Chugiak, AK, USA
N4488B
Cessna 170B
N5049A
Cessna 172
Two airplanes, a Cessna 172, and a Cessna 170B, collided in mid air during cruise flight in day visual flight rules meteorological conditions. The 172, piloted by a solo commercial pilot, was traveling in a west-southwest direction. The 170B, with an airline transport certificated pilot and three passengers, was flying northbound, at an estimated altitude between 1,500 and 2,000 feet. A pilot-rated ground witness said he saw the two airplanes collide. He stated that as the Cessna 172 approached the Cessna 170B's right side, and as their flight paths converged, he heard the 172's engine power increase, and then saw the airplane pitch-up sharply. He said the two airplanes then collided, with the 170B striking the left side of the 172. Both airplanes became momentarily entwined, and then fell vertically to the ground. An examination of the wreckage disclosed impact signatures consistent with the witness's statement, with the 170B displaying black tire rubber deposits on portions of the white paint that covered the left lift strut. Traces of black, tire material were also discovered on portions of the 170B's propeller assembly. The Cessna 172's left main tire and inner tube were slashed longitudinally, consistent with a propeller strike, through to the aluminum wheel hub assembly. No radar coverage existed for the air space near the accident site, and neither pilot was in communication with any air traffic control facility. Toxicological samples were submitted from both pilots, and both tested negative for alcohol or drugs.
HISTORY OF FLIGHT On April 23, 2006, about 1158 Alaska daylight time, a wheel-equipped Cessna 170B airplane, N4488B, and a wheel-equipped Cessna 172 airplane, N5049A, collided in midair, approximately 7 miles north-northwest of Chugiak, Alaska. Both airplanes were being operated as visual flight rules (VFR) personal flights under Title 14, CFR Part 91, in visual meteorological conditions when the accident occurred. The certificated airline transport pilot, and the three passengers aboard the Cessna 170B, sustained fatal injuries. The sole occupant of the Cessna 172, a certificated commercial pilot, also sustained fatal injures. Both airplanes were destroyed during the collision, uncontrolled descent, and impact with tidal mud flats. Both airplanes were based at the Birchwood Airport, Chugiak. The Cessna 170B departed from the Birchwood Airport about 1153, and a VFR flight plan was filed for the flight to Talkeetna, Alaska. The Cessna 172 departed from the Birchwood Airport at an unknown time, for a local area flight. During on-scene interviews with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on April 23, witnesses reported that they observed the Cessna 170B traveling north-northwest, between 1,500 and 2,000 feet msl, and a Cessna 172 traveling in a southwesterly direction. About 30 seconds later, the witnesses described hearing a "loud explosion" which directed their attention almost directly overhead. The witnesses reported seeing both airplanes entwined, descending vertically. As their descent continued, they separated, and struck the tidal mud flats in a nose low attitude. The witnesses said that as the Cessna 170B continued its vertical descent the left wing separated, and the airplane rotated counter-clockwise in a descending spiral. During a telephone conversation with the NTSB IIC on April 25, a pilot-rated witness who saw both airplanes just before, during, and after the collision, said that he witnessed the accident from his driveway, located about a half-mile north of the accident site. He said that as he watched the Cessna 170B fly north-northwest, at an estimated altitude of 2,000 feet msl, he observed the Cessna 172 traveling in an west-southwesterly direction, approaching the Cessna 170B's right side. He said that as the airplane's flight tracks converged, and just before impact, he heard the Cessna 172's engine noise increase significantly, followed by a sharp nose-up maneuver. The witness stated that the north-northwest bound Cessna 170B subsequently collided with the west-southwest bound Cessna 172's left side of the fuselage, resulting in the subsequent breakup of both airplanes. According to a family friend, the pilot of the Cessna 170B was en route to a Civil Air Patrol social gathering in Talkeetna, along with three of his children. According to a family member of the Cessna 172 pilot, the accident airplane had just undergone an annual inspection, and the short local area flight was the first flight after the inspection. PERSONNEL INFORMATION Cessna 170B, N4488B: At the time of the accident, the pilot of the Cessna 170B was employed by a commercial air carrier as a Boeing 737 captain. He held a multi-engine land airline transport pilot certificate with type ratings for Boeing 737 and Lockheed L-382 aircraft. He had a flight engineer rating for turboprop engine airplanes, as well as commercial pilot privileges for airplane single-engine land and sea, glider, and rotorcraft. He also held an instrument rotorcraft rating. Additionally, he was a certificated flight instructor, with airplane single and multi-engine, instrument airplane, and glider ratings. His most recent first-class medical certificate was issued on November 4, 2005, and contained no limitations. No personal flight records were located for the pilot, and the aeronautical experience listed on page 3 of this report was obtained from a review of the airman's FAA records on file in the Airman and Medical Records Center in Oklahoma City. On the pilot's