, everything from 18,001′ to 60,000 feet MSL). Within 30 NM of a Class B, all aircraft must use an altitude encoding (Mode C) transponder.

      Unless — you’re going to love this exception — they have no electrical system. So if you have an old Cub with no alternator, battery or starter (to start it you swing the prop like the Red Baron did), you’re exempt.

      Mode S transponders and ADS-B enable in-cockpit traffic displays and warnings, but due to FAA regulatory complexities they’re extremely expensive and have not been widely adopted.

      So the civilian a/c was not “cleared to climb” but he was not prohibited from climbing. And he was displaying a secondary radar return, proving that his Mode C transponder was on.

      1. Chris

        It’s been a while since I’ve been flying, but IIRC, an IFR pilot flying in VFR conditions is on his own to maintain separation from VFR traffic. Not to say the F-16 pilot wasn’t extremely busy setting up the approach – but he should have kept his head out of the cockpit enough of the time to be aware of VFR traffic.

  9. Buck

    Read the factual report just yesterday and thought WTH was the F-16 pilot doing and how much airspace was he covering during those important seconds?

    If he’d been driving I’d suspect texting.

    Sad for the departed.

    1. Hognose Post author

      If he’d been driving I’d suspect texting.
      Never done it in an F-16, but setting up an instrument approach (or any significant nav actions) on any of the glass panels I’ve used is a bit fiddly… like texting with a smartphone.

      Fun fact about ATC: it exists to separate IFR traffic from IFR traffic. It doesn’t guarantee you squat on visual traffic, although VFR a/c can participate voluntarily in flight following on a services-available basis. When ATC gets too busy (i.e. the airspace is crowded), they stop calling traffic for VFR users. They will call the VFR traffic for the IFR users (as they did here) but since they’re not always listening or talking to that guy, they don’t know his intentions.

  10. Red

    I know next to nothing about airplanes, so if this question is incredibly stupid go ahead and say so. Wouldn’t the F16 have some sort of radar or warming within the cockpit that would alert him of collision/objects right in his path?

  11. Mac

    Alternative wild-ass speculation: one of the first things a pilot gets when contacting ATC at an airfield is a readback of his call numbers and the current altimeter reading at the field. If anyone had the wrong altimeter setting my money would be on the Cessna. As to 100 ft separation, well nobody is looking to that as anywhere reasonable. A fast mover would probably think passing 100 ft over a Cessna would in and of itself be very bad for the little guy in terms of buffeting alone. I recall a fast mover in Germany years ago that bounced a low flying HH-53. Granted the guy wasn t doing 200 knots but the dirty air collapsed the rotor system
    The guy is dead as is his son so I hesitate to write this but there has been any number of times i have heard the proverbial dentist in a Cessna absolutely clueless as to his location relative to an airport. He had the responsibility to see and avoid.
    Damn I hate defending fighter jocks.

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