Orlando, FL, USA
N568XL
LIBERTY AEROSPACE INCORPORATED LIBERTY XL
The commercial pilot reported that, while taxiing for takeoff, he felt "softness" in the brakes; however, they operated satisfactorily when he applied them to test their operation. The flight was cleared for takeoff, and the pilot thought that he had to expedite the takeoff due to traffic on final approach. After entering the runway at an angle and with a crosswind from the right, the right brake failed, causing the airplane to veer to the left. With runway lights and signs ahead, the pilot stopped braking, added power, and cleared the signs, then reduced power and collided with a berm. The airplane was equipped with a castering nosewheel, and ground steering was accomplished using differential braking. A discrepancy was noted with the o-ring of the right brake caliper during postaccident operational testing, which could correlate to the pilot's observation of "softness" in the brakes; however, the effect of the anomaly on brake operation could not be determined because the right brake was not functionally tested before the system was opened to the atmosphere. The pilot reported that factors contributing to the accident included the pressure he felt to expedite the takeoff given the airport traffic, his desire to return home quickly, and a perceived lack of maintenance facilities to troubleshoot the brake issue given that it was a weekend evening.
On February 20, 2016, about 1900 eastern standard time, a privately owned and operated Liberty Aerospace, Inc., XL-2, N568XL, experienced a runway excursion during takeoff and subsequent collapse of all landing gear at the Orlando International Airport (MCO), Orlando, Florida. The commercial pilot and one passenger were not injured, and the airplane which was being operated under the provisions of 14 Code of Federal Regulations (CFR) Part 91 as a personal flight, was substantially damaged. Visual meteorological conditions prevailed at the time and no flight plan was filed for the flight that was originating at the time of the occurrence, and was destined for Spruce Creek Airport, Daytona Beach, Florida.The commercial pilot/owner stated that he landed the tricycle gear airplane at MCO uneventfully, taxied to a fixed base operator, and secured the airplane; no discrepancies were reported with the airplane's toe brakes which are used for braking and steering. He met his wife who had flown from Germany at the commercial terminal, and both proceeded back to the airplane where he checked the oil quantity and fuel system for contaminants since 5.0 gallons of fuel were added. He started the engine and did a brake system check after rolling forward, reporting no discrepancies. He was given taxi clearance and taxied to the approach end of runway 18R, where he was informed to cross the runway and expect departure from runway 18L. He reported that all turns were made to the right. After crossing runway 18R he noted a "softness" in the brakes but stopped the airplane. He and his wife (non-pilot but familiar with the airplane) did a brake test by allowing the airplane to move forward slightly with low engine rpm and applied the brakes which stopped the airplane; no discrepancies were reported. With traffic on a four-mile final, the pilot was cleared to takeoff by air traffic control and perceived the need for an immediate departure. He added power and rolled onto the runway at an angle beginning a rolling takeoff. Upon entering the runway with a slight crosswind from the right, the right brake failed and the airplane veered to the left. Concerned that further asymmetric brake application could cause a roll over, or releasing of the brakes would result in a collision with runway signage, he stopped braking and added full power in an attempt to regain directional control and cleared the runway lights and signs. He then aborted the takeoff and landed in grass, where the airplane contacted a ridge or berm causing collapse of all landing gears. He also stated that flying at a commercial airport caused pressure to expedite his departure, and he was in a hurry to get his wife home. Compounding his decision to continue the flight were the lack of suitable maintenance on the airport on Saturday night. Prior to NTSB classification as an accident, the airplane was inspected by personnel from the Federal Aviation Administration (FAA), and no leakage was noted at either brake. The inspector also noticed deterioration and corrosion on the linings, and discoloration of the disk of the right brake, that was not present on the left. The airplane was then transported from MCO to another location where it was secured. An individual involved in recovery of the airplane from MCO disconnected the brake line from the right brake caliper, because the line was the only thing holding the landing gear to the airframe. The individual reported that the B-nut was