Wake Turbulence and Spacing Behind a Heavy on a Parallel Approach
You are on a visual approach to a runway, cleared to land, at 140 kt groundspeed, 3 NM final. A heavy four-engine jet has just landed on the parallel runway, whose centreline is 700 m from yours. Wind is a light quartering tailwind for you, roughly 5 kt, blowing from the heavy's runway toward yours. Tower advises the heavy is vacating and clears you to continue. You feel a brief roll and sink at 2 NM final.
1. Explain the wake turbulence mechanism and why this situation is hazardous.
Read the worked answer
A heavy generates counter-rotating wingtip vortices that sink and drift with the wind. With a light wind from the heavy's runway toward yours, the vortices drift across your approach path. A light quartering tailwind also reduces your own control response and increases groundspeed. Encountering a vortex produces an abrupt roll and sink; at low altitude and low speed there is little height to recover. Parallel runways 700 m apart with a crosswind component toward your centreline is a classic wake encounter scenario.
2. What actions do you take after the roll and sink at 2 NM final?
Read the worked answer
Apply prompt but smooth counter-control, add power to arrest the sink, and do not chase the roll with abrupt aileron. If the encounter is significant, go around: apply full power, establish a positive climb, and fly clear of the vortex path. Advise the tower of the wake encounter. If you continue, aim to stay above the heavy's flight path and land beyond its touchdown point, since vortices sink below the generating aircraft's path. Given the low altitude and the near-parallel geometry, the conservative choice is a go-around and re-approach with better spacing.
3. What spacing and technique would you use on the next approach?
Read the worked answer
Request a delay or a wider downwind to increase spacing behind the heavy, or ask for a different runway. On final, stay at or above the heavy's glideslope and touch down beyond its touchdown point to remain above the descending vortices. Maintain a steeper-than-normal approach only if the airplane and conditions allow, and keep speed up slightly for control authority. Avoid the region below and behind the heavy's flight path, and be ready for a go-around if another encounter occurs.