CHI07LA043

The airplane was on approach to the destination airport when the low hydraulic level and flow cockpit warnings annunciated in the cockpit. The flight crew was unable to extend the right main landing gear after conducting the normal and emergency landing gear extension procedures and by performing g-loading maneuvers. The airplane landed with the right wing main landing gear retracted causing substantial damage to the right wing and fuselage structures. The total loss of hydraulic power to the airplane flaps, spoilers, thrust reversers, and landing gear was caused by a ruptured hydraulic pressure hose assembly. The examinations of the accident and exemplar hoses revealed internal wear between the fiberglass within the hose's fire sleeve and the stainless steel braid. The accident hose and two of the three exemplar hoses did not show any markings or damage to the exterior of the sleeve to indicate the existence of the internal wear abrading the stainless steel braiding. Functional testing of the landing gear system revealed that the extension sequence varied during eight actuations, and, in one actuation, the left main landing gear remained retracted. Following the accident, the airplane manufacturer was in the process of amending the airplane maintenance manual rigging procedures for the landing gear system, and placing service time limits on hydraulic hoses.

History of flight

On December 17, 2006, at 1907 eastern standard time, a Cessna 560, N49NS, operated by Mid-Ohio Aviation Inc., received substantial damage on impact with terrain during a partial gear-up landing on runway at Akron-Canton Regional Airport (CAK), North Canton, Ohio. The flight crew reported that they were unable to extend the right main landing gear. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 135 passenger flight was operating on an instrument rules flight plan. The pilot, copilot, and three passengers were uninjured. The flight departed about 1745 from Teterboro Airport, Teterboro, New Jersey, and was en route to CAK.

The flight crew reported that the hydraulic level low and the hydraulic flow low annunciator panel lights illuminated while en route to CAK. They reportedly followed checklist procedures to extend the landing gear and upon pulling the auxiliary gear control handle only the nose and left main landing gears locked down. They did not see the right main landing gear extended when they looked through the airplane windows. They then attempted to extend the right main landing gear by yawing and turning the airplane and performing "several G-loading maneuvers." The flight crew performed two flybys at the CAK Air Traffic Control Tower in order to have air traffic controllers confirm that the right main landing gear was still retracted. The flight crew then actuated the pneumatic landing gear extension handle to ensure that the left main and nose landing gears were locked down. The airplane landed on runway 01 (7,601 feet by 150 feet, grooved asphalt) with the flaps retracted, right main landing gear retracted, spoilers, and thrust reversers inoperative.

Aircraft information

The Cessna 560, serial number 560-0116, airplane was inspected on April 19, 2006, when Phase B, 1-5, 11, 18, 22, and 49 inspections were performed at: aircraft total time 8,082.5 hours, total aircraft landings 7,789, total number one engine hours/cycles: 7,928.4/7,605 and total number two engine hours/cycles: 7,839.7/7,548. The airplane landing gear system was last tested during the phase 1-4 portion of the April 19, 2006, inspection. The airplane received its last inspection on September 12, 2006, at an aircraft total time of 8,236.5 hours.

The aircraft total time at the time of the accident was 8,356.9 hours. The airplane hour meter at the time of the accident was 5,546.2 hours.

Wreckage and impact information

Damage to the airplane included abrasion on the bottom right wing panels, main spar, and rear spar, which occurred during the landing rollout. Also, there was wrinkling to both sides of the fuselage near the rear bulkhead.

Examination of the airplane revealed a ruptured left hydraulic pressure hose assembly. The installation position of the hose was such that it did contact an adjacent structure/surface and was not restrained along its intermediate length. Examination of the landing gear system revealed that there were no separations within the mechanical control system. The right main landing gear uplock roller bearing was noted to possess scratches/marks.. The left main landing gear had a larger gap between the uplock and the uplock roller bearing than the right main landing gear uplock and roller bearing. The left main landing gear bearing did not possess similar features as did the right bearing. The hose assembly and both uplock bearings were sent to the National Transportation Safety Board (NTSB) Materials Laboratory for further examination.

