As we passed our first waypoint of 20 degrees longitude westbound over the North Atlantic, my copilot and I studied the TCAS symbol on the navigation display. Another airplane was approaching us from behind at the 5 o’clock position. Our 777 was cruising at FL 390. The other airplane was 1,000 feet below at FL 380. Within minutes, the anonymous jet appeared in view from the copilot’s side window.
“Great photo op, Boss,” my copilot announced as he stared outside.
“Who is it?” I inquired.
“Air France. It’s an A380.”
“Just happen to have my camera available,” I remarked.
I unbuckled, rose from my seat and retrieved the Nikon from my laptop bag. Taking a step toward the copilot’s window, I took in the view. Yup, it was definitely a Kodak moment. The A380 was gliding by at a speed of Mach .85, .02 Mach faster than us. I considered pushing the thrust levers up and matching the speed for pure gamesmanship, but burning more fuel didn’t make sense just for entertainment purposes.
As my camera clicked away, I made a subjective observation. The A380 has a majestic quality in flight. On the ground, the airplane has no sex appeal. I’m sorry, but a Beluga whale pregnant with twins is more attractive.
Once my marginal attempts at photography were complete, I retreated back to the left seat with the Nikon. A quick scan of my pictures revealed I’d managed to capture a few decent shots — cool.
Proud of my accomplishment, I keyed the mic on the air-to-air frequency and hailed the Air France flight. When the captain responded, I offered to e-mail the photos. He was appreciative. We exchanged a few more pleasantries and some A380 trivia. Unfortunately, we would have another exchange, but through no deliberate fault of Air France, this encounter wasn’t as pleasant.
It is accepted fact that most international airline war stories begin with, “When the captain was on break …” This short story is no exception.
A few hours later, my bladder and caffeine levels were at polar opposites. I excused myself and exited the cockpit. After my lavatory visit, the next order of business was a cup of java. I trotted into the first-class galley. As I began to pour, the airplane experienced a rapid succession of intense turbulence. We began a pronounced roll to the left. The very pleasant and seasoned flight attendant I had engaged in conversation grabbed the nearest stationary piece of galley equipment for support. Her smile was replaced by a wide-eyed expression.
The seatbelt sign soon illuminated. Within moments, the intercom phone chimed. The flight attendant reached for the handset. My copilot was calling. He was commanding all flight attendants to be seated. Imagine that.
By the sharpness of the bumps and the definitive bank of the airplane, I had a good idea that we had not encountered your garden-variety clear-air turbulence. I stumbled my way to the interphone and called my copilot, indicating an urgent desire to return to the cockpit.
I hopped back into the left seat only to be greeted by another bout of turbulence. Suspecting foul play, I glanced at the traffic symbol on the TCAS display. Sure enough, another airplane cruised directly ahead of us at FL 400. I immediately pushed the heading select button on the eyebrow of the glareshield and turned us 30 degrees to the right.
In spectacular fashion, I watched as a wispy spiraling circle rocketed back toward us. It was a wingtip vortex. Never in my career had I actually seen one in its entirety at cruise altitude. The vortex once again appeared, buffeting the airplane. I instructed my copilot to ask Gander Center for an immediate altitude change to FL 400. I pressed the vertical-speed button on the glareshield eyebrow and rotated the dial to a 500 fpm rate of climb. I wasn’t going to wait for the next encounter. Within moments, another wispy spiral sped its way back toward our position. Only this time, we missed its wrath.
Our clearance request was granted without delay. I continued our climb, selecting the more efficient VNAV mode. Utilizing heading mode, I corrected our slight deviation away from the course line until LNAV re-engaged. Once level, through the observation process of the TCAS and radio chatter, we determined that our friends at Air France had cut my coffee break short. They had climbed above us at some point down the road.
I now have a new regard for the size of an A380. Perhaps the airplane was seeking revenge for my opinion of its appearance. My apologies once again, Airbus. I’m a Boeing guy.
A day later, I attached the photos to the e-mail message I sent the Air France captain. With a humorous tone, I expressed my lack of appreciation for sending us his wingtip vortices. The captain replied with an equally humorous apology. He hoped I hadn’t informed my passengers as to the airline that caused the wild ride. I hadn’t.
Contemplating the wake turbulence encounter, I realized the extraordinary circumstances that led to the event.
First, consider that airplanes utilizing the North Atlantic Track System are separated longitudinally by time. The protocol for the separation is called the Mach number technique. Each airplane entering the NATS is assigned an indicated Mach speed. This speed assignment allows for the required minimum longitudinal separation of 10 minutes. Although this type of separation wasn’t a factor because our airplanes were at different altitudes, we still had to fit into the grand scheme with other flights.
Second, consider the established science known about wingtip vortices. Vortices are created by the high-pressure air curling from under the wingtip toward the low-pressure air on top of the wingtip. A horizontal tornado is formed that rotates clockwise from the left wing and counterclockwise from the right wing. In a static environment, the vortices flow downward approximately 500 to 900 feet and spread out laterally up to five miles. In the first 30 seconds, this downward flow can occur at 300 to 500 fpm.
From private pilots to airline transport pilots, the keywords heavy and slow have been drilled into our brains regarding the worst-case scenario for wake turbulence. We are all aware that takeoff and landing configurations generate the most dangerous opportunities for a vortex encounter. Air traffic control is bound by specific separation requirements for this reason.
But with the theoretical characteristics of wingtip vortices described above, the jet-stream environment does not seem conducive to their survival. High-speed winds, oftentimes in excess of 100 knots, and vertical-shear areas are all part of the high altitude flow. These conditions would seem to break up the phenomenon in short order.
Apparently, we flew into the perfect environmental storm for wingtip vortice survival. When the event occurred, the A380 was an estimated 50 miles ahead and 1,000 feet above. I don’t recall the exact wind, but I believe it was approximately 70 knots from the southwest. Before I left the cockpit, the ride had been occasional light chop, indicating a relatively benign shear situation.
As a very unscientific and marginal attempt at an explanation, it is my belief that the high speed of the jet stream pushed the high speed of the A380 wake even faster. The faster speed provided the vortices with aerodynamic lift, slowing their normal descent rate.
With the jet stream flowing at a slight angle across the track, both vortices shifted horizontally to the right. This explains why the airplane rolled to the left even with the autopilot engaged. The corkscrew spiral I witnessed was spinning clockwise. A clockwise spiral could have originated only from the A380’s left wing. When the vortex collided with the top of the left wing on our 777, it forced a left bank.
Although Air France was a fair distance away, we were traveling at Mach number speeds, which allowed us to reach the disturbed air ahead of us in a short period of time. The turbulence was rapid and intense. The sensation was similar to a sports car rolling over speed bumps spaced apart like highway rumble strips. Despite the alarming surprise, discomfort was the only effect on our passengers and crew. No injuries occurred.
My airline is an advocate of SLOP (strategic lateral offset procedures). The procedure provides for a lateral offset from the assigned course either one or two miles to the right. Because of the extreme accuracy of navigation systems and the possibility that a conflict could occur if an airplane emergency were to require an immediate descent, it is highly recommended. And, of course, the procedure is also beneficial in avoiding wake turbulence. Had I been utilizing SLOP, the vortices encounter may never have occurred.
Regardless, I harbor no ill will toward my Air France brethren. It was an innocent assault — lesson learned.