last application for medical certificate, dated November 4, 2005, the pilot indicated that his total aeronautical (civilian) experience consisted of about 7,000 hours, of which 200 were accrued in the previous 6 months. Cessna 172, N5049A: At the time of the accident, the pilot of the Cessna 172 was employed as the Alaska Regional Aviation Manager for the U.S. Fish and Wildlife Service. He held a commercial pilot certificate with airplane single-engine land, single-engine sea, and instrument airplane ratings. He also held a flight instructor certificate with an airplane single-engine land rating. His most recent second-class medical certificate was issued on December 13, 2005, and contained the limitation that he possess glasses for near and intermediate vision. No personal flight records were located for the pilot, and the aeronautical experience listed on page 3 of this report was obtained from a review of the airman's FAA records on file in the Airman and Medical Records Center in Oklahoma City. On the pilot's last application for medical certificate, dated December 13, 2005, he indicated that his total aeronautical experience consisted of about 12,200 hours, of which 100 were accrued in the previous 6 months. AIRCRAFT INFORMATION Cessna 170B, N4488B: An examination of the Cessna 170B's airframe logbook revealed the airplane was manufactured on April 19, 1955. The most recent annual inspection was conducted on January 2, 2006. At that time, the airframe logbook listed a total time of 6,812.6 hours. The colors of the airplane included a primary base color of white, with green accent lines. The airplane was equipped with a single, belly mounted, Flight Strobe, Inc., model 4400, high-intensity strobe light unit. Cessna 172, N5049A: An examination of the Cessna 172's airframe logbook revealed the airplane was manufactured on November 10, 1955. The most recent annual inspection was conducted on April 16, 2006. At that time, the airframe logbook listed a total time of 4,299.0 hours. The colors of the airplane included a primary base color of white, with red accent lines. According to photos of the accident airplane taken before the accident, it was equipped with a single, high-intensity strobe light that was mounted on the empennage, atop the vertical stabilizer. METEOROLGICAL INFORMATION The closest official weather observation station is located at the Birchwood Airport, about 7 miles south-southeast of the accident site. At 1156, an Aviation Routine Weather Report (METAR) was reporting in part: Wind, calm; visibility, 10 statute miles; clouds and ceiling, clear; temperature, 41 degrees F; dew point, 31 degrees F; altimeter, 29.89 inHg. COMMUNICATIONS Cessna 170B, N4488B At 1155 the pilot of the Cessna 170B contacted the Palmer Automated Flight Service Station (AFSS), and reported that he had departed from the Birchwood Airport, and then filed a round-robin VFR flight plan, with an anticipated return time of 1600. At 1157, the pilot again contacted the Palmer AFSS specialist on duty and changed the anticipated return time to 1700. No further radio communications were received from the Cessna 170B. The first emergency 911 call was received at the Alaska State Troopers dispatch at 1158. A complete transcript of the recorded radio communications between the pilot and the Palmer AFSS, is included in the public docket of this report. Cessna 172, N5049A There were no recorded radio communications from the pilot of the Cessna 172. The area of the accident did not have any radar coverage. WRECKAGE AND IMPACT INFORMATION The National Transportation Safety Board investigator-in-charge (IIC) examined the wreckage at the accident site on April 23, 2006. The wreckage of the Cessna 170B was located about 478 feet to the north of the Cessna 172. Both aircraft came to rest in an area of tidal mud flats, adjacent to the shoreline of the Knik Arm. Cessna 170B, N4488B The wreckage of the Cessna 170B had extensive ground impact damage. The fuselage of the airplane was in a near vertical, nose down attitude. The longitudinal axis of the fuselage was oriented on a magnetic heading of about 040 degrees. [All heading/bearings noted in this report are oriented toward magnetic north.] Except for the left wing that was severed during the in-flight collision, all of the Cessna 170B's major components were found at the main wreckage area. The Cessna 170B's severed left wing was located about 800 feet southwest of the main wreckage site. The right wing had extensive spanwise leading edge aft crushing, and was oriented with the leading edge down, on about a 45-degree angle. The right wing lift strut remained attached to the wing and lower fuselage attach points. The right wing flight control surfaces remained connected to their respective attach points. The wing carry-through was broken, and crushed in an aft direction. The fuselage was buckled just aft of the rear window. The left wing was severed about 12 inches outboard of the fuselage to wing attach points. The left wing lift strut was severed about halfway between the wing and fuselage attach points. The upper portion of the severed left wing lift strut remained attached to the left wing, and the lower portion of the left wing strut remained attached to the fuselage attach point. A detailed inspection around the fracture area of the left wing lift strut revealed thick, black rubber deposits on the white paint that covered the lift strut. Due to impact damage, the flight controls could not be moved by their respective control mechanisms, but continuity of the flight control cables