tight, and after removing the brake line from the caliper, fluid came from the unattached line requiring him to place absorbent pads to catch the fluid leakage. No determination was made as to the fluid level in the brake reservoir, or the functionality of the right brake either by FAA or recovery personnel before the line was removed from the right brake caliper. Following recovery of the airplane to the secure location, inspection of the brake system by a FAA inspector revealed minimal fluid in the brake reservoir, and no fluid in the plastic tubing from it. The left brake caliper was attached to the landing gear and after loosening the brake line at the brake caliper, fluid was noted coming from the fitting. Both brake calipers were removed and retained. Inspection of the left brake caliper revealed it was free to move in the sliding pins, while the right brake caliper exhibited "excessive" sliding motion in the sliding pins when compared with the left brake caliper. Examination and operational testing of the left and right brake calipers was performed at the manufacturer's facility with FAA oversight. The manufacturer representative noted both brakes were received partially disassembled with backplates removed, tie bolts loose, and anchor bolt nuts removed. Neither brake exhibited evidence of overheating. The examination and testing of the left brake caliper revealed the linings were in good condition, with normal rotor surface conditioning noted, while the linings for the right brake exhibited corrosion or rust, a small crack in the lining from an outermost rivet hole to the edge of the lining, and evidence of edge crumbling around the perimeter of the lining. Both brakes were reassembled and installed on a bench for testing which revealed the left brake met the testing requirements, while the right brake exhibited leakage past the piston at 30 psi, which stopped after 1 minute resulting in 9.4 mL of leakage. Further testing to 600 psi (standard) did not result in any leakage and the pressure plates seated properly against the rotor. Following testing, both brake calipers were disassembled which revealed the o-ring for the left brake appeared intact and was generally in a round condition, while the o-ring for the right brake showed a recessed area, one linear indentation, a scuff on the outer edge, and was in a square shape. The o-ring of the right brake caliper was replaced and the caliper was subjected to additional testing which revealed no leakage. During the subsequent testing, the pressure plate was noted to be canted, but still allowed the plates to seat against the rotor. A dimension check of the components of the right brake revealed all dimensions met drawing requirements. The measured lining dimensions for both brakes were greater than the minimum specified by the airframe manufacturer. Review of the maintenance records revealed the airplane's last annual inspection was signed off as being completed on February 1, 2016, at aircraft total time of 1,141.0 hours. According to the logbook entry related to the inspection, the brakes were bled and serviced with MIL-5606 hydraulic fluid. The mechanic who performed the inspection indicated that, "…at no time did I disconnect brake lines. I did bleed the brakes using the bleed ports on the bottom of the calipers. It is unnecessary to disconnect the flexible lines to the brakes to remove the calipers for maintenance…." The airplane had accrued about 21 hours since the inspection was performed. The airplane owner reported the annual inspection occurred while the airplane was in his hangar and he was present the entire time. With respect to the brakes, they were inspected, bled of air, and tested by him at both seat positions with no discrepancies. Since the annual inspection was completed, excluding the accident flight, there have been no issues with the brakes. The owner did report 2 previous discrepancies in 2013 related to the right brake. Both events were attributed to be from incorrect installation of an o-ring on the piston at the right brake caliper. According to the Chapter 32 of the maintenance manual, the troubleshooting guide specifies that the failure of the brake calipers to hold could be caused by either: a) a liner worn below limits or damaged liner, b) liner(s) not conditioned, c) disc worn below limits, d) leaking hydraulic fitting, or e) air in brake system.
A failure of the right brake for reasons that could not be determined based on the available information. Contributing to the accident was the pilot's decision to continue the flight after experiencing a braking anomaly due to his perceived need for an expedited departure, his wish to avoid a flight delay, and his perceived lack of suitable maintenance facilities for timely troubleshooting of the brake system.
Source: NTSB Aviation Accident Database
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