Jumpseat: Assaulted by an A380
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.