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Air Safety Institute Safety Spotlight

Caution: wake turbulence

Most general aviation pilots know they need to maintain a safe distance from larger aircraft during approach and landing. The question that arises is "How much distance?" On July 2, 2003, the pilot of a Beech Baron and one of his passengers were killed during an encounter with wake turbulence while on approach to Runway 36R at Memphis International Airport. Two passengers were seriously injured in the accident.

The pilot of the Baron was communicating with Memphis Approach and was told to expect the ILS to Runway 36R. The pilot was then asked to slow down the Baron to 170 knots and was cautioned about wake turbulence from an ERJ 145 regional jet on approach to Runway 36C approximately four miles ahead. The Baron was vectored and cleared for the ILS Runway 36R approach.

A pilot taxiing between Runways 36R and 36C saw the Baron on final approach and stated that it was about 10 to 15 feet above the runway, and "had it made." The Baron then yawed and rolled to the left, appearing to try a sidestep maneuver to the other runway. The airplane then pitched up about 15 degrees, abruptly snap-rolled to the left, and hit the ground inverted.

The investigation revealed that the Baron was about 3.5 miles behind the ERJ and that the "wake vortex of the ERJ 145, in particular the right wing tip vortex (downwind counterclockwise rotating), could have migrated toward the Baron's flight path. An airplane's typical response to a counterclockwise rotating wake vortex would be to roll to the left."

According to the Air Traffic Controller's Handbook (FAA Order 7110.65R), controllers should consider runways fewer than 2,500 feet apart (such as Runways 36C and 36R) as a single runway for wake turbulence purposes. The handbook also specifies a separation of four miles for small aircraft landing behind a large aircraft.

The NTSB determined the cause of this accident to be an encounter with wake turbulence on approach, which led to the pilot's inability to maintain control and subsequent collision with the ground.

According to the Aeronautical Information Manual, when landing behind a larger aircraft (including on a parallel runway┬┐within 2,500 feet), stay at or above the larger aircraft's final approach flight path, note its touchdown point, and then land beyond it.

To learn more about wake turbulence and how to avoid it, take the Sporty's Safety Quiz on wake turbulence, and read Bruce Landsberg's "Wake Turbulence: Should You Worry?" from the October 1998 issue of AOPA Pilot magazine.

Kristen Hummel manages the GA accident database for the AOPA Air Safety Foundation. She holds a commercial pilot certificate with multiengine and instrument ratings.

By Kristen Hummel

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