Wake turbulence, collision avoidance and runway safety
9 min readLesson 37 of 59
- Explain how wake turbulence forms and moves
- Avoid wake turbulence on takeoff and landing
- Use a good scan and know the rules for LAHSO
Wake turbulence
Every airplane that makes lift makes wingtip vortices. They're strongest behind airplanes that are heavy, clean (gear and flaps up) and slow, like a large jet on takeoff or approach. A light airplane flying into one can be rolled faster than its ailerons can counter.
Vortices sink (generally a few hundred feet per minute) and level off below the generating airplane's flight path. Near the ground, they drift outward and can be held over the runway by a light crosswind. A light quartering tailwind is the worst case, because it can push a vortex back into the touchdown zone.
How to avoid it
- Landing behind a larger airplane: stay at or above its flight path and land beyond its touchdown point.
- Taking off behind a larger airplane: lift off before its rotation point and climb above its path, or wait.
- Helicopters make strong vortices too, especially when hover-taxiing.
Collision avoidance
Most midair collisions happen in good weather, near airports. The best scan moves your eyes in small steps, about 10° at a time, focusing about a second on each, because your eyes can't spot motion while they're sweeping. Another airplane on a collision course appears to have no relative motion; it just gets bigger, suddenly.
Runway safety
- Know where you are on the airport: use the airport diagram, and ask for help ("progressive taxi") if lost.
- LAHSO (land and hold short operations) asks you to stop before an intersecting runway. Student pilots should not participate, and any pilot in command can decline.
- Never cross a runway hold short line without a clearance at a towered airport.
Key takeaways
- Wake turbulence is worst behind heavy, clean, slow airplanes.
- Land beyond their touchdown point; take off before their rotation point.
- Scan in 10° steps; a collision threat shows no relative motion.
What the examiner may ask
Practice answering out loud before you open each answer.
How do you avoid wake turbulence landing behind a larger airplane?
What wind is most dangerous for wake turbulence on the runway?
Describe an effective scan.
Common mistakes
- Departing right behind a heavy airplane without waiting.
- Fixating inside the cockpit during busy phases.
- Accepting LAHSO without knowing the available landing distance.
Read it in the FAA sources
Lesson check
Get every question right to complete the lesson. Take your time; wrong answers explain why.
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