NTSB Factual Report

HISTORY OF FLIGHT

On October 4, 2009, about 1240 eastern daylight time, a Cessna 210, N9443T, was substantially damaged during landing, after the landing gear failed to completely extend at Bowman Field Airport (LOU), Louisville, Kentucky. The certificated flight instructor and commercial pilot were not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the instructional flight conducted under 14 Code of Federal Regulations Part 91.

According to the flight instructor, the purpose of the flight was to conduct a flight review and instrument competency check for the commercial pilot. The takeoff was uneventful. During the flight which including holding, instrument approaches, and landings at nearby airports, the landing gear and flaps (both of which were hydraulically actuated) were cycled several times without incident.

Upon returning to LOU, and being cleared for landing on runway 24, the commercial pilot attempted to lower the landing gear but, after the gear-up light extinguished, the gear down light would not illuminate, and "no wheels" were observed when looking out of the airplane's side windows.

After advising the tower of the problem, they were "directed to orbit," south of the airport while they "worked on the problem." The circuit breaker for the landing gear "checked OK," and the flaps would not extend. The flight instructor also "pumped" the manual gear extension lever for "many minutes," without result.

They next flew past the tower for a visual inspection and at the same time, the flight instructor noticed that the airplane and landing gear was creating a shadow on the ground. The shadow indicated to him by its outline, that the nose landing gear was partially extended, its doors were partially open, and the main landing gear was "slightly" extended.

After multiple attempts to lower the landing gear, the flight instructor declared an emergency and asked for "fire trucks and EMS." He then took over control of the airplane while the commercial pilot stowed all of the unsecured items that were in the cockpit.

Once the emergency vehicles were in position, the flight instructor flew a "no flaps approach," and touched down at the "minimum safe speed." The commercial pilot then "pulled" the mixture control, shutoff the magnetos, used the starter to move the propeller so it would not be damaged by ground contact, turned off the master switch, and shutoff the fuel, to reduce the chance of fire.

As the airplane "scraped" down the runway, the airplane veered to the left, left the paved portion of the runway, tilted to the left, and came to rest with the left horizontal stabilizer and left wingtip contacting the ground.

PERSONNEL INFORMATION

According to FAA and pilot records, the flight instructor held a commercial pilot certificate with ratings for airplane single engine land, and instrument airplane. He reported 2878.7 total hours of flight experience. His most recent application for an FAA third-class medical certificate was dated July 23, 2008.

According to FAA records, the commercial pilot held ratings for airplane single engine land, and instrument airplane. His most recent application for an FAA third-class medical certificate was dated April 1, 2009.

AIRCRAFT INFORMATION

According to FAA and maintenance records, the airplane was manufactured in 1960. The airplane's most recent annual inspection was completed on December 12, 2008 and as part of that activity a new high pressure electrical fuel pump was installed in the nose wheel well. At that time the airplane had accrued 4,354.4 total hours of operation.

METEOROLOGICAL INFORMATION

The reported weather at LOU, at 1253, included: winds 220 degrees at 3 knots, visibility 10 miles, a few clouds at 3,800 feet, temperature 16 degrees C, dew point 6 degrees C, and an altimeter setting of 30.11 inches of mercury.

AIRPORT INFORMATION

According to the Airport Facility Directory, LOU had two runways oriented in a 6/24 and 15/33 configuration. Runway 24 was asphalt, in fair condition. The total length of the runway was 4,326 feet, and its width was 75 feet.

WRECKAGE AND IMPACT INFORMATION

Post accident examination by a Federal Aviation Administration (FAA) inspector revealed that the horizontal stabilizer had received substantial damage.

Examination of the nose landing gear wheel well reveled that a considerable amount of hydraulic fluid was present on the visible surfaces of the interior of the nose landing gear wheel well. The right side of the nose wheel tire was also wet with hydraulic fluid, as was the strut assembly.

