CEN13FA438

An encounter with wake turbulence, which resulted in the pilot’s loss of control of the airplane and its subsequent in-flight breakup. Contributing to the accident was the approach controller’s failure to issue a wake turbulence advisory to the pilot.

The pilot was receiving flight-following services from an approach controller, who gave the pilot vectors to fly east over Lake Michigan and then north to avoid conflicting traffic. On the northerly heading, the accident pilot flew 1.4 miles behind the other airplane. When the accident pilot had the traffic in sight, the approach controller allowed him to pass behind the other airplane and then turn northbound as requested. Shortly thereafter, the approach controller lost radar contact with the pilot. Search and rescue operations were conducted, and the airplane was located in the lake. According to recorded radar data, the accident airplane's flightpath crossed the other airplane's flightpath at 1,800 feet mean sea level (msl) about 39 seconds after the other airplane passed the same location at the same altitude. Because the approach controller's plan explicitly had the accident pilot pass behind the other airplane and the other airplane was descending from above the accident airplane, it is likely that the accident airplane encountered wake turbulence. Primary radar returns detected by airport surveillance radar were consistent with the in-flight breakup of the airplane. The approach controller did not issue a wake turbulence advisory to the pilot. Although wake turbulence is primarily the pilot's responsibility, the Federal Aviation Administration Air Traffic Control Handbook does require controllers to provide pilots with a wake turbulence advisory if, in the controller's opinion, wake turbulence may adversely affect their aircraft. In this case, the approach controller should have been cognizant of the potential hazard and issued a wake turbulence advisory to the pilot.