Post accident operation of the landing gear was performed by repeated extension and retraction of the landing gear with the airplane on jacks and powered by a hydraulic cart and airplane battery power. The left and right main landing gears were lifted up into the retracted position. With the landing gear hydraulically stowed, the emergency landing gear handle was pulled "slowly." The nose landing gear was the first to extend at each actuation of the emergency landing gear handle. The right main landing gear extended before the left main landing gear during the first 3 or 4 actuations. Upon the sixth actuation, the left main landing gear extended before the right main landing gear extended. Upon the seventh extension, the right main landing gear extended and the left main landing gear remained retracted. Upon the eighth actuation, all of the landing gear extended with the left landing gear extending last. The T-handle overtravel beyond the main landing gear release point measured 0.32 inch (the maintenance manual specification is 0.50 inch).

Tests and research

Accident Hose Examination

The left hand hydraulic pressure hose assembly, identified by the Cessna 560 Parts Manual as part number AE2463531G0460, underwent examination at the NTSB Materials Laboratory. The hose had a metal identification tag stamped "TSO-C75 TYPE I-A P-F," "CM 3574D460B000S," "10 25/90." According to Stratoflex, the tag identification indicated a Stratoflex 124F003-6CR-0460 hose, which has a layered construction consisting of a polytetradfluorine inner tube, a single layer of corrosion-resistant steel (CRES) braid and a fire sleeve consisting of an internal glass fiber fabric and external silicon sleeve. The hose had been manufactured in 1990 and accumulated a total time in service of 8,356.9 hours and 8,077 cycles. There is no life limit in place relating to the hose.

The hose was 46 inches long with a straight fitting at one end and a 45-degree elbow fitting at the other end. The silicone outer layer of the fire sleeve for the hose ruptured between 13.5 - 15.5 inches from the straight fitting end of the hose. Adjacent to the clamp at the elbow fitting end of the fire sleeve, the silicone layer of the fire sleeve was cracked, and the crack appeared to be filled with an orange filler material. Once the fire sleeve was removed, wear was observed on the CRES braid primarily in three areas. These areas were located at 8.5 - 9.25 inches (area A), 9.75 - 16 inches (area B), and 16.5 - 18 inches (area C) from the straight fitting end. In each of these areas, wear was characterized by thinned wires; and in areas of greatest wear, wires were thinned to a chisel-like point with wire material missing between the chisel-like ends. The area of the CRES braid in the vicinity of the wear also appeared darker than the rest of the hose braid. Wear was also observed on the CRES braid opposite of the hose circumference at the three areas. There was less wear on the opposite side.

The exterior surface of the fire sleeve at each of the worn areas was intact. Some of the surface markings in area A were missing and the surface appeared disturbed. However, the fire sleeve outer surface in the area of wear had an overall appearance similar to that of the remainder of the fire sleeve. The thickness of the fire sleeve silicone layer was 0.044 inches. A close view of wear in Area A showed, in the area of greatest wear, wire thinned to a chisel point and missing material from between the chisel-like ends. Worn surfaces of the wires had linear scratch marks, and the width of the scratch marks was similar to the diameter of the glass fibers from the fire sleeve.

The polytetrafluorine inner tube was ruptured with a longitudinal crack near the middle of area B and the wire braid in the area was spayed outward. The wire ends in the ruptured area displayed a chisel-like appearance of the worn wire ends. Individual glass fibers were observed in the worn and ruptured area. The worn ends of the braid wires had linear markings, and the width of the linear markings appeared similar to that of the glass fiber diameter. Similar thinning and linear marks on the thinned surfaced were observed in area B.

The thickness of the fire sleeve silicone layer from the exemplar hoses was approximately 0.044 inches. Scanning electron microscopic (SEM) examination of the fire sleeve