San Juan, PR, USA
N73115
CESSNA 172M
About 4 minutes before the accident, the pilot advised an air traffic controller that an aileron cable had broken but that he was continuing to the airport to land. Security video and eyewitness reports revealed that the airplane was at low altitude and appeared to be maintaining level flight until it banked right, descended, and impacted water near the airport in a right-wing-down attitude. A postaccident examination of the wreckage indicated that all of the airplane's flight control cables were lubricated except for a fractured section of aileron control direct cable near the doorpost pulley, which was likely not properly lubricated. Most of the cable strands and the doorpost pulley and bearing exhibited severe corrosion near the fracture. When manipulated by hand, the pulley bearing would not rotate due to the corrosion. Analysis of the cable, doorpost pulley, and an exemplar cable from a similar make and model aircraft that had been flown in similar atmospheric conditions (in what is considered a severe corrosion zone) revealed moderate to severe corrosion. It is likely that, during the airplane's maintenance inspection 6 months before the accident, the mechanic failed to detect the corroded cable due to the difficulty in visually seeing the cable. It is also likely that the doorpost pulley's failure to rotate resulted in tension on the right aileron control cable, which subsequently caused it to fail due to the severe corrosion. The aircraft manufacturer's maintenance manual for the airplane gives specific instructions for lubricating and inspecting flight control cables and pulleys every 600 hours or 12 months, whichever comes first, including, in part, examining the cables for corrosion and the pulleys to ensure smooth rotation. After the accident, the manufacturer produced a video emphasizing the importance of properly examining and lubricating the cables.
HISTORY OF FLIGHT On July 25, 2012, about 1420 Atlantic time zone (AST), a Cessna 172M, N73115, was substantially damaged when it impacted the water near Fernando Luis Ribas Dominicci Airport (TJIG), San Juan, Puerto Rico. Visual meteorological conditions prevailed and a visual flight rules flight plan had been filed. The private pilot was fatally injured. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. The flight originated from Antonio/Nery/Juarbe Pol Airport (TJAB), Arecibo, Puerto Rico. According to numerous eyewitness reports, the airplane appeared to be maintaining level flight and subsequently banked to the right, as viewed from behind, descended, and then impacted the water in a right-wing-down attitude. One eyewitness, located in an aircraft that was following the accident airplane on final approach, reported that the airplane "made some zigzagging" prior to it banking to the right. The airplane was observed impacting the water's surface with the right wing tip. The airplane then cartwheeled and disappeared below the water's surface. According to video taken of a security video monitor, from a camera mounted on a terminal building on the southwest side of the bay, the airplane banked to the right and remained in a continuous bank. The airplane turned about 180 degrees of heading change, facing the direction of travel prior to impacting the water. The airplane was observed impacting the water in a right-wing-low attitude and, within about 2 seconds, disappeared below the water's surface. PERSONNEL INFORMATION According to Federal Aviation Administration (FAA) records, the pilot held a private pilot certificate with an airplane, single engine land rating. The most recent logbook entry that was located, dated September 30, 2011, indicated he had 1,150.9 total hours of flight time. According to information provided on his most recent third class medical certificate application, issued March 3, 2012, he reported 1,175 total hours of flight time. The medical certificate was issued with a limitation for the requirement to wear corrective lenses, and not valid for any class after. AIRCRAFT INFORMATION According to FAA records, the airplane was issued an airworthiness certificate on May 14, 1976 and was registered to the pilot on December 2, 2002. It was equipped with a Lycoming O-320-E2D engine, serial number L-45584-27A. A review of copies of maintenance logbook records showed an annual inspection was completed April 13, 2012, at a recorded tachometer reading of 2,999 hours, and engine time since overhaul of 2,928.0 hours. The tachometer and Hobbs meter were observed at the accident site and indicated 3,009.6 hours and 586.0 flight hours, respectively. The most recent entry that specifically stated when any control cables were lubricated was recorded on January 22, 2010, at a tachometer reading of 2,913.2 hours, and that wan an engine logbook entry. According to an airframe and powerplant (A&P) mechanic, he performed most of the maintenance and on the day of the accident he serviced the nosewheel strut, which was "low." He also performed the last annual inspection; however, he was unsure of the date. According to the inspection authorization (IA) mechanic who signed off on the annual inspection, it was completed about six months prior to the accident. METEOROLOGICAL INFORMATION The 1422 recorded weather observation at TJIG included wind from 110 degrees at 8 knots, visibility 10 miles or greater, scattered clouds at 4,000 feet above ground level (agl), temperature 32 degrees C, dew point 24 degrees C and barometric altimeter setting 30.03 inches of mercury. COMMUNICATION At 1413:00, the pilot made his initial contact with the TJIG Federal Contract Air Traffic Control Tower controller and was subsequently told to make a straight in approach to runway nine and report at the Levittown water tank. At 1416:28, the pilot reported abeam the Levittown water tank. At 1418:13, the pilot stated, "november one one five tower." At 1418:15, the local controller replied, "november one one five tower." At 1418:17, the pilot replied, "i think i got my aileron cable broken ah i am unable to maintain level flight so i'll continue the descent and