N694ESRaytheon Aircraft HAWKER 800XP · 2004

On October 15, 2014, about 1522 mountain daylight time, a Raytheon Aircraft Company Hawker 800XP airplane, N694ES, experienced a hydraulic malfunction and landed gear up at the Denver International Airport (DEN), Denver, Colorado. The two pilots and one crew member were not injured and the airplane received minor damage. The airplane was registered to GLO LLC and operated by Eaton Metals under the provisions of 14 Code of Federal Regulations Part 91 as a business flight. Visual meteorological conditions prevailed for the flight, which operated on an instrument flight rules flight plan. The flight originated from Centennial Airport (APA), Englewood, Colorado, and was en route to Arnold Palmer Regional Airport (LBE), Latrobe, Pennsylvania.According to information provided by the operator, during the takeoff roll, the pilot felt and heard a vibration from the airframe. They continued the takeoff and retracted the landing gear. Personnel in the APA tower, radioed the pilot that they momentarily observed white smoke come from the airplane. A short time later, the airplane's hydraulic low pressure lights illuminated. The pilot returned to APA but was unable to lower the landing gear. The pilots attempted to extend the landing gear through the alternate gear extension procedures with no success. Due to the hydraulic system malfunction, the crew elected to divert to Denver International Airport (DEN) which had longer runways. The airplane was landed with the flaps and gear retracted on runway 34L (16,000 ft by 200 ft) at DEN. An examination of the takeoff runway at APA after the event did not find any evidence of foreign object debris (FOD).

A postaccident examination of the airplane revealed that the No. 2 (inboard) tire on the left main landing gear assembly had ruptured and the servo block appeared to have separated due to impact forces. The servo block is a hydraulic shuttle valve mounted on the landing gear extend/retract actuator that allows either normal or emergency hydraulic pressure to extend/retract the landing gear actuator. The servo block and mounting bolts were sent to the NTSB laboratory in Washington, D.C. An examination of the servo block and mounting bolts found that both mounting bolts exhibited signatures consistent with mechanical overstress. The fragments of the No. 2 tire were collected and sent to Goodyear for examination under supervision of the NTSB investigator-in-charge. A visual inspection of the fragments found wrinkles on the inner liner in the tire shoulder area consistent with over-deflection. There were localized areas of melted nylon on some of the tire's inner most layers. There were no visible signatures of cuts or FOD damage to the external layer of the tire. A microscopic examination of the tire fragments also did not reveal any cut or FOD damage that could have contributed to the tire failure. No manufacturing anomalies were detected with the tire.

A tire could be over-deflected if the tire was operated below the recommended pressure and/or if the tire was overloaded. According to the operator, tire pressures are checked prior to flight, but the pressures are not recorded, so it could not be determined if this tire was consistently under the recommended tire pressure. The operator was not aware of any overloaded condition the tire would have experienced previously.

Damage to the servo block would result in depletion of both normal and emergency hydraulic system pressures. A similar accident involving a Hawker 600A occurred on August 17, 1999, that was investigated by the NTSB (see NTSB report LAX99FA272). As a result of that accident, Raytheon Aircraft Company recommended Service Bulletin SB 32-2777 was released to address two reports of tire disintegration during takeoff in which pieces of tire struck the main landing gear retraction actuator, resulting in separation of the servo block from the actuator. The service bulletin recommended the replacement of the main landing gear jack with a landing gear jack that has improved servo block mounting hardware for improved resistance to tire debris. It was recommended that the actuators be replaced at the next actuator overhaul (5,000 cycles) or any other time the actuator was replaced. An actuator overhaul or replacement had not been required on the accident airplane due to its 2,199 cycles and thus the incident airplane did not have the improved servo block mounting hardware. A review of the Federal Aviation Administration's Service Difficulty Report database and Textron Aviation (formly Raytheon Aircraft Company) service department records did not contain any reports of failures involving the improved mounting hardware.

In addition, as a result of this accident the FAA issued Special Airworthiness Information Bulletin NM-15-24 alerting owners, operators, and maintenance technicians of the potential for damage to the servo block mounted to the main landing gear retraction actuator due to debris from tire tread separation during takeoff on affected airframes. The FAA recommended that owners, operators, and maintenance personnel of the affected airplanes follow the procedures outlined in Raytheon Aircraft Company Bulletin 32-3777, dated October 2006, at the earliest opportunity.