Air Traffic Control Information The accident airplane was radar identified at 1431:37, 1 mile north of the Racine airport climbing under VFR to 1,500 feet. At 1435:42, the MKE controller transmitted, "November four nine x-ray if you could turn to the east I do have traffic (inbound) for runway two five left I'll point them out and then you can pass behind them." The pilot responded, "all right." The controller then issued a traffic advisory about N1549X to Delta Airlines flight 931 (DAL931) and transferred the Delta flight to the tower frequency. At 1436:25, the controller instructed the pilot of N1549X to turn right heading 090 and the pilot acknowledged. The controller continued, "…there is traffic just to you ah twelve o'clock and about two miles descending out of two thousand three hundred, an MD-80." The pilot replied, "all right, I can go down lower if you like" The controller responded, "…negative I need you just to turn out of there then I'll get you northbound as soon as I can." The pilot then stated, "OK, I've got them in sight." The controller replied, "…thank you, just pass behind that traffic and then you can proceed northbound as requested." The pilot responded, "All right." At 1437:34, the MKE approach controller advised the local controller in the tower that the pilot of N1549X had the Delta flight in sight. At 1438:11, the approach controller attempted to advise the pilot that radar contact was lost, with no response. There was no further contact with the pilot. According to recorded radar data, the flight path of N1549X crossed the flight path of DAL931at 1437:51 at 1,800 feet, which was 39 seconds after DAL931 passed the same point at the same altitude. At the time of the accident, N1549X was operating within Milwaukee Class C airspace and was subject to mandatory separation. Separation, traffic advisories, and safety alerts are to be issued between IFR and VFR aircraft. In addition to the standard separation requirements above, controllers are also required to issue wake turbulence advisories when, in their opinion, wake may have an adverse effect on an aircraft. Since wake turbulence is unpredictable, the controller is not responsible for anticipating its existence or effect. An FAA Advisory Circular states that vortex visualization and avoidance procedures should be exercised by pilots using the same degree of concern as in collision avoidance. Pilots are reminded that in operations conducted behind all aircraft, acceptance of instructions from ATC in the following situations is an acknowledgment that the pilot will ensure safe takeoff and landing intervals, and accepts the responsibility for providing wake turbulence separation: traffic information; instructions to follow an aircraft; the acceptance of a visual approach clearance. Under certain conditions, ATC applies procedures for separating IFR aircraft. If a pilot accepts a clearance to visually follow a preceding aircraft, the pilot accepts responsibility for separation and wake turbulence avoidance. The controllers will also provide to VFR aircraft, with whom they are in communication and which in the tower's opinion may be adversely affected by wake turbulence from a larger aircraft, the position, altitude and direction of flight of larger aircraft followed by the phrase "CAUTION - WAKE TURBULENCE." After issuing the caution for wake turbulence, the controllers generally do not provide additional information to the following aircraft unless they know the following aircraft is overtaking the preceding aircraft. Whether or not a warning or information has been given, however, the pilot is expected to adjust aircraft operations and flight path as necessary to preclude serious wake turbulence encounters. Radar Data The radar data used for this investigation was obtained from the ASR-9 airport surveillance radar located at MKE. N1549X was observed from immediately after departure at Racine until the end of the flight southeast of MKE. Just before the accident, the airplane presented a normal transponder return showing 1,500 to 1,600 feet altitude. At 1437:45, the altitude readout dropped to 0, which was likely representing unintelligible/unusable altitude data, and then showed 1,800 feet by 1437:49. The last MKE transponder return occurred at 1437:54, reporting the airplane's altitude as 1,400 feet. Beginning at 1437:54, four primary (non-transponder) radar returns were detected by the radar, originating just before the target where N1549X reported an altitude of 1,800 feet. An autopsy was performed on the pilot on July 29, 2013, by the Milwaukee County Medical Examiner's Office, Milwaukee, Wisconsin. The cause of death was determined to be multiple blunt force injuries and the manner of death was an accident. The FAA Civil Aerospace Medical Institute (CAMI) prepared a Final Forensic Toxicology Fatal Accident Report. The results were negative for all screened substances. An autopsy was performed on the second pilot on July 29, 2013, by the Milwaukee County Medical Examiner's Office, Milwaukee, Wisconsin. The cause of death was determined to be multiple blunt force injuries and the manner of death was an accident. The FAA CAMI prepared a Final Forensic Toxicology Fatal Accident Report. The results were negative for all screened substances. At 1452, an automated weather reporting facility at KMKE, located 3 nautical miles west of the accident site, reported wind from 300 degrees at 13 knots, 10 miles visibility, scattered clouds at 3,400 feet, an overcast cloud layer at 4,000 feet, temperature 61 degrees Fahrenheit (F), dewpoint 45 degrees F, and a barometric pressure of 29.91 inches of mercury. The main wreckage was located in Lake Michigan at 42:57.883 N, 087:49.06 W, at a depth of 46 feet. The site was 3.2 miles east of the departure end of runway 25L at KMKE and 1.2 miles from the shoreline of Cudahy, Wisconsin. The airplane was fragmented and pieces were scattered along the bottom of the lake. About 50% of the airplane was recovered during the extraction process. The fuselage was noted to be broken into three sections. The left wing separated from the fuselage. The outboard section, including the aileron, was not recovered. The right wing inboard section remained attached to the fuselage. The rudder was attached to the vertical stabilizer at its hinge points and was impact damaged. The stabilator was attached to its mounting blocks. The flight control cables were continuous from the cockpit controls to the rudder and stabilator. The flight control cables remained attached at both aileron bell cranks. Both aileron control cables were separated in overload near the wing roots. The landing gear was in the retracted position. The main landing gear were found in the wheel wells. The nose landing gear separated from the fuselage. The engine control lever console separated from the instrument panel, the levers were in a forward position, and the friction lock was on. The engine control cables for the throttle, propeller, and mixture controls were attached to their respective levers. The engine was rotated by turning the propeller; continuity of the crankshaft to the rear gears and to the valve train was confirmed. Compression and suction was observed from all four cylinders. The interiors of the cylinders were examined using a lighted borescope. The only anomalies noted were water and mud in the cylinders. Both magnetos were operated by hand and neither would produce a spark. They were disassembled and no damage was noted to the internal components other than water contamination. The spark plugs were all intact and observed as light brown, revealed signs of normal operation, and some were covered in mud. Water residue and a small amount of oil were observed in the engine crankcase. The oil cooler was separated from the engine baffling and was impact damaged. The propeller blades remained secured in the propeller hub and atta