land." At 1418:27, the tower controller replied, "november one one five you're cleared to land runway niner wind one one zero at six do you require any assistance." At 1418:33, the pilot stated, "i don't know i guess not." No further recorded transmissions were received from the accident airplane. At 1422:09, the pilot of another aircraft, which was in the area, reported that the airplane had crashed into the water. WRECKAGE AND IMPACT INFORMATION According to U.S. Coast Guard channel charts, the airplane was found submerged in approximately 44 feet of water, 1,490 feet from the threshold of runway 9, the intended landing runway. The wreckage debris was located slightly to the south of the extended centerline for runway 9. The main wreckage was located in a generally compact area. According to photographs provided to the NTSB during the night recovery operation, the airplane came to rest inverted and was resting on the floor of the bay. Right Wing The right wing remained attached to the forward attachment point and all access panels remained in place. Crush damage was evident on the outboard 3 feet, 3 inches of the wing structure . The trailing edge wing root exhibited compression fractures from the attachment point of the fuselage, outward for about 4 feet, 1 inches. The outboard 21 inches of the right wing aileron was bent slightly in the negative direction, and the inboard section of the wing flap, about 24 inches in length, exhibited damage that was similar to crush damage. The wing strut was bent in the negative direction about 27 inches from the wing attach point. The right flap drive motor worm gear was measured at 2.5 inches, which correlated to a 10-degree flap position. The aileron and flap remained attached to their respective attachment points. The interconnect control cable to both ailerons exhibited broomstrawing and the control cable associated with the right aileron was separated in a manner consistent with tensile overload. The top left doorpost pulley exhibited signs of scoring on the pulley rim. A section of the right aileron control direct cable, which exhibited signatures consistent with corrosion at the failure point, and its associated pulley, were removed and sent to the NTSB Materials Laboratory for examination. The other cables did not exhibit signs of excessive corrosion at the failure points. All cables appeared to have had a lubricant applied and were oily in nature; however, a section of cable on the aileron control direct cable at the fracture point was devoid of lubrication. Empennage The empennage exhibited impact damage and fractures aft of the cargo compartment and remained attached to the cabin area by rudder and elevator cables. Continuity to the rudder from the rudder pedals was confirmed. Continuity from the elevator to the empennage fracture point and then forward to the base of the cockpit control column was confirmed. The trim tab was found at the 10-degrees trailing edge up setting. The emergency locator transmitter (ELT) remained secured and attached to the sidewall of the empennage. The ELT switch was found in the "ON" position; however, no reports of an ELT activation were reported. The ELT had a label affixed with the following notation, "Replace Battery June 2014." Examination of the ELT revealed saltwater intrusion and corrosion on the internal mechanism and batteries. Left wing The left wing remained attached at the attachment point, and all access panels remained in place. The outboard 8 feet, 10 inches, as measured from the wingtip, of the leading edge exhibited crush damage. The aileron and flap remained attached. The wing flap position could not be determined due to cable overload and the flap moved freely in the flap track. The inboard 28 inches of the wing leading edge, as measured from the wing root, exhibited crush damage. The aileron was slightly bent in an area 53 to 59 inches from the inboard edge. Cables associated with the aileron exhibited signs of tensile overload or broomstrawing. All cables associated with the flight controls appeared to be oily in nature and were lubricated. Engine The engine remained attached to the firewall by five electrical wires, the oil line, and a fuel line; all engine mount brackets were fractured from impact. The engine was separated from the airframe to facilitate examination. The magnetos remained attached to the engine. They were removed and rotated smoothly when manually turned. The left magneto impulse coupling was observed to be operating; however, spark was could not be produced. Salt water corrosion was observed on in the interior and exterior of the unit. The oil filter was removed and oil was present as well as salt water. The bottom spark plugs were removed and the engine was rotated using the propeller blade attached to the hub. Continuity was confirmed from the propeller hub through the rear accessory pad. Compression was noted on all cylinders and during rotation, salt water expelled through the No. 1 cylinder spark plug. Thumb compression was verified on all cylinders. Cylinder No.2 exhibited weaker suction and compression, as compared to the other three cylinders. The valve cover was removed, and both valves were observed operating as normal. The bottom spark plugs were removed. According to the Champion Spark Plug inspection chart, the spark plugs appeared light gray in color with normal wear. The propeller remained attached with no S-bending or tip curling noted; however, the propeller spinner exhibited slight torsional twisting and crush damage. The fuel strainer remained attached and was disassembled. The fuel screen exhibited signs of salt water intrusion and was partially covered with salt deposits. Examination of the nose wheel attachment point indicated the nose wheel was impact separated; however, the main landing gear remained attached. The nose wheel was not located. Doors The cargo door remained attached and in the locked position; however, due to the deformation of the empennage, located aft of the cargo compartment, the door was found opened. Both main cabin door handles were in the locked position and was verified