Examination of the landing gear hydraulic lines in the nose gear wheel well area revealed that they were made of aluminum. Further examination also revealed that the nose gear door actuator line on the right side of the aircraft had separated at the ferrule and flare of the line. The "B" nut however, was still attached to the actuator, and the line was dripping hydraulic fluid. Examination of the rest of the hydraulic lines within the wheel well area exhibited no further indication of breakage or leaks.

Examination of the main landing gear wheel wells revealed no visual signs of leakage or line breakage.

TESTS AND RESEARCH

Examination of the failed hydraulic line by the Safety Board investigators revealed that no aluminum tubing identification was present on the failed hydraulic line. The failed hydraulic line was fractured at the flared end which attached to the nose landing gear actuator port. The straight lengths of the hydraulic line were not perfectly straight and generally included slight bends along the length. A portion of the fracture surface was in flat planes perpendicular to the outer surface of the tube with curving crack arrest lines and ratchet marks, which are features consistent with fatigue. Further examination revealed that the fatigue emanated from multiple origins on the lower surface of the tube. The fatigue region covered approximately one third of the fracture surface, and the features were relatively rough, which along with the multiple origins were consistent with low-cycle fatigue.

Beyond the fatigue boundary, the fracture features were rougher, and the fracture plane transitioned toward the aft direction. The changes in fracture plane were consistent with fracture under an upward bending load. Post-fracture rubbing and smearing was also observed across the surface. Crack arrest lines and transgranular features consistent with fatigue were observed in the fatigue region. The next approximately 1/3 of the fracture surface had a more dimpled appearance with some faint crack arrest lines, which was consistent with relatively high stress loading, possibly under cyclic loads. The remainder of the fracture surface was rough with dimple features consistent with overstress.

A portion of the hydraulic line was covered with a longitudinally-split black flexible tube wrapped with black electrical tape. An area of the covered portion of the hydraulic line showed a mark where the black wrapping tape and part of the underlying flexible tube was worn away consistent with contact with another object. The contact area was located on the aft side of the hydraulic line in the upper horizontal length near the bend at the right end of the horizontal length.

After removal of the black electrical tape and plastic sleeve, two other contact marks were discovered on the opposite side of the plastic sleeve. Examination of the underlying tubing also revealed the existence of two other wear marks, one of which exhibited a groove that was approximately 50 percent of the wall thickness deep.

ADDITIONAL INFORMATION

During review of photographs taken by the FAA it was discovered, that the mounting location of the high pressure electrical fuel pump that was installed as part of the maintenance activities associated with the annual inspection was located above and in close proximity to the failed hydraulic line. The contact marks which were discovered also were in close proximity to the fuel line fitting which were attached to the pump.

According to Advisory Circular, AC-43-13-1B CHG 1, (Acceptable Methods, Techniques, and Practices, Aircraft Inspection and Repair), hydraulic and pneumatic systems should be inspected for leakage, worn or damaged tubing, worn or damaged hoses, wear of moving parts, security of mounting for all units, safetying, and any other condition specified by the maintenance manual. A complete inspection includes considering the age, cure date, stiffness of the hose, and an operational check of all subsystems.

Tubing should not be nicked, cut, dented, collapsed, or twisted beyond approved limits. When inspection shows a line to be damaged or defective, the entire line should be replaced or, if the damaged section is localized, a repair section may be inserted. In replacing lines, tubing of the same size and material as the original line should be used.

Minor dents and scratches in tubing may be repaired. Scratches or nicks not deeper than 10 percent of the wall thickness in aluminum alloy tubing, that are not in the heel of a bend, may be repaired by burnishing with hand tools. Lines with severe die marks, seams, or splits in the tube should be replaced. Any crack or deformity in a flare is unacceptable and cause for rejection. A dent less than 20 percent of the tube diameter is not objectionable unless it is in the heel of a bend. A severely-damaged line should be replaced; however, it may be repaired by cutting out the damaged section and inserting a tube section of the same size and material.

NTSB Probable Cause

A malfunction of the landing gear extension system due to a fractured hydraulic line. Contributing to the accident was the inadequate inspection and maintenance of the hydraulic line.