SEATTLE, WA, USA
N39AA
Cessna 150L
While attempting to land long behind a departing Beech D-18, the aircraft encountered wake turbulence that caused it to suddenly roll to the left. Upon encountering the turbulence, the pilot aborted the landing and added full power while attempting to maintain aircraft control. By the time the pilot had reestablished the aircraft in wings-level flight, it had veered to the left and was heading almost 90 degrees from the runway. The pilot then climbed straight ahead, but the aircraft became entangled in electrical transmission lines just after passing the western boundary of the airport. It was later determined that, during the attempted go-around, the pilot had not repositioned the flaps to the 20 degree position called for in the Pilot's Operating Handbook.
On April 9, 1998, approximately 0544 Pacific daylight time, a Cessna 150L, N39AA, became entangled in electrical transmission lines during an aborted landing at Boeing Field/King County International Airport, Seattle, Washington. The commercial pilot, who was the sole occupant, was not injured, and the aircraft, which was owned and operated by the pilot, sustained minor damage. The 14 CFR Part 91 flight, which departed Apex Airpark, Silverdale, Washington, about 20 minutes earlier, was being operated in visual meteorological conditions. No flight plan had been filed, and there was no report of an ELT transmission. According to the pilot, about one minute after he was cleared to land on runway 31 left, he requested an early (close-in) base. After he received approval, he turned base at a point that allowed him to intercept final just beyond the runway threshold. Then, because he was planning to park on a northern portion of the field, he established a rate of descent that he expected would result in a touchdown just north of the control tower (about 6,000 feet down the runway). When the aircraft came abeam the tower, while still about 20 feet in the air, it encountered what the pilot described as "...violent turbulence." He said that the left wing dropped sharply and the aircraft was quickly turned almost 90 degrees to the runway. He then added full power and started climbing straight ahead. Just past the west boundary of the airport, the aircraft became entangled in electrical transmission lines and remained hanging there for about four hours. Eventually, rescue personnel were able to remove the pilot from the aircraft without injury. Once the aircraft was removed from the wires, it was determined that the flaps were still in the full-down position. Upon being questioned, that pilot confirmed that he had failed to reset the flaps to the 20 degree position during the go-around as called for in the Pilot's Operating Handbook. A review of amended tower transcripts revealed that the pilot of the 150 had been cleared to land on runway 31 left about ten seconds after a Beech D-18 (Methow 82) was cleared for departure while waiting at the most southerly hold-short line (A-11) of the same runway. Although the clearance for Methow 82 was given at 0641:10, recorded radar data provided by Seattle Departure showed that it was not until 0643:42, 2 minutes and 32 seconds later, that Methow 82 appeared on radar about 4,000 feet off the departure (north) end of the runway. Recorded radar data also showed that the Cessna 150 turned onto final near the south overrun while about 200 feet above the ground, at 0643:01. This was 41 seconds prior to the D-18 arriving at the aforementioned location. The D-18 was handed off to Seattle Departure at 0643:20, which was about 45 seconds prior to the Cessna 150 experiencing "turbulence." During the investigation it was determined that the Cessna 150 was a Category I aircraft (small aircraft weighing 12,500 pounds or less, with a single propeller driven engine), and the D-18 was a Category II aircraft (small aircraft weighing 12,500 pounds or less, with propeller twin engines). According to FAA Order 7110.65L (Air Traffic Control), proper separation between a Category I aircraft landing behind a departing Category II aircraft ensures that the arriving aircraft does not cross the threshold until the other aircraft has departed and crossed the runway end. But the order further states that if the controller can determine the distance by reference to suitable land marks, and the preceding aircraft is airborne, it need not have crossed the end of the runway if the Category I aircraft is behind the Category II aircraft by at least 3,000 feet. During the investigation, it was also determined that the poles from which the transmission wires hang are not classified as obstructions by the FAA's Flight Standards District Office (FSDO). The basis for that determination was an Aeronautical Study performed by the FSDO, during which the National Oceanographic and Atmospheric Administration's Airport Obstruction Survey Chart was reviewed.
The pilot's failure to reposition the flaps to the 20 degree position during a go-around, as called for in the Pilot's Operating Handbook. Factors include the pilot's decision to land long behind a departing aircraft, an encounter with wake turbulence during the landing sequence, and electric transmission lines in the vicinity of the airport.
Source: NTSB Aviation Accident Database
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