by the door mechanism. However, both doors were ajar and it could not be accurately determined if they were closed or open prior to impact. Cockpit The pilot seat was found in the forward and secured position, typical for a "pilot flying" position. The co-pilot seat was in the aft and locked position. The pilot and co-pilot seats were found with the aft feet off their seat rails and the front feet were found attached to their seat rails. The aft seat base remained attached and the back hinge was separated from the base on the right side. The pilot's seat belt was cut by first responders, and the co-pilot's seat belt and shoulder harness remained latched across the co-pilot's seat. The co-pilot's control yoke was fractured almost flush with the instrument panel and was recovered in the pilot's hands. The co-pilot's control yoke exhibited a left bend, as viewed from sitting in the co-pilot's seat looking forward, at the point of the fracture. The pilot's control yoke remained attached. Operation of the pilot's control yoke revealed continuity from the yoke, through the interconnect cable and to the base of the control column. The magneto switch was located in the "BOTH" position and the key was absent. The throttle lever was about one-half extended and the mixture lever was in the full forward or "full rich" position. The carburetor heat was in the full forward or "CLOSED" position. The cockpit fuel selector valve was located in the "BOTH" position. The electric flap selector was located in the midpoint or "OFF" position. The flap gauge, located to the right of the throttle and mixture levers, indicated between 20 and 30 degrees flap setting, which correlated with the water line within the instrument. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was performed on the pilot on July 26, 2012, by the Instituto de Ciencias Forenses, División de Investigación Médico-Legal y Toxicológica, San Juan, Puerto Rico. The autopsy findings included "severe bodily trauma" and contributing was "inhalation of water." Forensic toxicology was performed on specimens from the pilot by the FAA Bioaeronautical Sciences Research Laboratory, Oklahoma City, Oklahoma. The toxicology report stated no ethanol, cyanide, carbon monoxide or drugs were detected in the blood. ADDITIONAL INFORMATION Materials Laboratory Two sections of the aileron cable and the left door post pulley were sent to the National Transportation Safety Board Materials Laboratory in Washington, D.C., for further examination. The report noted that visual inspection of the cable separation revealed severe corrosion of the cable wire over a length of about 2 inches, centered on the separation and less severe corrosion was noted about 1 inch on either side of the severe corrosion. Magnified optical examination of the separation area revealed that the majority of the cable wires were completely corroded through. The door post pulley visual inspection found moderate corrosion on the pulley bearing and spacer hardware. When manipulated by hand, the pulley bearing would not rotate. Four exemplar control cable segments were submitted for examination. The cables were 3/32 inch diameter zinc coated carbon steel and each segment had a swaged on ball at one end and a threaded fitting on the other end. Two of the cables measured 78 inches in total length and the other two cables measured 59 inches in total length. Microscopic examination revealed areas of corrosion on both longer cables; however, no broken wires or significant wear on any of the cables were noted. However, further cleaning revealed that the coating was missing in several areas and a few wires showed section loss. Visual examination of the other two cables revealed heavy corrosion deposits. Corrosion preventative compound was noted on the cable segments including but to a lesser extent in the corrosion areas. Cessna Aircraft Company Model 172 Series Service Manual Section 2A-30-01 "Corrosion" Section 6 "General" states in part, "This section contains maps which define the severity of potential corrosion on airplane structure. Corrosion severity zones are affected by atmospheric and other climatic factors…" The "North America Corrosion Severity Map" depicts the corrosion severity and lists Puerto Rico as "Severe." According to Section 2A-10-00, if an airplane operates more than 30% of the time in a zone shown as severe on the corrosion severity maps then the severe corrosion environment time limits apply. Section 2A-10-01 "Inspection Time Limits" indicates that every 600 hours or 12 months, whichever occurs first, that for the task labeled "ailerons" that a mechanic must: 1. Check aileron travel and cable tension. 2. Check aileron cable system, control cables and pulleys, in accordance with the flight cable inspection procedures in Section 2A-20-01, Expanded Maintenance, Control Cables. Section 2A-20-01 "Expanded Maintenance" Section 1.B (3) "Inspection of Control Cable" states in part the following: a) The control cable assemblies are subjected to a variety of environmental conditions and forms of deterioration that ultimately may be easy to recognize as wire/strand breakage or the not-so-readily visible types of corrosion and/or distortion. b) Broken Wire 1) Examine cables for broken wires by passing a cloth along the length of the cable. This will detect broken wires, if the cloth snags on the cable. Critical areas for wire breakage are those sections of the cable which pass through fairleads, across rub block and around pulleys. If no snags are found, then no further inspection is required. If snags are found or broken wires are suspected, then a more detailed inspection is necessary, which requires that the cable be bent in a loop to confirm the bro
Maintenance personnel’s improper lubrication of the right direct aileron control cable and failure to detect the severe corrosion of the cable during a maintenance inspection, which resulted in the in-flight failure of the cable, the pilot’s subsequent inability to maintain aircraft control, and the airplane’s impact with terrain.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