were established to the cabin/cockpit area. The propeller remained attached to the engine crankshaft. One propeller blade had slight torsional twisting, and significant aft bending about 6 inches outboard from the hub. The second blade had about 20 degree aft bending, about 8 inches outboard from the hub, and slight torsional twisting. Both propeller blades displayed significant "S" bending. Both propeller blade tips were fractured about 5 inches inboard from the blade tip. One of the fractured propeller blade tips was recovered at the accident site. A close-up inspection of the fractured propeller tip revealed a coating of black, rubbery substance, which was consistent with tire rubber. Traces of the black, rubbery material were also discovered on portions of the propeller assembly that remained attached to the engine. The engine cowling, fuselage firewall, and the instrument panel, were crushed and displaced aft. The engine was partially buried in the mud at about a 45-degree angle. It sustained impact damage to the underside and lower front portion of the engine. The forward portion of the crankcase was fractured, which exposed the engine's crankshaft, connecting rods, and pistons. The engine oil sump was crushed upward against the case. The exhaust tubes were crushed and folded, producing sharp creases that were not cracked or broken along the crease. There were no preaccident mechanical anomalies noted with the Cessna 170B airplane. Cessna 172, N5049A The wreckage of the Cessna 172 was located about 478 feet south of the Cessna 170B wreckage. The Cessna 172's severed empennage was located about 600 feet west-northwest of the main wreckage site. The wreckage of the Cessna 172 had extensive ground impact damage. The fuselage of the airplane was in a near vertical, nose down attitude. The longitudinal axis of the fuselage was oriented on a magnetic heading of about 210 degrees. Except for the empennage section that was severed during the in-flight collision, all of the Cessna 172's major components were found at the main wreckage area. Both wings had extensive spanwise leading edge aft crushing, and were oriented with the leading edge down, on about a 45-degree angle. The right wing lift struts remained attached to the wing and lower fuselage attach points. The left wing lift struts remained attached to the wing and fuselage attach points. All of the flight control surfaces remained connected to their respective attach points. Due to impact damage, the flight controls could not be moved by their respective control mechanisms, but continuity of the flight control cables were established to the cabin/cockpit area. The propeller remained attached to the engine. One propeller blade had slight torsional twisting, and significant aft bending about 14 inches inboard from the tip. The second blade had about 70 degree aft bending, about 8 inches outboard from the hub, and slight torsional twisting. The engine cowling, fuselage firewall, and the instrument panel were crushed and displaced aft. The engine was partially buried in the ground at about a 45-degree angle. It sustained impact damage to the underside, and lower front portion of the engine. The left main landing gear leg and wheel assembly was torn from the fuselage, and was discovered in an area of tall grass, located about 150 feet northeast of main wreckage site. The left tire and hub assembly remained attached to the severed spring steel landing leg assembly. The tire and inner tube were slashed, longitudinally, through to the aluminum wheel hub assembly. The aluminum wheel hub assembly had a deep, longitudinal gash adjacent to the inner tube. There were no preaccident mechanical anomalies noted with the Cessna 172 airplane. At the conclusion of the on site wreckage exam, both airplanes were retrieved from the accident site and transported to Wasilla, Alaska. On April 28, 2006, the wreckage of both airplanes were moved to a hangar located in Palmer, Alaska, where the NTSB IIC conducted a wreckage reconstruction exam. Also in attendance was an FAA airworthiness inspector from the Anchorage Flight Standards District Office, and an air safety investigator from Cessna Aircraft. MEDICAL AND PATHOLOGICAL INFORMATION Cessna 170B, N4488B: A postmortem examination of the pilot was conducted under the authority of the Alaska State Medical Examiner, 4500 South Boniface Parkway, Anchorage, Alaska, on April 24, 2006. The examination revealed that the cause of death for the pilot was attributed to blunt force injuries. A toxicological examination was conducted by the FAA's Civil Aeromedical Institute (CAMI) on May 30, 2006, and was negative for any alcohol or drugs. Cessna 172, N5049A: A postmortem examination of the pilot was conducted under the authority of the Alaska State Medical Examiner, 4500 South Boniface Parkway, Anchorage, Alaska, on April 24, 2006. The examination revealed that the cause of death for the pilot was attributed to blunt force injuries. A toxicological examination was conducted by the FAA's Civil Aeromedical Institute (CAMI) on May 30, 2006, and was negative for any alcohol or drugs. WRECKAGE RELEASE The Safety Board released the wreckage of both airplanes to the owner's representatives, at the accident site, on April 23. The Safety Board retained no parts or components.
The inadequate visual lookout by the pilots of both airplanes during cruise flight, which resulted in their failure to see-and-avoid each other, and a subsequent midair collision.
Source: NTSB Aviation Accident Database
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