Tip vortex? What is that?

I was a 1,000-plus hour instructor pilot in the T–37 squadron at RND and an experienced platform instructor teaching aerodynamics, instrument procedures, and systems in both the T–37 and T–38 aircraft. On the side I had begun giving flight instruction as a CFI at SAT, flying Cessna 172s and Piper Cherokee 180s.

In the previous three or four months the FAA and the Air Force had issued a flight advisory about clear air turbulence (CAT) following behind and descending from “large aircraft,” whatever that meant. But with close to 1,500 total hours, I believed I could handle anything the weather and other aircraft could throw at me, and I scoffed at tip vortex issues. I was about to find out how serious this phenomenon is.

U.S. Air Force information implied that vortex forces were strong, especially when a small light aircraft might encounter a much larger heavy aircraft at high angles of attack. These vortices follow the jumbo jet and descend some undetermined amount. Word was to stay clear. Like most instructors in the squadron, I read and disregarded this safety advice.

I had begun flying at San Antonio International with John, who happened to be the weather instructor in our squadron, and was scheduled to begin his commercial training in the Cherokee 180. I really don’t recall the first part of this flight which took place almost 25 years ago, but I will never forget the last 10 minutes. We were in the pattern on downwind for Runway 12L when I instructed John to perform a spot landing on the numbers, and he acknowledged. It was not his first spot landing, so I was observing his aircraft control and not deeply involved in instructing. My right elbow was on the armrest, right hand on the top canopy bow; my left arm was behind John to allow more room in the cockpit. My feet were flat on the floor. John had both feet on the rudder pedals, the yoke in his left hand and throttle in his right hand.

It was a fair weather day with quartering winds less than 10 knots from the right, and we were about to turn left base when we heard tower clear an American Airlines DC–8 (the original jumbo jet) for takeoff on 12R. These two parallel runways are fairly close, and the threshold for 12L is displaced about 1,500 feet. That meant that as we turned the Cherokee to base we were looking straight at the DC–8 as the aircraft on the surface added power and turned from the taxiway to 12R with jet blast barreling from four engines.

John was concentrating on his pattern and spot landing as I watched the American Airlines flight accelerate in front of us, to the right. As we descended, the DC–8 accelerated away from us, lifted the nose, and got airborne. We made our spot landing and John added power to accelerate. It took a few seconds to accelerate to flying speed and John made a good takeoff.

Immediately following liftoff, at maybe 10 feet of altitude with about 70 knots—nose high and accelerating—the Cherokee began an abrupt and strong roll to the left. Without making a control input, John looked at me and yelled, “What are you doing?”

If we were to live through this situation, I had to take control, but I was spread out, feet still flat on the floor. The left roll rate was increasing and we weren’t even 20 feet airborne. My right hand came down hard on the yoke to bank right—opposite the roll rate—as my left hand came over John to the top of the yoke. The yoke hit the right roll stop as my left hand grabbed the yoke. Because the roll had not stopped, I thought I must have rolled the wrong way, and for a micro-instant, with two hands on the yoke, I started to roll back to the left, just as the left bank angle went past 90 degrees. The Cherokee was still barely airborne, and I was looking at John and over him directly at the ground only 25 feet away. With my aerobatic proficiency I recognized what was happening and knew how serious it was.

We were seriously in a DC–8 tip vortex.

Simultaneously with the hand movement, I lifted my feet to the rudders. As I moved the yoke hard to the right (anti-roll) the second time, I started depression of the right rudder. At just that instant the right wing came out of the vortex and the airplane came to level but climbing flight at 75 knots, not yet at 75 feet altitude. Our heading had shifted from 120 to 80 degrees, approximately.

Climbing crosswind to pattern altitude, I called SAT tower asking if they observed what had happened from the DC–8. They responded that they thought we were turning to avoid the vortex; I responded that we were in the vortex! We proceeded to pattern altitude, shaken, and entered downwind for a normal full-stop landing. I had several takeaways from this flight:

1. Macho military flying, while giving you confidence, will not save you unless you take immediate action.
2. Wake turbulence will kill you. Pay attention.
3. Never fly as a CFI with feet flat on the floor.
4. Take control of the aircraft for flight safety and to save lives.
5. In a sudden flight emergency, take action first and talk later.

Jim Gardner is a pilot with more than 6,600 flight hours, and he is the owner of a Piper Twin Comanche.